Glossary Flashcards
1
Q
Edges refer to
A
Edges refer to: the connections or relationships between entities in a resource allocation graph.
2
Q
A back door (trapdoor)
A
A back door (trapdoor): is a mechanism that bypasses user authentication.
3
Q
A bad block (bad sector)
A
A bad block (bad sector): is a storage block that is no longer reliable for storing and retrieving data due to physical damage.
4
Q
A batch process
A
A batch process: performs a long-running and generally repetitive task that does not require any intervention from the user.
5
Q
A binary semaphore
A
A binary semaphore: can take only the values 0 or 1.
6
Q
A bitmap is a data structure where
A
A bitmap is a data structure where: each bit represents one disk block. A 1 indicates that the block is allocated and a 0 indicates that the block is free.
7
Q
A buffer is a
A
A buffer is a: register or an area of main memory used to hold data generated by a producer process or an input device and removed from the buffer at a later time by a consumer process or an output device.
8
Q
A buffer overflow attack
A
A buffer overflow attack: is an intrusion technique that exploits the fact that many programs do not check for array overflow, allowing an attacker to overwrite portions of memory beyond the legitimate scope of an input buffer.
9
Q
A capability list (CL)
A
A capability list (CL): associated with a domain D contents entries of the form (O, rights), where rights specify what operations a process in domain D may apply to object O.
10
Q
A child process
A
A child process: c of process p is a process created by p.
11
Q
A circular buffer
A
A circular buffer: is a fixed array of buffer slots filled by the producer and emptied by the consumer one slot at a time in ascending order, modulo the buffer size.
12
Q
A clustered block allocation scheme
A
A clustered block allocation scheme: links together sequences of contiguous blocks. The last block of any cluster points to the beginning of the logically next cluster.
13
Q
A computer’s physical memory (RAM) is
A
A computer’s physical memory (RAM) is: a hardware structure consisting of a linear sequence of words that hold a program during execution.
14
Q
A condition variable is
A
A condition variable is: a named queue on which processes can wait for some condition to become true.
15
Q
A critical section is
A
A critical section is: a segment of code that cannot be entered by a process while another process is executing a corresponding segment of the code.
16
Q
A device controller (device adapter) is
A
A device controller (device adapter) is: an electronic circuit capable of operating a specific I/O device using binary signals.
17
Q
A device driver is a
A
A device driver is a: device-specific program that implements I/O operations, requested by user applications or the OS, by interacting with the device controller.
18
Q
A digital signature is
A
A digital signature is: a bit string that uses public-key cryptography to undeniably link a document to the producer and guarantees that the document has not been altered in any way.
19
Q
A directed acyclic directory hierarchy
A
A directed acyclic directory hierarchy: organizes directories such that any directory at a given level may point to zero or more files or other directories at lower levels but also permits any file or directory to have more than one parent directory.
20
Q
A disk block cache
A
A disk block cache: is a set of main memory buffers that contain the most recently accessed disk blocks.
21
Q
A disk block is
A
A disk block is: a fixed sequence of bytes on the disk, which can only be accessed as a single unit using low-level read-block and write-block operations.
22
Q
A File allocation table (FAT) is
A
A File allocation table (FAT) is: an array where each entry corresponds to a disk block. The FAT keeps track of which disk blocks belong to a file by linking the blocks in a chain of indices.
23
Q
A File control block (FCB) is a
A
A File control block (FCB) is a: data structure associated with a filename that contains all relevant attributes of the file. FCBs are stored apart from file directories and are pointed to by the corresponding directory entries.
24
Q
A file directory (or folder) is
A
A file directory (or folder) is: a special-purpose file that records information about other files and possibly other directories.
25
A file extension is
A file extension is: a sequence of one or more characters following the file name.
26
A file header
A file header: is a portion of the file preceding the actual data and is visible to only the FS itself.
27
A file is
A file is: a named collection of information managed on secondary storage by the FS.
28
A file system (FS) is
A file system (FS) is: an integral part of every OS, whose function is to implement the concept of files.
29
A load module is
A load module is: a program or combination of programs in a form ready to be loaded into main memory and executed.
30
A lock
A lock: is a synchronization barrier through which only one process can pass at a time.
31
A logic bomb
A logic bomb: is unauthorized code inserted into the system and executed at a specified time to perform some destructive action.
32
A logical address is
A logical address is :an integer in the range [0 : m-1] that identifies a word in a logical address space.
33
A logical address space is
A logical address space is: an abstraction of physical memory, consisting of a sequence of imaginary memory locations in a range [0 : m-1], where m is the size of the logical address space.
34
A man-in-the-middle attack (MITM)
A man-in-the-middle attack (MITM): is an attack where the attacker secretly listens to, and possibly alters, the communication between two systems.
35
A message authentication code (MAC)
A message authentication code (MAC): is a short bit string attached to a message and used to confirm that the message came from the stated sender and has not been modified in transit.
36
A modified-bit (m-bit) is
A modified-bit (m-bit) is: a binary flag in each page table entry that indicates whether the corresponding page has been modified during execution.
37
A monitor is
A monitor is: a high-level synchronization primitive implemented using P and V operations.
38
A non-preemptive scheduling algorithm
A non-preemptive scheduling algorithm: allows a running process to continue until the process terminates or blocks on a resource.
39
A non-resident page refers to
A non-resident page refers to: a page that is not currently present in the main memory (RAM).
40
A one-time password
A one-time password: can be used only once and thus becomes useless when stolen.
41
A one-way hash
A one-way hash: function converts a variable-length input string into a fixed-length output string in a manner that cannot be inverted.
42
A page fault is
A page fault is: an interrupt that occurs when a program attempts to reference a non-resident page.
43
A page frame is
A page frame is: a fixed-size contiguous block of physical memory identified by a single number, the page frame number.
44
A page is
A page is: a fixed-size contiguous block of a logical address space identified by a single number, the page number.
45
A page table is
A page table is: an array that keeps track of which pages of a given logical address space reside in which page frames. Each page table entry corresponds to one page and contains the number or the starting address of the frame containing the page.
46
A parity bit
A parity bit: is a bit added to a string of bits to ensure that the total number of 1's in the string is even or odd.
47
A period
A period: is a time interval (typically in milliseconds or even microseconds) within which each input item must be processed.
48
A physical address is
A physical address is: an integer in the range [0 : n-1] that identifies a word in a physical memory of size n.
49
A physical CPU
A physical CPU: is a real hardware instance of a CPU.
50
A preemptive scheduling algorithm
A preemptive scheduling algorithm: may stop the currently running process and choose another process to run.
51
A present bit is
A present bit is: a binary flag in each page table entry that indicates whether the corresponding page is currently resident in memory.
52
A priority wait
A priority wait: has the form c.wait(p), where c is a conditional variable and p is an integer specifying a priority according to which processes blocked on c are reactivated.
53
A privileged instruction
A privileged instruction: performs critical operations that access I/O devices and the CPU's status and control registers.
54
A process creation hierarchy
A process creation hierarchy: is a graphical representation of the dynamically changing parent-child relationships among all processes.
55
#VALUE!
A process is deadlocked in a state s if the process is blocked in s and if no matter what state transitions occur in the future, the process remains blocked.
56
A process p is blocked on a resource r if
A process p is blocked on a resource r if: one or more request edges directed from p to r exist and r does not contain sufficient free units to satisfy all requests.
57
A process
A process: is an instance of a program being executed by an OS.
58
A protection domain
A protection domain: is a set of pairs , where rights specify what operations a process may perform on the object.
59
A RAID (Redundant Array of Independent Disks)
A RAID (Redundant Array of Independent Disks): is a set of disks viewed by the OS as a single mass storage device.
60
A read file operation
A read file operation: copies data from an open file to a specified area in main memory.
61
A real-time process is
A real-time process is: characterized by continual input, which must be processed fast enough to generate nearly instantaneous output.
62
A record is
A record is: a structure of related data items, possibly of different data types, identified within a file by a record number or a unique key field.
63
A reference count is
A reference count is: a non-negative integer associated with a file f, which indicates how many directories are pointing to the file.
64
A reference string is
A reference string is: the sequence of page numbers referenced by an executing program during a given time interval.
65
A referenced bit (r-bit) is
A referenced bit (r-bit) is: a bit associated with a page and is set automatically by the hardware whenever the page is referenced by any instruction.
66
A relative path name is
A relative path name is: a concatenation of file names starting with the current directory.
67
A relocation register contains
A relocation register contains: the physical starting address of a program or program component in memory.
68
A resource acquisition (acq r, m)
A resource acquisition (acq r, m): by a process p of m units of a resource r reverses the direction of the corresponding request edges to point from the units of r to p.
69
A resource allocation graph is completely reducible if
A resource allocation graph is completely reducible if: at the termination of the graph reduction algorithm all processes have been deleted.
70
A resource allocation graph
A resource allocation graph: shows the current allocation of resources to processes and the current requests by processes for new resources.
71
A resource claim graph is
A resource claim graph is: an extension of the general resource allocation graph. The extended graph shows the current allocation of resources to processes andall current as well as all potential future requests by processes for new resources..
72
A resource control block (RCB)
A resource control block (RCB): is a data structure that represents a resource.
73
A resource is allocated to a process if
A resource is allocated to a process if: the process has access to and is able to utilize the resource.
74
A resource is free if
A resource is free if: the resource may be allocated to a requesting process.
75
A resource release
A resource release: (rel r, m) operation by a process p of m units of a resource r deletes m allocation edges between p and r.
76
A resource request (req r, m)
A resource request (req r, m): by a process p for m units of a resource r creates m new edges directed from p to r.
77
A sandbox
A sandbox: is a small area of memory within which a program may execute and which guarantees that the program cannot access and jump to any location outside of the designated area.
78
A schedule is feasible if
A schedule is feasible if: the deadlines of all processes can be met.
79
A sector
A sector: is a portion of a track and is the smallest unit of data that can be read or written with a single r/w operation.
80
A seek operation
A seek operation: moves the current position of an open file to a new specified position.
81
A segment is
A segment is: a variable-size block of a logical address space identified by a single number, the segment number.
82
A segment table is
A segment table is: an array that keeps track of which segment resides in which area of physical memory. Each entry corresponds to one segment and contains the starting address of the segment.
83
A semaphore s is
A semaphore s is: a non-negative integer variable that can be accessed using only two special operations, P and V.
84
A source module is
A source module is: a program or a program component written in a symbolic language, like C, or an assembly language, that must be translated by a compiler or assembler into executable machine code.
85
A stable read
A stable read: guarantees to return a valid copy of any block.
86
A stable write
A stable write: guarantees that every block is updated atomically.
87
A state s is a safe state if
A state s is a safe state if: no sequence of state transitions exists that would lead from s to a deadlock state.
88
A state s is called a deadlock state if
A state s is called a deadlock state if: s contains two or more deadlocked processes.
89
A supervisor call (kernel call)
A supervisor call (kernel call): is a privileged instruction that automatically transfers execution control to a well-defined location within the OS kernel.
90
A symbolic link (or shortcut) is a
A symbolic link (or shortcut) is a: directory entry that points to a file or directory just like a regular entry but is treated differently with respect to deletion. A delete operation only removes the link but not the file itself.
91
A system call
A system call: is a request from an application for an OS service.
92
A thread control block (TCB)
A thread control block (TCB): is a data structure that holds a separate copy of the dynamically changing information necessary for a thread to execute independently.
93
A thread
A thread: is an instance of executing a portion of a program within a process.
94
A time quantum, Q
A time quantum, Q: is a small amount of time (typically 10 to 100 milliseconds) during which a process is allowed to use the CPU.
95
A track
A track: is one of many concentric rings on a magnetic disk surface.
96
A translation lookaside buffer (TLB) is
A translation lookaside buffer (TLB) is: a fast associative memory buffer that maintains recent translations of logical addresses to frames in physical memory for faster retrieval.
97
A trap (also called an internal interrupt)
A trap (also called an internal interrupt): is an interrupt triggered by the currently executing instruction.
98
A tree-structured directory hierarchy is
A tree-structured directory hierarchy is: a collection of directories organized such that (1) every directory points to zero or more files or directories at the next lower level, and (2) every file and directory except the root is pointed to by exactly one parent directory at the next higher level.
99
A Trojan horse
A Trojan horse: is a program that appears to provide a useful service but also contains a hidden function intended to violate computer security.
100
A virus
A virus: is a piece of executable code that embeds itself into legitimate programs and copies itself to other programs and systems with the intention of causing harm.
101
A wait-for graph is
A wait-for graph is: a resource allocation graph containing only processes where each process can have multiple incoming resource allocation edges but only one outgoing resource request edge.
102
A waiting list
A waiting list: is associated with every resource and contains all processes blocked on that resource because the resource is not available.
103
A word is
A word is: a fixed-size unit of data.
104
A worm
A worm: is an unauthorized program, which exploits one or more systems weaknesses to spawn copies of itself on other systems via computer networks.
105
A write file operation
A write file operation: copies data from an area in main memory to a specified open file.
106
Abstraction
Abstraction: is the act of removing unimportant details or attributes of objects in order to construct more general and less complex objects.
107
access right
access right: The ability to execute an operation on an object.
108
advanced configuration and power interface (ACPI)
advanced configuration and power interface (ACPI): Firmware common to PCs and servers that manages certain aspects of hardware, including power and device information.
109
advanced technology attachment (ATA)
advanced technology attachment (ATA): An older-generation I/O bus.
110
An absolute path name of a file
An absolute path name of a file: uniquely identified by an internal ID, f, is the concatenation of the directory and file names leading from the root to the file f.
111
An access list (AL)
An access list (AL): associated with an object O contains entries of the form (D, rights), where rights specify what operations a process in domain D may apply to object O.
112
An access matrix
An access matrix: is a representation of protection domains, where each row corresponds to one domain Di, each column corresponds to one object Oi, and the intersection of the row and the column records the rights that a process in domain Di has with respect to the object Oi).
113
An access method is
An access method is: a set of operations provided by the OS as part of the user interface to access files.
114
An aging register is
An aging register is: associated with a page and is shifted periodically to the right by 1 bit. Unless the most significant bit is set to 1, the page is aging in the sense that the associated register value is steadily decreasing.
115
An error correcting code (ECC)
An error correcting code (ECC): includes multiple parity bits in a string to permit the detection and automatic correction of some number of erroneous bits.
116
An interactive process
An interactive process: communicates with the user in the form of a dialog by receiving commands or data from the keyboard or a pointing device and responding by generating output on the user's terminal or another output device.
117
An interrupt handler
An interrupt handler: is a kernel function, invoked whenever an interrupt occurs, that determines the cause of the interrupt and invokes the appropriate kernel function to provide the response.
118
An interrupt
An interrupt: is an event that diverts the current execution of a program to a predefined location in the kernel in order to respond to an event.
119
An object module is
An object module is: the machine-language output of a compiler or assembler generated from a source module.
120
anonymous memory
anonymous memory: Memory not associated with a file. Pages not associated with a file, if dirty and paged out, must not lose their contents and are stored in swap space as anonymous memory.
121
Application program
Application program: A program designed for end-user execution, such as a word processor, spreadsheet, compiler, or Web browser.
122
asynchronous write
asynchronous write: A write that is buffered and written in arbitrary order, with the requesting thread continuing execution after the write is requested.
123
attack surface
attack surface: The sum of the methods available to attack a system (e.g., all of the network ports that are open, plus physical access).
124
attack
attack: An attempt to break a computer system's security.
125
attacker
attacker: Someone attempting to breach a computer system's security.
126
audit trail
audit trail: The collection of activities in a log for monitoring or review.
127
authentication
authentication: The process of correctly identifying a person or device. In cryptography, constraining the set of potential senders of a message.
128
back door
back door: A daemon left behind after a successful attack to allow continued access by the attacker. In cryptography, a method of gaining access to encrypted information without first having the secret keys. More generally, a method of passing arbitrary commands or information when an interface does not provide a standard method.
129
bad block
bad block: An unusable sector on an HDD.
130
basic file system
basic file system: A logical layer of the operating system responsible for issuing generic commands to the I/O control layer, such as "read block x," and also buffering and caching I/O.
131
Best-fit searches
Best-fit searches: the entire list and chooses the smallest hole large enough to accommodate the request.
132
Biometrics
Biometrics: are user authentication methods that measure, record, and analyze unique physical or behavioral characteristics of a person.
133
bit-level striping
bit-level striping: The splitting of data at the bit level, with each bit in a byte or word stored on a separate device.
134
block-device interface
block-device interface: The interface for I/O to block devices.
135
block-level striping
block-level striping: The splitting of data at the block level, with each block stored on a separate device.
136
block
block: A self-contained unit of work. The smallest physical storage device storage unit, typically 512B or 4KB. In the Grand Central Dispatch Apple OS scheduler, a language extension that allows designation of a section of code that can be submitted to dispatch queues.
137
blocking
blocking: In interprocess communication, a mode of communication in which the sending process is blocked until the message is received by the receiving process or by a mailbox and the receiver blocks until a message is available. In I/O, a request that does not return until the I/O completes.
138
boot block
boot block: A block of code stored in a specific location on disk with the instructions to boot the kernel stored on that disk. The UFS boot control block.
139
boot control block
boot control block: A storage block of data containing information needed by the system to boot from the volume containing the block.
140
boot disk
boot disk: A disk that has a boot partition and a kernel to load to boot the system. A device that has a boot partition and can store an operating system for booting the computer.
141
boot partition
boot partition: A storage device partition containing an executable operating system.
142
boot sector
boot sector: The first sector of a Windows boot device, containing the bootstrap code.
143
bootstrap loader
bootstrap loader: The small program that loads the kernel as part of the bootstrap procedure.
144
bootstrap
bootstrap: The set of steps taken at computer power-on to bring the system to full operation.
145
buffer cache
buffer cache: In file I/O, a cache of blocks used to decrease device I/O.
146
Buffer swapping is a
Buffer swapping is a: technique that allows the operations of a producer process and a consumer process to overlap by using two buffers.
147
buffer
buffer: A memory area that stores data being transferred (e.g., between two devices or between a device and a process).
148
Busy-waiting is
Busy-waiting is: the act of repeatedly executing a loop while waiting for some condition to change.
149
The C-Scan scheduling algorithm
The C-Scan scheduling algorithm: is a variant of the Scan algorithm that services requests in only one direction. When the outermost request is reached, the r/w head sweeps back to the opposite end of the disk and starts servicing requests again in the same direction.
150
C.signal
C.signal: reactivates the process at the head of the queue associated with the condition variable c.
151
C.wait causes the executing process to
C.wait causes the executing process to: block and be placed on a waiting queue associated with the condition variable c.
152
cache
cache: A temporary copy of data stored in a reserved memory area to improve performance. In the slab allocator, a cache consists of two or more slabs.
153
Ceph
Ceph: A brand of object storage management software.
154
Challenge-response
Challenge-response: is a method of user authentication that has the form of a dialogue between the user and the system.
155
character-stream interface
character-stream interface: The interface for I/O to character devices (like keyboards).
156
cloud storage
cloud storage: Storage accessed from a computer over a network to a distant, shared resource data center.
157
cluster
cluster: In Windows storage, a power-of-2 number of disk sectors collected for I/O optimization.
158
compartmentalization
compartmentalization: The process of protecting each system component through the use of specific permissions and access restrictions.
159
Computer security
Computer security: is the freedom from theft of or damage to hardware, software, or information, and from disruption or misdirection of services.
160
Concurrency
Concurrency: is the act of multiple processes (or threads) executing at the same time.
161
constant angular velocity (CAV)
constant angular velocity (CAV): A device-recording method in which the medium spins at a constant velocity and the bit density decreases from inner to outer tracks.
162
constant linear velocity (CLV)
constant linear velocity (CLV): A device-recording method that keeps a constant density of bits per track by varying the rotational speed of the medium.
163
content addressable storage
content addressable storage: Another term for object storage; so called because objects can be retrieved based on their contents.
164
context switch
context switch: A context switch is the transfer of control from one process to another.
165
controller
controller: A special processor that manages I/O devices.
166
copy semantics
copy semantics: The meaning assigned to data copying—e.g., whether a block write from a process allows the data to be modified after the write has been requested.
167
copy-on-write
copy-on-write: Generally, the practice by which any write causes the data to first be copied and then modified, rather than overwritten. In virtual memory, on a write attempt to a shared page, the page is first copied, and the write is made to that copy.
168
Cryptography
Cryptography: is a technique that allows a sender to transform plaintext into a ciphertext, which the receiver can transform back to the original plaintext.
169
cylinder
cylinder: On an HDD, the set of tracks under the read-write heads on all platters in the device.
170
data striping
data striping: The splitting of data across multiple devices.
171
Decryption
Decryption: is the act of transforming ciphertext into the original plaintext.
172
defense in depth
defense in depth: The theory that more layers of defense provide stronger defense than fewer layers.
173
Demand paging is
Demand paging is: the principle of loading a page into memory only when the page is needed, rather than at the start of the execution.
174
denial-of-service
denial-of-service: Preventing legitimate use of a system.
175
device controller
device controller: The I/O managing processor within a device.
176
device-status table
device-status table: A kernel data structure for tracking the status and queues of operations for devices.
177
direct I/O
direct I/O: Block I/O that bypasses operating-system block features such as buffering and locking.
178
Direct memory access (DMA) controller is
Direct memory access (DMA) controller is: a hardware component that allows devices to access main memory directly, without the involvement of the CPU.
179
discretionary access control (DAC)
discretionary access control (DAC): Optional, as opposed to mandatory, access control.
180
disk arm
disk arm: An HDD component that holds the read-write head and moves over cylinders of platters.
181
domain switching
domain switching: The mechanism for switching dynamic domains.
182
double buffering
double buffering: The copying of data twice (e.g., from a device to the kernel and then from the kernel to a process's address space), or the use of two buffers to decouple producers and consumers.
183
double caching
double caching: The problem in which the same data might be in two different caches; solved by a unified buffer cache.
184
driver end
driver end: The interface between STREAMS and the device being controlled.
185
dual-booted
dual-booted: A term describing a computer that can boot one of two or more installed operating systems.
186
Dynamic relocation
Dynamic relocation: postpones the binding of a logical address to a physical address until the addressed item is accessed during execution.
187
Edges refer to
Edges refer to: the connections or relationships between entities in a resource allocation graph.
188
Effective access time is
Effective access time is: the average time to access memory in the presence of page faults.
189
effective transfer rate
effective transfer rate: The actual, measured transfer rate of data between two devices (such as a computer and a disk drive).
190
Encryption
Encryption: is the act of transforming plaintext into ciphertext.
191
Encryption/decryption keys
Encryption/decryption keys: are parameters used by the encryption/decryption functions, respectively.
192
eSATA
eSATA: A type of I/O bus.
193
escape
escape: Generally, a method of passing arbitrary commands or information when an interface does not provide a standard method.
194
extended file system
extended file system: The most common class of Linux file systems, with ext3 and ext4 being the most commonly used file system types.
195
External memory fragmentation is
External memory fragmentation is: the loss of usable memory space due to holes between allocated blocks of variable sizes.
196
fibre channel (FC)
fibre channel (FC): A type of storage I/O bus used in data centers to connect computers to storage arrays. A storage-attachment network.
197
fibre channel (FC)
fibre channel (FC): A type of storage I/O bus used in data centers to connect computers to storage arrays. A storage-attachment network.
198
file descriptor (fd)
file descriptor (fd): UNIX open-file pointer, created and returned to a process when it opens a file.
199
file handle
file handle: Windows name for the open-file file descriptor.
200
file system
file system: The system used to control data storage and retrieval; provides efficient and convenient access to storage devices by allowing data to be stored, located, and retrieved easily.
201
file-control block (FCB)
file-control block (FCB): A per-file block that contains all the metadata about a file, such as its access permissions, access dates, and block locations.
202
file-organization module
file-organization module: A logical layer of the operating system responsible for files and for translation of logical blocks to physical blocks.
203
First-fit always starts the search from
First-fit always starts the search from: the beginning of the list and allocates the first hole large enough to accommodate the request.
204
flash translation layer (FTL)
flash translation layer (FTL): For nonvolatile memory, a table that tracks currently valid blocks.
205
flow control
flow control: Generally, a method to pause a sender of I/O. In networking, a technique to limit the rate of data flow (e.g., to avoid buffer overflow and packet loss on a router).
206
free-behind
free-behind: Sequential I/O performance optimization that removes a page or block from a buffer as soon as I/O to the next page is requested.
207
front-end processors
front-end processors: Small computers that perform certain tasks in an overall system; used by some systems to manage I/O and offload the general-purpose CPU.
208
FTL
FTL: The FTL is a component used in flash memory-based storage devices (such as SSDs) to handle the translation between logical block addresses (LBAs) used by the operating system and physical addresses on the flash memory chips.
209
Galois field math
Galois field math: An advanced error-correcting calculation done in some forms of RAID.
210
garbage collection
garbage collection: In general, recovery of space containing no-longer-valid data.
211
Guarantee mutual exclusion
Guarantee mutual exclusion: Only one process may be executing within the CS.
212
GUIA graphical user interface (GUI)
GUIA graphical user interface (GUI): presets various icons on the screen, which the user can click on in different ways to invoke services associated with the icons, or to reveal pull-down menus for additional tasks.
213
hacker
hacker: Someone attempting to breach computer security.
214
Hadoop file system
Hadoop file system: An example of object storage management software.
215
hard disk drive (HDD)
hard disk drive (HDD): A secondary storage device based on mechanical components, including spinning magnetic media platters and moving read-write heads.
216
hardware objects
hardware objects: The CPU, memory devices, input/output (I/O) devices, and any other physical components that are part of a computer
217
head crash
head crash: On an HDD, a mechanical problem involving the read-write head touching a platter.
218
high-performance event timer
high-performance event timer: A hardware timer provided by some CPUs.
219
horizontal scalability
horizontal scalability: The ability to scale capacity not by expanding one item but by adding more items.
220
host bus adapter (HBA)
host bus adapter (HBA): A device controller installed in a host bus port to allow connection of one or more devices to the host.
221
host controller
host controller: The I/O-managing processors within a computer (e.g., inside a host bus adapter).
222
host-attached storage
host-attached storage: Storage accessed through local I/O ports (directly attached to a computer, rather than across a network or SAN).
223
hot spare
hot spare: An unused storage device ready to be used to recover data (e.g., in a RAID set).
224
hypervisor
hypervisor: The computer function that manages the virtual machine; also called a virtual machine manager (VMM).
225
I/O bus
I/O bus: A physical connection of an I/O device to a computer system.
226
I/O channel
I/O channel: A dedicated, special-purpose CPU found in large systems like mainframes for performing I/O or offloading the general-purpose CPU.
227
I/O control
I/O control: A logical layer of the operating system responsible for controlling I/O, consisting of device drivers and interrupt handlers.
228
In a contiguous block allocation scheme
In a contiguous block allocation scheme: every file is mapped into a contiguous sequence of disk blocks.
229
InfiniBand (IB)
InfiniBand (IB): A high-speed network communications link.
230
Information leaking
Information leaking: is the disclosure of confidential or secret information by a legitimate user to an unauthorized user.
231
inode
inode: In many file systems, a per-file data structure holding most of the metadata of the file. The FCB in most UNIX file systems.
232
inode
inode: In many file systems, a per-file data structure holding most of the metadata of the file. The FCB in most UNIX file systems.
233
Internal fragmentation is
Internal fragmentation is: the loss of usable memory space due to the mismatch between the page size and the size of a program, which creates a hole at the end of the program's last page.
234
intruder
intruder: Someone attempting to breach security.
235
iSCSI
iSCSI: The protocol used to communicate with SCSI devices; used across a network for more distant access.
236
Kernel mode
Kernel mode: is the CPU state where both privileged and non-privileged instructions may be used.
237
labels
labels: In mandatory access control, identifiers assigned to objects and/or subjects. The label is checked by the operating system when an operation is requested to determine if it is allowed.
238
Linking is the act of
Linking is the act of: resolving external references among object modules and can be done statically, before loading, or dynamically, while the program is already executing.
239
Load control is
Load control is: the activity of determining how many processes should be running concurrently at any given time to maximize overall system performance.
240
logical blocks
logical blocks: Logical addresses used to access blocks on storage devices.
241
logical file system
logical file system: A logical layer of the operating system responsible for file and file-system metadata management; maintains the FCBs.
242
logical formatting
logical formatting: The creation of a file system in a volume to ready it for use.
243
Login spoofing
Login spoofing: is an approach where a legitimate user presents a fake login screen to an unsuspecting user, who unwittingly supplies a valid login name and password to the imposter program.
244
Long-term scheduling
Long-term scheduling: decides when a process should enter the ready state and start competing for the CPU.
245
low-level formatting
low-level formatting: The initialization of a storage medium in preparation for its use as a computer storage device.
246
magnetic tape
magnetic tape: A magnetic media storage device consisting of magnetic tape spooled on reels and passing over a read-write head. Used mostly for backups.
247
man-in-the-middle attack
man-in-the-middle attack: An attack in which the attacker sits in the middle of the data flow of a communication, masquerading as the sender to the receiver and vice versa.
248
mandatory access control (MAC)
mandatory access control (MAC): Access control settings enforced in the form of system policy.
249
masquerading
masquerading: A practice in which a participant in a communication pretends to be someone else (another host or another person).
250
master boot record (MBR)
master boot record (MBR): Windows boot code, stored in the first sector of a boot partition.
251
master file table
master file table: The NTFS volume control block.
252
mean time between failure (MTBF)
mean time between failure (MTBF): The statistical mean time that a device is expected to work correctly before failing.
253
mean time to data loss
mean time to data loss: The statistical mean of the time until data is lost.
254
mean time to repair
mean time to repair: The statistical mean of the time to repair a device (e.g., to get a replacement and install it).
255
Memory compaction is
Memory compaction is: the systematic shifting of modules in memory, generally in one direction, to consolidate multiple disjoint holes into one larger hole.
256
Metadata is
Metadata is: information about the format and organization of a file's data and is generally stored in a file header.
257
mirrored volume
mirrored volume: A volume in which two devices are mirrored.
258
mirroring
mirroring: In storage, a type of RAID protection in which two physical devices contain the same content. If one device fails, the content can be read from the other.
259
Moore's law
Moore's law: formulated by the scientist Gordon Moore, is the observation that the number of transistors in an integrated circuit doubles about every two years.
260
mount table
mount table: An in-memory data structure containing information about each mounted volume. It tracks file systems and how they are accessed.
261
mount table
mount table: An in-memory data structure containing information about each mounted volume. It tracks file systems and how they are accessed.
262
mounting
mounting: Making a file system available for use by logically attaching it to the root file system.
263
Multilevel (ML) scheduling
Multilevel (ML) scheduling: maintains a separate queue of processes at each priority level. Within each level, processes are scheduled using RR.
264
Multiprogramming
Multiprogramming: is a technique that keeps several programs active in memory and switches execution among the different programs to maximize the use of the CPU and other resources.
265
need-to-know principle
need-to-know principle: The principle that only those resources currently needed should be available to use at a given time.
266
network time protocol
network time protocol: A network protocol for synchronizing system clocks.
267
network-attached storage (NAS)
network-attached storage (NAS): Storage accessed from a computer over a network.
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new state
new state: A newly created process is placed into the new state before the process is allowed to compete for the CPU.
269
Next-fit starts each search at
Next-fit starts each search at: the point of the last allocation.
270
nonblocking
nonblocking: A type of I/O request that allows the initiating thread to continue while the I/O operation executes. In interprocess communication, a communication mode in which the sending process sends the message and resumes operation and the receiver process retrieves either a valid message or a null if no message is available. In I/O, a request that returns whatever data is currently available, even if it is less than requested.
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nonvolatile memory (NVM)
nonvolatile memory (NVM): Persistent storage based on circuits and electric charges.
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NVM express (NVMe)
NVM express (NVMe): A high-speed I/O bus for NVM storage.
273
over-provisioning
over-provisioning: In non-volatile memory, space set aside for data writes that is not counted in the device free space.
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page cache
page cache: In file I/O, a cache that uses virtual memory techniques to cache file data as pages rather than file-system-oriented blocks for efficiency.
275
Page fault rate is
Page fault rate is: the number of page faults, f, occurring during a number of memory references, t. The page fault rate can be expressed as P = f/t, where 0 ≤ P ≤ 1.
276
Page replacement is
Page replacement is: the act of overwriting a page in memory with a different page loaded from the disk when needed.
277
page slot
page slot: In Linux swap-space management, a part of the data structure tracking swap-space use.
278
partition boot sector
partition boot sector: The NTFS boot control block.
279
partition
partition: Logical segregation of storage space into multiple area; e.g., on HDDs, creating several groups of contiguous cylinders from the devices' full set of cylinders.
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Peak transfer rate
Peak transfer rate: is the rate at which the data is streamed to or from the disk once the read/write head is at the beginning of the sector to be transferred.
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per-process open-file table
per-process open-file table: A kernel in-memory per-process data structure containing pointers to the system-wide open-file table, as well as other information, for all files the process has open.
282
permissions
permissions: An entity's access rights to an object (e.g., a user's access rights to a file).
283
phishing
phishing: A class of social engineering attacks in which a legitimate-looking e-mail or website tricks a user into breaching confidentiality or enabling privilege escalation.
284
physical formatting
physical formatting: The initialization of a storage medium in preparation for its use as a computer storage device.
285
platter
platter: An HDD component that has a magnetic media layer for holding charges.
286
Polling
Polling: is a technique to determine whether a device is busy or idle by reading a flag set and reset by the device controller.
287
pool
pool: In virtual memory, a group of free pages kept available for rapid allocation (e.g., for copy-on-write). In ZFS, drives, partitions, or RAID sets that can contain one or more file systems.
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positioning time
positioning time: On an HDD, the time it takes the read-write head to position over the desired track.
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Prevent deadlock
Prevent deadlock: Multiple processes trying to enter the CS at the same time must not block each other indefinitely.
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Prevent lockout
Prevent lockout: A process not attempting to enter the CS must not prevent other processes from entering the CS.
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Prevent starvation
Prevent starvation: A process (or a group of processes) must not be able to repeatedly enter the CS while other processes are waiting to enter.
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principle of least privilege
principle of least privilege: A design principle stating that every program and every privileged user of the system should operate using the least amount of privilege necessary to complete the job.
293
privilege escalation
privilege escalation: The enabling of more privileges than an entity (process, system, person) should have.
294
Process control block (PCB)
Process control block (PCB): A data structure that holds information for a process, including the current instruction address, the execution stack, the set of resources used by the process, and the program being executed.
295
Program relocation is
Program relocation is: the act of moving a program component from one address space to another. The relocation may be between two logical address spaces or from a logical address space to a physical address space.
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programmable interval timer
programmable interval timer: A hardware timer provided by many CPUs.
297
Programmed I/O
Programmed I/O: is a style of I/O programming where the CPU, running the device driver, performs the copying of all data between the I/O device controller and main memory.
298
protection domain
protection domain: In protection, a set of resources that a process may access. In virtualization, a virtual machine manager creates a protection domain for each guest to inform the CPU of which physical memory pages belong to that guest.
299
Protection
Protection: is the set of mechanisms and policies that guarantee computer security, including the confidentiality, integrity, availability, and authenticity of all data and services.
300
Public-key cryptography (asymmetric cryptography)
Public-key cryptography (asymmetric cryptography): uses different keys for encryption and decryption. The encryption key is made public while the decryption key is kept private.
301
RAID levels
RAID levels: The various types of RAID protection.
302
RAM drives
RAM drives: Sections of a system's DRAM presented to the rest of the system as if they were secondary storage devices.
303
raw disk
raw disk: Direct access to a secondary storage device as an array of blocks with no file system.
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raw disk
raw disk: Direct access to a secondary storage device as an array of blocks with no file system.
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raw I/O
raw I/O: Direct access to a secondary storage device as an array of blocks with no file system.
306
raw partition
raw partition: A partition within a storage device not containing a file system.
307
read-ahead
read-ahead: Sequential I/O performance optimization that reads and caches several subsequent pages when a read of one page is requested.
308
read-modify-write cycle
read-modify-write cycle: The situation in which a write of data smaller than a block requires the entire block to be read, modified, and written back.
309
Ready list (RL)
Ready list (RL): A list containing all processes that are in the ready state and thus are able to run on the CPU.
310
redundant arrays of independent disks (RAID)
redundant arrays of independent disks (RAID): A disk organization technique in which two or more storage devices work together, usually with protection from device failure.
311
Registry
Registry: A file, set of files, or service used to store and retrieve configuration information. In Windows, the manager of hives of data.
312
replay attack
replay attack: The malicious or fraudulent repetition of a valid transmission.
313
replication
replication: In file systems, the duplication and synchronization of a set of data over a network to another system. In storage, the automatic duplication of writes between separate sites.
314
Request vs Acuisition
Request vs Acuisition: A request is made by a process or task to the resource manager or operating system, indicating the need for a particular resource. Once a resource request is made, the system attempts to fulfill the request by allocating the requested resource to the process.
315
role-based access control (RBAC)
role-based access control (RBAC): A method of access control in which roles rather than users have access rights; applies the principle of least privilege to the protection of operating systems.
316
role
role: In RBAC, a named set of privileges that can be available to a user.
317
root partition
root partition: The storage partition that contains the kernel and the root file system; the one mounted at boot.
318
rotational latency
rotational latency: On an HDD, the time it takes the read-write head, once over the desired cylinder, to access the desired track.
319
scatter-gather
scatter-gather: An I/O method in which multiple sources or destinations of I/O are specified in one command structure.
320
Secret-key cryptography (symmetric cryptography)
Secret-key cryptography (symmetric cryptography): uses the same secret key for both encryption and decryption.
321
Sector forwarding
Sector forwarding: is a technique where a bad disk block b[i] is mapped to one of the spare sectors. The mapping process involves updating the storage device's internal logical-to-physical sector mapping table or file system structures to redirect any read or write operations targeting the original problematic block (b[i]) to the newly assigned spare sector.
322
Sector slipping
Sector slipping: is a technique where all blocks following a bad block b[i] are shifted to the right. The last block is mapped to a spare sector and b[i] is mapped to the sector occupied previously by block b[i+1].
323
sector slipping
sector slipping: The renaming of sectors to avoid using a bad sector.
324
sector sparing
sector sparing: The replacement of an unusable HDD sector with another sector at some other location on the device.
325
sectors
sectors: On an HDD platter, a fixed-size section of a track.
326
secure monitor call (SMC)
secure monitor call (SMC): An ARM processor special instruction that can be used by the kernel to request services from the TrustZone.
327
secure
secure: The state of a system whose resources are used and accessed as intended under all circumstances.
328
seek time
seek time: On an HDD, the time it takes the read-write head to position over the desired cylinder.
329
sense key
sense key: In the SCSI protocol, information in the status register indicating an error.
330
serial-attached SCSI (SAS)
serial-attached SCSI (SAS): A common type of I/O bus.
331
Service
Service: A software entity running on one or more machines and providing a particular type of function to calling clients. In Android, an application component with no user interface; it runs in the background while executing long-running operations or performing work for remote processes.
332
session hijacking
session hijacking: The interception of a communication.
333
Sharing is the act of
Sharing is the act of: linking the same copy of a module to multiple other modules.
334
Short-term scheduling
Short-term scheduling: decides which of the ready processes should run next on the CPU.
335
snapshot
snapshot: In file systems, a read-only view of a file system at a particular point in time; later changes do not affect the snapshot view.
336
social engineering
social engineering: A practice in which an attacker tricks someone into performing some task for the attacker (such as sending the attacker confidential information).
337
socket
socket: An endpoint for communication. An interface for network I/O.
338
software objects
software objects: The software components that make up a computer or device (files, programs, semaphores, etc.).
339
Solaris ZFS
Solaris ZFS: An advanced file system, first included as part of Solaris.
340
solid-state disk
solid-state disk: A disk-drive-like storage device that uses flash-memory-based nonvolatile memory.
341
spool
spool: A buffer that holds output for a device (such as a printer) that cannot accept interleaved data streams.
342
SRT (Shortest Remaining Time) algorithm schedules processes according to
SRT (Shortest Remaining Time) algorithm schedules processes according to: the remaining CPU time needed to complete the work. The shorter the remaining CPU time, the higher the priority.
343
Stable storage
Stable storage: is an approach to data management that uses redundancy, along with a strict protocol for reading, writing, and error recovery, to guarantee that all data remains consistent in the presence of media and crash failures.
344
Starvation
Starvation: is the indefinite postponement of a process while other processes are allowed to proceed. Both SJF and SRT can lead to starvation.
345
Static relocation
Static relocation: binds all logical addresses to physical addresses prior to execution.
346
storage-area network (SAN)
storage-area network (SAN): A local-area storage network allowing multiple computers to connect to one or more storage devices.
347
stream head
stream head: The interface between STREAMS and user processes.
348
stream modules
stream modules: In STREAMS, modules of functionality loadable into a STREAM.
349
STREAMS
STREAMS: A UNIX I/O feature allowing the dynamic assembly of pipelines of driver code.
350
Striping
Striping: is a technique where a sequence of data blocks, b[i], is distributed over n disks, such that disk[i] contains block b[i] modulo n.
351
Subsystem
Subsystem: A subset of an operating system responsible for a specific function (e.g., memory management).
352
superblock
superblock: The UFS volume control block.
353
suspended state
suspended state: A process may be placed into the suspended state even though the CPU and all resources are available.
354
Sustained data rate
Sustained data rate: is the rate at which the disk can transfer data continuously.
355
swap map
swap map: In Linux swap-space management, a part of the data structure tracking swap-space use.
356
swap-space management
swap-space management: The low-level operating-system task of managing space on secondary storage for use in swapping and paging.
357
Swapping is
Swapping is: the temporary removal of a module from memory. The module is saved on a disk and later moved back to memory.
358
synchronous writes
synchronous writes: Writes that are stored in the order in which they were issued, are not buffered, and have requesting threads wait for the writes to complete before continuing.
359
system disk
system disk: A storage device that has a boot partition and can store an operating system and other information for booting the computer.
360
System service
System service: A collection of applications included with or added to an operating system to provide services beyond those provided by the kernel.
361
System utility
System utility: A collection of applications included with or added to an operating system to provide services beyond what are provided by the kernel.
362
system-wide open-file table
system-wide open-file table: A kernel in-memory data structure containing a copy of the FCB of each open file, as well as other information.
363
tA shell script
tA shell script: is a program that implements a new operation by combining multiple commands and control statement into one named unit interpreted by the shell.
364
terminal concentrator
terminal concentrator: A type of front-end processor for terminals.
365
terminated state
terminated state: A process is placed into the terminated state when execution can no longer continue but before the PCB is deleted.
366
The 50% rule states that
The 50% rule states that: if the probability of finding an exact match for a request approaches 0, one third of all memory partitions are holes and two thirds are occupied blocks. Formally, n = 0.5 m, where n is the number of holes and m is the number of occupied blocks.
367
The aging page replacement algorithm
The aging page replacement algorithm: does not maintain pages sorted in the exact LRU order, but groups together pages referenced during a period of d consecutive references. Each period is represented by 1 bit in a periodically shifting aging register.
368
The arbitration rule
The arbitration rule: decides which process should proceed if two or more processes have the same priority.
369
The average turnaround time (ATT)
The average turnaround time (ATT): for a set of n processes is the mean of the n individual turnaround times.
370
The close file operation
The close file operation: reverses the effects of the open operation by saving the current state of the file in the FCB and freeing the OFT entry.
371
The CPU state
The CPU state: consists of all intermediate values held in any CPU registers and hardware flags at the time of the interruption.
372
The CPU utilization (U) is
The CPU utilization (U) is: the sum of the individual fractions of CPU times used by each process.
373
The create file operation causes
The create file operation causes: the creation of new named file.
374
The create process function
The create process function: allocates a new PCB, fills the PCB entries with initial values, and links the PCB to other data structures in the system.
375
The data transfer time
The data transfer time: is the time to transfer the desired number of bits to or from the disk, and is directly proportional to the disk's rotational speed.
376
The destroy file operation
The destroy file operation: removes an existing file from the FS.
377
The destroy process function
The destroy process function: destroys a process by freeing the PCB data structure and removing any references to the PCB from the system.
378
The earliest deadline first (EDF) algorithm schedules processes according to
The earliest deadline first (EDF) algorithm schedules processes according to: the shortest remaining time until the deadline. The shorter the remaining time, the higher the priority.
379
The FIFO (First-In-First-Out) algorithm, also known as
The FIFO (First-In-First-Out) algorithm, also known as: FCFS (First-Come-First-Served), schedules processes strictly according to the process arrival time. The earlier the arrival, the higher the priority.
380
The FIFO page replacement algorithm
The FIFO page replacement algorithm: selects the page that has been resident in memory for the longest time.
381
The kernel
The kernel: of an OS is the minimal set of functions necessary to manage the system resources safely and efficiently.
382
The least-recently-used page replacement algorithm (LRU) selects
The least-recently-used page replacement algorithm (LRU) selects: the page that has not been referenced for the longest time.
383
The magic number is
The magic number is: a short sequence of characters at the start of the file header, which identifies the file type.
384
The maximum claim of a process is
The maximum claim of a process is: the set of all resources the process may ever request.
385
The open file operation
The open file operation: prepares a file for efficient access and manipulation by retrieving relevant file information from the FCB and storing the information in an entry of the OFT.
386
The open file table (OFT) is
The open file table (OFT) is: a data structure that keeps track of all files currently in use to facilitate efficient access to and manipulation of the files.
387
The optimal page replacement algorithm
The optimal page replacement algorithm: selects the page that will not be referenced for the longest time in the future.
388
The optimal working set of a process is
The optimal working set of a process is: the set of resident pages that will still be needed in the immediate future and thus should remain resident.
389
The OS shell
The OS shell: is a command interpreter that accepts and interprets textual commands issued by the user via a keyboard.
390
The page-fault-frequency replacement algorithm
The page-fault-frequency replacement algorithm: takes a direct approach to controlling the page fault rate by adjusting the current resident set based on how frequently consecutive page faults occur. By adjusting the resident set based on the frequency of consecutive page faults, the page-fault-frequency algorithm aims to retain frequently accessed pages in the main memory while evicting infrequently accessed pages.
391
The parent process
The parent process: of a process p is the process that created p.
392
The principle of locality states that
The principle of locality states that: locations accessed recently are more likely to be accessed again than locations accessed in the distant past.
393
The priority of a process (or thread)
The priority of a process (or thread): is a numerical value that indicates the importance of the process relative to other processes.
394
The rate monotonic (RM) algorithm schedules processes according to
The rate monotonic (RM) algorithm schedules processes according to: the period. The shorter the period, the higher the priority.
395
The release resource function
The release resource function: allocates the resource r to the next process on the r's waiting list. If the waiting list is empty, r is marked as free.
396
The request resource function
The request resource function: allocates a resource r to a process p or blocks p if r is currently allocated to another process.
397
The response time of a process is
The response time of a process is: the elapsed time from the submission of a request (pressing the Enter key or clicking a mouse button) until the response begins to arrive.
398
The root of a tree-structured directory hierarchy is
The root of a tree-structured directory hierarchy is: the highest level directory, which does not have a parent directory.
399
The rotational delay (rotational latency)
The rotational delay (rotational latency): is the time to wait for the desired data item to pass under the r/w head.
400
The round-robin (RR) algorithm uses
The round-robin (RR) algorithm uses: a single queue of processes. The priority is determined solely by a process's position within the queue. The process at the head of the queue has the highest priority and is allowed to run for Q time units. When Q ends, the process is moved to the tail of the queue and the next process now at the head of the queue is allowed to run for Q time units.
401
The Scan scheduling algorithm
The Scan scheduling algorithm: mimics the behavior of an elevator in a building. The r/w head maintains a current direction of travel and services all request sequentially in the current direction. When the outermost request is reached, the direction is reversed and the algorithm services all requests in the opposite direction.
402
The scheduler function
The scheduler function: determines which process should run next and starts the process.
403
The second-chance page replacement algorithm
The second-chance page replacement algorithm: is a coarse-grain approximation of LRU. The algorithm uses the r-bit to divide all pages into only two categories: recently referenced and not recently referenced. A page is selected from the not-recently referenced category.
404
The seek time
The seek time: is the time to move the r/w head from the current position to the track containing the desired data.
405
The Shortest seek time first (SSTF) scheduling algorithm
The Shortest seek time first (SSTF) scheduling algorithm: considers the list of all pending requests and always selects the request that requires the shortest travel distance from the current position.
406
The SJF (Shortest Job First) algorithm, also known as
The SJF (Shortest Job First) algorithm, also known as: SJN (Shortest Job Next), schedules processes according to the total CPU time requirements. The shorter the required CPU time, the higher the priority.
407
The test-and-set instruction (TS)
The test-and-set instruction (TS): copies a variable into a register and sets the variable to zero in one indivisible machine cycle.
408
The third-chance page replacement algorithm, also known as
The third-chance page replacement algorithm, also known as: the not-recently-used page replacement algorithm (NRU), is a coarse-grain approximation of LRU, which divides pages into 4 categories based on the 4 possible combination of the r- bit and the m-bit.
409
The TLB's hit ratio is
The TLB's hit ratio is: the fraction of memory accesses that find a match in the TLB.
410
The turnaround time
The turnaround time: of a process is the time between arrival and departure, and is the sum of the total CPU time and the waiting time.
411
The working set (WS) of a process at time t is
The working set (WS) of a process at time t is: the set of pages referenced during the past d memory operations preceding t.
412
The working set page replacement algorithm
The working set page replacement algorithm: uses a trailing window of size d superimposed on the RS to determine the size and composition of the working set at time t.
413
Thrashing is
Thrashing is: an execution state during which most of the time is spent on moving pages between the memory and the disk while the CPU is mostly idle and no process is making any real progress.
414
threat
threat: The potential for a security violation.
415
time sharing
time sharing: Multiple processes may run on one physical CPU using a technique known as time sharing.
416
Time-sharing / multitasking
Time-sharing / multitasking: is an extension of multiprogramming where the CPU is switched periodically among all active computations to guarantee acceptable response times to each user.
417
TLB
TLB: The TLB is a hardware cache used in processors to accelerate virtual address to physical address translation. It stores recently accessed mappings between virtual addresses and physical addresses.
418
track
track: On an HDD platter, the medium that is under the read-write head during a rotation of the platter.
419
transfer rate
transfer rate: The rate at which data flows.
420
TrustZone (TZ)
TrustZone (TZ): ARM processor implementation of the most secure protection ring.
421
Under the multilevel feedback (MLF) algorithm
Under the multilevel feedback (MLF) algorithm: a newly arriving process enters the highest-priority queue, N, and is allowed to run for Q time units. When Q is exceeded, the process is moved to the next lower priority queue, N-1, and is allowed to run for 2Q time units. The quantum size is doubled with each decreasing priority level.
422
unified buffer cache
unified buffer cache: In file I/O, a cache used for both memory-mapped I/O and direct file I/O.
423
unified virtual memory
unified virtual memory: In file I/O, the use of page caching for all types of I/O (explicit file system I/O and page fault I/O).
424
universal serial bus (USB)
universal serial bus (USB): A type of I/O bus.
425
UNIX file system (UFS)
UNIX file system (UFS): An early UNIX file systems; uses inodes for FCB.
426
unstructured data
unstructured data: Data that are not in a fixed format (like a database record) but rather are free-form (like a twitter.com tweet).
427
USB drive
USB drive: Nonvolatile memory in the form of a device that plugs into a USB port.
428
User authentication
User authentication: is the act of verifying the identity of a person who wishes to connect to a computer or a network.
429
User mode
User mode: is the CPU state where only non-privileged instructions may be used.
430
utility storage
utility storage: An inServ feature in which storage space can be increased as needed.
431
Vectored I/O
Vectored I/O: An I/O method in which multiple sources or destinations of I/O are specified in one command structure.
432
Virtual CPU
Virtual CPU: A CPU that the process assumes is available only to itself.
433
Virtual memory (VM) is
Virtual memory (VM) is: a collection of one or more logical address spaces, each of which may exceed the size of physical memory.
434
virtual memory fork
virtual memory fork: The vfork() system call, which forks a child process, suspends the parent, and lets the child share the parent's address space for both read and write operations (changes are visible to the parent).
435
Virtualization
Virtualization: is the act of creating the illusion of having one or more objects with more desirable characteristics than the real object.
436
volume control block
volume control block: A per-volume storage block containing data describing the volume.
437
volume
volume: A container of storage; frequently, a device containing a mountable file system (including a file containing an image of the contents of a device).
438
wear leveling
wear leveling: In nonvolatile memory, the effort to select all NAND cells over time as write targets to avoid premature media failure due to wearing out a subset of cells.
439
With a linked block allocation scheme
With a linked block allocation scheme: the blocks containing a file may be scattered throughout the disk.
440
With an indexed block allocation scheme
With an indexed block allocation scheme: file blocks may reside anywhere on the disk. An index table is provided for each file, which keeps track of the blocks belonging to the file.
441
Worst-fit
Worst-fit: takes the opposite approach from best-fit by always choosing the largest available hole for any request.
