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COMP30023 > Definitions > Flashcards

Definitions Flashcards

1
Q

Foreground processes

A

Those that interact with and perform work for users

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2
Q

Multiprogramming

A

The way the CPU rapidly switches between processes to give the illusion they are happening parallel to each other (pseudoparallelism)

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3
Q

Process

A

Instance of executing program

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4
Q

Program

A

Collection of instructions that perform a task when executed

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5
Q

Time-sharing

A

Multiprogramming with simultaneous terminal access to the machine by several users

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6
Q

Daemons

A

Processes that stay in the background to handle background activity (eg. Email)

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7
Q

Architecture

A

Set of rules and methods that describe functionality, organisation and implementation of computer systems

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8
Q

Embedded Systems

A

Dedicated systems within a larger mechanical or electrical system. These may not have a kernel mode.

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9
Q

Interpreted Systems

A

Systems that use interpretation, not hardware, to separate components (eg. Java-based operating systems)

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10
Q

System Call

A

Programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on

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11
Q

Abstraction

A

Concealing complex ideas and systems with a simpler one that the user or programmer interacts with

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12
Q

Multiplexing

A

Sharing of resources

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13
Q

Program Counter

A

Memory address of next instruction to be fetched

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14
Q

Stack Pointer

A

Points to top of current stack in memory

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15
Q

Register

A

A quickly accessible location available to a CPU

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16
Q

PSW

A

Program status word.
Contains condition code bits which are set by comparison instructions.
Plays important role in I/O.
User progs can generally read entire thing but can only write parts.
A bit in the PSW controls whether CPU is in user or kernel mode.

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17
Q

Pipeline CPU

A

Executing one instruction, while decoding the next instruction, while fetching the next instruction

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18
Q

Superscalar CPU

A

Multiple execution units are present. Multiple instructions are fetched and decoded at once, then stored in a holding buffer until the relevant execution unit is free.

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19
Q

Redirection

A

When output from terminally is redirected from terminal to a file (func > file)

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20
Q

Batch Job

A

Totally automated

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21
Q

Multicore Processor

A

Has multiple CPUs

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22
Q

Process Group

A

A process and all of its descendants in UNIX form a process group

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23
Q

Handle (token)

A

A token given to a parent process in Windows, allowing it to control a child. Can be given to other processes to allow them to control each other.

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24
Q

Multithreading

A

A single process having multiple threads

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25
Q

Lightweight Process

A

This another name for thread

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26
Q

Thread

A

(aka thread of execution or lightweight process) Sequential execution stream within process
These are used by CPU.

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27
Q

Cache

A

Collection of heavily accessed pages in main memory for easy access

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28
Q

FSM

A

Finite state machine. Machine exists in a finite state that can altered by external events. Allows efficiency with a single thread.

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29
Q

Nonblocking System Call

A

Returns almost immediately. Lengthy calls will give output later in the form of an event, message or signal

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30
Q

Thread Table

A

Each thread has its own thread table, containing properties unique to the thread. When a thread is moved to ready or to blocked, the information required to restart the thread is stored here

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31
Q

Process Table

A

Data structure maintained by the OS to facilitate context switching and scheduling,

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32
Q

Context Switching

A

Switching of CPU from one thread or process to another

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33
Q

Process Control Block

A

One entry within a process table. Contains information required to restart program if moved to blocked or ready states. This includes program counter, stack pointer, memory allocation and status of open files, accounting and scheduling info

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34
Q

Interrupt Vector

A

Address of interrupt handler
Area of memory with replacements for SP, PSW and PC. Essentially table of functions or function pointers to deal with interrupts. There’s a function corresponding to each task we want to deal with

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35
Q

IVT

A

Interrupt vector table. Associates interrupt handlers (ISR/interrupt service routine) with interrupt requests in a table of interrupt vectors

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36
Q

Interrupt

A

Alerts processor of higher priority process that requires immediate CPU attention
These have different priorities

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37
Q

Upcall

A

A call from a lower-level subsystem (kernel) to a higher-level subsystem (user)

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38
Q

Jacket

A

(aka wrapper) Code placed around a system call to determine if it will read or block, before the call is made (prevent blocking in user-level threads)

39
Q

Page Fault

A

If program calls or jumps to an instruction that is not in main memory, a page fault occurs. OS will go get instruction from disk

40
Q

Popup Thread

A

When a message arrives, the system creates a new thread to handle it. This thread is a popup thread.

41
Q

IPC

A

Interprocess Communication. The communication between processes.

42
Q

Reentrant

A

Reentrant procedures can be entered again before a return from the first call to the procedure has been returned from

43
Q

Race Conditions

A

Situations with two or more processes reading or writing to the same shared data where final result depends on who runs at what time

44
Q

Mutual Exclusion

A

Ensuring that if one process is using a shared data file, no other process can access it at that time

45
Q

Critical Region

A

(aka critical section) Part of program where shared memory is accessed (shared being by multiple processes)

46
Q

Busy Waiting

A

Continually testing a variable until some value appears
(eg. this isn’t needed in definition - this is for understanding
while (True):
while (var != value):
loop
)

47
Q

Spin Lock

A

A lock that uses busy waiting

48
Q

Priority Inversion Problem

A

In the case of achieving mutual exclusion, priority inversion problem is when a low priority process is in the critical region and a high priority process wants to enter. The preference should be given to the high priority task, but it must wait for low priority to finish.

49
Q

Atomic Action

A

An action all completed at once. It cannot be interrupted. Either it all happens or it doesn’t happen at all.
In synchronisation, a test-and-set atomic instruction prevents accesses to the word/value between the read and write

50
Q

Binary Semaphore

A

A semaphore initialised to 1 and used by 2 or more processes to ensure only one can enter critical region at given time

51
Q

Mutex

A

Variable that can be in one of two states: locked or unlocked

52
Q

Deadlock

A

Two processes that both end up and remain blocked forever

53
Q

Monitor

A

Collection of procedures, variables and data structures that are grouped together. Only one process can be active in a monitor at any instant.

54
Q

Condition Variable

A

Used for blocking in monitors. These variables wait for a condition to become true

55
Q

Message Passing

A

Method of IPC that uses 2 primitives, send and receive (system calls)

56
Q

Starvation

A

When processes continually do work but make no progress

57
Q

Compute-Bound Processes

A

Those that spend most of their time computing (rather than waiting)

58
Q

I/O-Bound Processes

A

Those that spend most of their time waiting for I/O (rather than computing)

59
Q

Non Preemptive Scheduling Algorithm

A

Picks up process to run and lets it run until it blocks or voluntarily releases CPU

60
Q

Preemptive Scheduling Algorithm

A

Allows process to run for a set amount of time. That is, clock interrupt occurs at end of given time interval and CPU control is given back to scheduler

61
Q

Throughput

A

Number of jobs per hour that system completes

62
Q

Turnaround Time

A

Statistically average time from the

moment that a batch job is submitted until the moment it is completed. How long user has to wait for output.

63
Q

Degree of Multiprogramming

A

This occurs in a 3-level scheduling algorithm. It is how many processes are to be stored in memory.

64
Q

Quantum

A

Designated time interval

65
Q

Aging

A

Estimating the next value in a series by taking the weighted average of the current measured value and the previous estimate (a=1/2 is good)

66
Q

Main memory

A

RAM

67
Q

Memory manager

A

Part of OS that manages (part of) memory hierarchy

68
Q

ROM

A

Read only memory

69
Q

BIOS

A

Basic input output system

70
Q

Memory Compaction

A

When swapping creates holes in memory, processes can be moved up or down to create consecutive holes that join together to form one big hole.

71
Q

Overlay

A

Little pieces that a program has been split into

72
Q

Virtual address space

A

Combination of virtual addresses

73
Q

MMU

A

(memory management unit) Maps virtual memory pages onto physical memory page frames

74
Q

Page frames

A

The units in physical memory that correspond to pages in virtual memory

75
Q

Page table

A

Data structure used by virtual memory to store mapping between virtual and physical addresses

76
Q

Volatile

A

Storage that only maintains its data while computer is powered

77
Q

TLB

A

(translation lookaside buffers aka associative memory) Small hardware device for mapping virtual addresses to physical addresses

78
Q

Principle of locality

A

Page replacement algorithms rely on the future following trends of the past. There are two types of locality: spatial and temporal

79
Q

Spatial locality

A

If a location was recently referenced, locations NEAR it are likely to be referenced soon

80
Q

Temporal locality

A

If a location was recently referenced, it is likely to be referenced again soon

81
Q

inode

A

(information node) contains all information kernel has about a file except its name

82
Q

ACL

A

(access control list or access matrix)

83
Q

Access matrix

A

(aka ACL or access control list)

84
Q

Link

A

Each reference to the same inode (file) from more than one directory entry is called a link

85
Q

Symbolic link

A

(symlink) Special kind of file that contains filename

86
Q

File descriptor

A

Small integer

87
Q

Network

A

Interconnected or intersecting configuration or system of components

88
Q

Internet

A

network of networks

89
Q

Packet

A

chunk of data

90
Q

Confidentiality

A

only sender and intended receiver should understand contents of message

91
Q

Authentication

A

sender and receiver want to confirm identity of each other

92
Q

Message integrity

A

the sender and receiver want to ensure that message is not altered without detection

93
Q

Access and availability

A

services must be accessible and available to users

94
Q

IPL

A

Interrupt priority level - how important interrupt is

COMP30023 (17 decks)

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