Computer architecture

Question 1

What cycle summarises the CPU processes?

Answer 1

The Fetch Decode Execute Cycle

Question 2

What does CPU stand for?

Answer 2

Central Processing Unit

Question 3

CPU
What do we call the step where the CPU fetches some data and instructions from main memory (RAM) and then store them in its own temporary memory called ‘registers’.

Answer 3

The Fetch Step

Question 4

In the CPU Fetch Stage, how does data get from the CPU to the RAM / Memory and back again?

Answer 4

Address Bus for CPU to RAM Memory

Data Bus for RAM / Memory to CPU

Question 5

CPU
What do we call the step where the CPU understands / works out what the instruction it has just fetched actually means.
The CPU ‘decodes’ the instruction and gets things ready for the next step.

Answer 5

The Decode Stage

Question 6

CPU
What do we call the step where data processing happens.
Instructions are carried out on the data.
Once a cycle has completed, another begins.

Answer 6

The execute stage

Question 7

The CPU basic actions are Fetch, Decode and Execute.

What are the areas the CPU is responsible for? (3 areas)

Answer 7

1) Control Unit
2) Immediate Access Store (IAS) or “Cache”
3) Arithmetic and Logic Unit (ALU)

Question 8

In the CPU the Control Unit has three main jobs.

What are they?

Answer 8

Control Unit:

1) It manages and monitors hardware on the computer to ensure the correct data goes to the correct hardware.
2) It manages the input and output signals ensuring these are dealt with correctly.
3) It manages the Fetch-Decode-Execute cycle.

Question 9

In the CPU what does the Immediate Access Store or Cache do?

Answer 9

This part stores the data which is to be immediately processed.
The CPU takes a chunk of data / instructions from the RAM and keeps it close so that it always has a constant supply of data to process.

Question 10

In the CPU what does the Arithmetic and Logic Unit (ALU) do? And what are the two parts of the ALU?

Answer 10

This is were the CPU actually carries out the maths and logic on the data (processes it).
It has two parts:
Arithmetic part, which performs calculations on the data, e.g. 3 + 2 = 5
Logic part – which deals with logical operations such as is True / False / Equal to / Greater than etc.

Question 11

Who was John Von Neuman?

Answer 11

Born in 1945, mathematician, invented the architecture for computers

Question 12

Assembly Language and the Von Neumann Architecture
What does it mean?
ADD

Answer 12

Add numbers together

Question 13

Assembly Language and the Von Neumann Architecture
What does it mean?
SUB

Answer 13

Subtract numbers

Question 14

Assembly Language and the Von Neumann Architecture
What does it mean?
STA

Answer 14

Store a value

Question 15

Assembly Language and the Von Neumann Architecture
What does it mean?
LDA

Answer 15

Load a value

Question 16

Assembly Language and the Von Neumann Architecture
What does it mean?
BRA

Answer 16

Branch to a different part of the programme, often used to repeat code

Question 17

Assembly Language and the Von Neumann Architecture
What does it mean?
OUT

Answer 17

Output a value (after processing)

Question 18

Assembly Language and the Von Neumann Architecture
A CPU performs each instruction using a ‘register’, a tiny memory location (memory store)
What does it mean?
ACC

Answer 18

The Accumulator

Question 19

Assembly Language and the Von Neumann Architecture
What does it mean?
PC

Answer 19

The Programme Counter

Question 20

Assembly Language and the Von Neumann Architecture
A CPU performs each instruction using a ‘register’, a tiny memory location (memory store)
What does it mean?
MAR

Answer 20

The Memory Address Register

Question 21

Assembly Language and the Von Neumann Architecture
A CPU performs each instruction using a ‘register’, a tiny memory location (memory store)
What does it mean?
IR

Answer 21

The Instruction Register

Question 22

Assembly Language and the Von Neumann Architecture
A CPU performs each instruction using a ‘register’, a tiny memory location (memory store)
What does it mean?
MDR

Answer 22

The Memory Data Register

Question 23

What do we mean by LMC - a programme that simulates how a CPU works?

Answer 23

The Little Man Computer

Question 24

What is the LMC and what does the LMC simulate?

Answer 24

The Little Man Computer simulates how ‘Low Level Programming Code’ is used to operate the CPU.

It mimics how data and instructions are ‘Fetched’, ‘Decoded’ and organised into the CPU registers (small temporary memory stores)and ‘Executed’ using the accumulator.

Question 25

What do we mean when we talk of the brain of the computer?

Answer 25

the CPU

Question 26

What are we talking about here?
“The speed of the Fetch-Decode-Execute cycle is determined by the CPU’s clock chip.

This chip uses a vibrating crystal that maintains a constant rate.”

Answer 26

Clock speed

Question 27

What is clock speed measured in?

Answer 27

hertz (Hz) which is the amount of cycles per second.
clock speed of 500Hz means 500 cycles per second.

Current computers have CPU clock speeds of 3GHz which means 3 Billion cycles per second

Question 28

It is possible to increase the clock speed for a CPU.

This is known as what?

Answer 28

overclocking.

In theory, if the clock is faster then the CPU can perform more calculations and perform faster.

Question 29

What is the problem with increasing the speed of a CPU by overclocking?

Answer 29

Problem is that CPUs get hot the more work they do – so overclocking is dangerous without the appropriate heat management.

Question 30

A computer system will have two types of storage:

what are they?

Answer 30

A computer system will have two types of storage:
Primary – Cache, RAM (aka main memory), ROM
Secondary – Hard Disk, Flash Drive

Question 31

What are four features of Primary storage? (compared to secondary storage)

Answer 31

1) Most Primary Storage is volatile (temporary).
2) Primary Storage is expensive and smaller.
3) Primary storage is smaller in capacity (L2 Cache is only 2MB
4) Primary storage is closer to the CPU and/or is integrated onto it and therefore is faster.

Question 32

What are four features of Secondary storage? (compared to Primary storage)

Answer 32

1) All secondary storage is (non-volatile) permanent
2) Secondary storage is usually cheaper and large
3) Secondary Storage is bigger in capacity
4) Secondary storage connects to the CPU via cables and therefore is slower

Question 33

How fast is cache memory?

Answer 33

Cache memory has read speeds similar to the CPU and is therefore much faster than RAM.

Question 34

CPUs work faster than RAM so how do computers speed things up?

Answer 34

They use the cache

So, to improve efficiency the CPU’s ‘Control Unit’ will look first in the cache for the next instruction to see if it has already been copied which reduces the time taken to access data.

If the cache is larger, it is more likely that the next required instruction has already been transferred from the RAM to the CPU thus improving process time.

Question 35

CPUs are very fast

How do you make them go faster?

Answer 35

So if CPUs can’t go faster, the solution its to add 2 CPU chips, or 4, or 8, etc).

These chips are called ‘cores’.

Question 36

What are the two ways in which a CPU with more than one core can process more instructions in the same time period:
?

Answer 36

They can carry out Parallel Processing which is when the same program can have two instructions processed at the same time.

More cores also enables Multi-Tasking where each core can each process two different programs’ instructions at the same time.

Either way, more cores means more instructions being processed at once.

Question 37

What are embedded systems?

Answer 37

In devices such as phones or cameras