Midterm 1

Question 1

What is an operating system?

Answer 1

Hard to define precisely, but basically allows other programs and people to make the hardware useful

Question 2

What does a modern OS do?

Answer 2

Provides abstractions
Provides standard interface
Mediates resource usage
Consume resources

Question 3

What three parts make up the operating systems?

Answer 3

Kernel – schedules programs the user wants to run

Userspace – allows a person to run programs

Question 4

What types of things should the kernel do?

Answer 4

Interrupt handlers
Scheduler – who is currently on the block
(This is the part of the OS always in memory)

Question 5

True or false. Tasks and processes are the same

Answer 5

True

However, multitasking and multiprocessing are different

Question 6

What is a shell?

Answer 6

A task that functions as an interface between the user and an operating system, or an interface between programs.

Question 7

If we have the option to use #define (preprocessor) or the compiler, which should we use?

Answer 7

Compiler

Compiler variable will always take less than or equal to the memory of the #define variable. Errors with the variable will also be very confusing if its done with the preprocessor.

Question 8

What does on OS pass to an new task’s main function?

Answer 8

Two variables, argc and argv

argc is the size of the argv array and it can never be zero

Question 9

What is required of the “host” for our OS to work properly?

Answer 9

Non-blocking access to an input (keyboard) character

An assembly instruction to change the computer’s stack pointer

Question 10

What is a systems program?

Answer 10

Program associated with the OS

Question 11

What is an applications program?

Answer 11

Program not associated with the OS

Question 12

What is middleware?

Answer 12

Not an OS, not an application, its in the middle
Additional frameworks for developers
Another level of abstraction between the application and the OS
Code that might protect me, do multiple actions on a single commands, etc

Question 13

What is firmware?

Answer 13

Hardware initialization software

Question 14

What is a bootstrap program?

Answer 14

Initial program executed on PU (physical unit)

Question 15

What is a daemon?

Answer 15

Kernel associated services

Question 16

What is a device driver?

Answer 16

Device controller software

Question 17

What is asymmetric multiprocessing? Symmetric multiprocessing?

Answer 17

Each processor is assigned as specific task in asymmetric multiprocessing
Symmetric multiprocessing is when any processor can do any task, or in other words, they use the same shared memory

Question 18

What is a processor?

Answer 18

Controls the operation of the computer and performs its data processing functions. When there is only one processor, it is often referred to as the central processing unit (CPU).

Question 19

What is main memory?

Answer 19

Stores data and programs. This memory is typically volatile; that is, when the computer is shut down, the contents of the memory are lost. In contrast, the contents of disk memory are retained even when the computer system is shut down. Main memory is also referred to as real memory or primary memory.

Question 20

What are I/O modules?

Answer 20

They move data between the computer and its external environment. The external environment consists of a variety of devices, including secondary memory devices (e.g., disks), communications equipment, and terminals.

Question 21

What is the system bus?

Answer 21

Provides for communication among processors, main memory, and I/O modules.

Question 22

What is a chip?

Answer 22

Also called a socket, it contains multiple processors (called cores), which each have multiple threads to work on.

Question 23

What is an instruction cycle?

Answer 23

The processing required for the fetching and execution of a single instruction

Question 24

What is the PC?

Answer 24

Program counter

Holds the address of the next instruction to be executed. Goes sequentially throughout the program, fetching an instruction, storing it in the IR, and executing. The bits stored in the IR tell the computer what to do.

Question 25

In general, what are the four categories processor instructions fall into?

Answer 25

Processor-memory: Data may be transferred from processor to memory or from memory to processor.

Processor-I/O: Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.

Data processing: The processor may perform some arithmetic or logic operation on data.

Control: An instruction may specify that the sequence of execution be altered. For example, the processor may fetch an instruction from location 149, which specifies that the next instruction will be from location 182. The processor sets the program counter to 182. Thus, on the next fetch stage, the instruction will be fetched from location 182 rather than 150.

An instruction can also do a combination of the above actions

Question 26

How does a processor handle multiple interrupts?

Answer 26

1) On execution of one interrupt, interrupts become disabled. Right before returning to normal execution of instructions, interrupts are enabled again to process the rest. Interrupts are processed in sequential order this way (doesn’t set priorities).
2) Gives interrupts priority. Interrupts are executed but higher interrupts can interrupt those and take over. Before returning to the user program, an interrupt with higher priority than the user program will stop it and execute before returning to the program.

Question 27

What is a signal?

Answer 27

Asynchronous event notification to a process or multiple processes that something needs to be done. A software interrupt. Anybody can signal – hardware or software.

Question 28

When is a signal acknowledged?

Answer 28

When the signal is unblocked

Question 29

How are signals delivered to a process?

Answer 29

Every process has a signal variable. If a signal bit is set, it does the appropriate operation. Checks the signal bit every time the program does a context switch, which should be often.

Question 30

What operations are illegal within a signal handler?

Answer 30

Blocking operations

Question 31

How are parameters passed to a signal?

Answer 31

You can pass them through environment variables

Question 32

What signals might a process not handle?

Answer 32

Harmless signals like SIGSTOP

Question 33

How many signals might a signal support?

Answer 33

Usually 64, 1 per bit in the signal variable

Question 34

What is the difference between an interrupt and a trap?

Answer 34

An interrupt is coded while a trap is caused by hardware. A trap happens when, for example, an exception needs to be thrown.

Traps also deal with the current line of code being executed, like when there is an error with it. An interrupt does not have to do with the next line of code to be executed, but simply jumps to do something else.

Question 35

What is the purpose of an interrupt?

Answer 35

It allows the computer to run more efficiently. For example, if relatively slow hardware needs to do a subtask before it can use the next piece of information, an interrupt can leave the task behind to do something else while the hardware finishes. It will then return to finish the task.

Question 36

What is the purpose of interrupts intentionally coded into a user program?

Answer 36

It gives a person more control over the computer. A user can make custom interrupt handlers to do specific things.

Question 37

Describe spatial and temporal locality. What are these ideas used for?

Answer 37

Spatial locality is the idea that if one point in memory is accessed, it is more likely that memory in close proximity around it will also be accessed soon.

Temporal locality is the idea that if something is accessed in memory now, it will likely be accessed again in the near future.

Question 38

How do caches take advantage of spatial and temporal locality?

Answer 38

For spatial locality, if a memory point is accessed, the cache will store a whole block of memory around the accessed point instead of just the one variable in anticipation that those other points will be used soon.

Temporal locality is the same, except this only applies to the accessed variable in anticipation of the same variable to be called again in the near future.

Question 39

What are the 3 tradeoff relationships when it comes to memory and access speed?

Answer 39

Faster access time, greater cost per bit

Greater memory capacity, lower cost per bit

Greater memory capacity, slower access time

Question 40

What memory structures make up inboard memory?

Answer 40

Registers – highest speed, smallest capacity
Cache – higher speed, smaller capacity
Main memory – slower speed, higher capacity

Question 41

What three section are there in the memory hierarchy?

Answer 41

Inboard memory
Outboard storage
Off-line storage

Question 42

What kinds of things comprise outboard storage?

Answer 42

CD’s

External hard drives

Question 43

What does SMP stand for? What is it?

Answer 43

Symmetric multiprocessor
It is a computer with these characteristics:
1) Has 2 or more processors with comparable capabilities
2) The processors share the same main memory and I/O facilities and are connected such that they can access things in similar time
3) They share access to I/O devices
4) All processors can perform the same functions (symmetric)
5) The system is control by an OS that provides interaction between the processors at data element levels (other systems can only interact at file level for example)

Question 44

What benefits does an SMP have over a uniprocessor?

Answer 44

Better performance
Availability – if one processor fails, the system still functions (with a drop in performance from the lost processor)
Incremental growth – can add another processor for better performance
Scaling – vendors can offer better computers for more money by increasing processors implemented

Question 45

What are the three main objectives of an operating system?

Answer 45

Convenience – make the computer more convenient to use
Efficiency – use the resources the most efficient way possible
Ability to evolve – can add more functionality if desired

Question 46

List some services an operating system provides

Answer 46

Program development, program execution, access to I/O devices (easy reads and writes without knowing complex details of the I/O device), controlled access to files and the system, error detection and response, accounting (like a task manager), ISA, ABI, API.

Question 47

Why will a major OS evolve over time?

Answer 47

New types of hardware or hardware upgrades
New services
Fixes

Question 48

Map the “new building construction” components to the computer components, namely the builder (general contractor), workers, materials, tools, and the new building.

Answer 48

Builder (general contractor) – operating system
Workers – Threads, cores/processors times threads per processor
Materials – Resources
Tools – Libraries
New building – task or process (or carrying them out I suppose)