1.2

Question 1

What is an instruction set

Answer 1

A group of commands for a CPU in machine language.

Question 2

What does CISC stand for

Answer 2

Complex instruction set

Question 3

What is CISC

Answer 3

Use a full instruction set on the CPU, any instruction they need to be converted to machine code will be there.
Fewer registers

Question 4

What does RISC stand for

Answer 4

Reduced instruction set

Question 5

What is RISC

Answer 5

Small instruction set with only the most frequently used instructions are available

Question 6

Adv of RISC

Answer 6

Less heat
Lower cost
Physically smaller
Lower power consumption
Pipelining works better as independent instructions can be carried out at the same time
Each instruction only needs one clock cycle
Simpler hardware

Question 7

Disadv of RISC

Answer 7

More instructions to be carried out for one process
Runs at a lower clock speed
More programming code is needed
Compiler needs to do more work to translate from high level code to machine language

Question 8

What uses CISC

Answer 8

Desktop computers
Laptop computers

Question 9

What uses RISC

Answer 9

Smartphone
Tablets

Question 10

Adv of CISC

Answer 10

More intensive tasks will do better with CISC
Less programming code
Compiler has to do little work to translate from high level code to machine language

Question 11

Issues with CISC

Answer 11

Only 20% of instructions will be used, they all still need to be stored
Transistors use power and generate heat in turn, this needs additional cooling, this also takes up more space
A complex instruction takes more clock cycles to complete, this takes more time to process
Complex hardware making it more expensive than RISC
Cant support pipelining

Question 12

What are the 4 segments the OS divides the RAM into

Answer 12

Stack segment, free memory, data segment, code segment

Question 13

What does the stack segment store

Answer 13

Functions stored, changes size frequently, the stack segment can grow into free memory

Question 14

What does the data segment store

Answer 14

Stores all variables used

Question 15

What does the code segment store

Answer 15

Application code

Question 16

What is an OS

Answer 16

A program which manages all of the software and hardware on the computer

Question 17

Memory management

Answer 17

When the OS controls and coordinates a computers main memory

Question 18

What is paging

Answer 18

A fixed, physical sized division of main memory, pages are numbered, if a page hasn’t been used for a while it is moved to virtual memory, if a segment spans multiple pages, all pages are moved to virtual memory

Question 19

What is scheduling

Answer 19

The task of allocating CPU processor time amongst all running programs.

Question 20

What is the purpose of scheduling

Answer 20

Processes as many tasks as possible in a given time
Makes maximum use of CPU time
It will try to minimise the delay between when the user requests something to be done and when that task is completed.
Makes maximum use of resources such as input-output devices
Is able to prioritise jobs
It will ensure that no task is left uncompleted for too long, even if they are low priority
Is able to alter priorities according to need

Question 21

What are the types of scheduling algorithms

Answer 21

Round robin
First come first served
Shortest time remaining
Multi-level feedback queues

Question 22

What is round robin

Answer 22

Each program in a queue is given a set amount of processing time, the first processes is loaded into main memory, if the process is completed in the allocated time then the next processes is loaded immediately, however, if the process is not finished before the time runs out, it is put at the back of the queue.

Question 23

What are the advantages of round robin

Answer 23

It is simple to implement. Round Robin is a good algorithm if all the processes are more or less of similar priority and size.

Question 24

What are the disadvantages of round robin

Answer 24

It does not take priority into account
It does not consider some processes are short and some are long

Question 25

What is first come first served

Answer 25

The first process loaded into main memory is allowed to run to completion before the next process begins, processes are loaded into memory whenever space is available

Question 26

What are the advantages of first come first served

Answer 26

Simple algorithm to implement

Question 27

What are the disadvantages of first come first served

Answer 27

Once a job starts it prevents other jobs from being processed until it is completed
A job that needs to access a slow resource e.g. a printer, wastes processor time whilst it is waiting for that resource
It does not take into account the priority of a process.
It does not consider that some processes are short and others long.

Question 28

What is shortest job first

Answer 28

The shortest job in main memory is processed first, if the new process is shorter than the currently running process then the currently running process will be interrupted and the shorter one runs immediately

Question 29

What are the advantages of shortest job first

Answer 29

It ensures the maximum number of jobs are completed
It ensures that short jobs aren’t kept waiting while long processes tie up CPU resources.
It minimises the average time a process takes to complete.

Question 30

What are the dis advantages of shortest job first

Answer 30

Does not take into account the priority of a process.
If a long job is nearly completed, it will still be interrupted and put back in the queue when a shorter job arrives.
The scheduler can only estimate how long a job will take to complete, but its estimation could be wrong.
Particularly long jobs may never complete if shorter jobs continually keep ‘jumping the queue’.

Question 31

What are multi-level feedback queues

Answer 31

Every job is given a priority by the scheduler when it arrives and is sorted into the relevant queue. The queues themselves are sorted by one of the previously discussed algorithms. The high priority queue is completed first, and then each of the lower level queues in turn.
The scheduler is able to re-prioritise jobs at any time, moving them into the queue appropriate for their new priority. It may do this based on new information, or simply because a low priority job has been waiting for too long already.

Question 32

What are the advantages of multi-level feedback queues

Answer 32

Makes sophisticated use of process priority.
It ensures that higher priority processes run on time.

Question 33

What are the disadvantages of multi-level feedback queues

Answer 33

Complex to implement.
Not very efficient if all jobs have similar priority.
Low priority jobs may take an extremely long time to complete if the queue algorithm doesn’t compensate for wait-time, especially if new high-priority jobs keep arriving.