1.1.1

Question 1

Control unit

Answer 1

Controls and coordinates all activities of the CPU.
Directs flow of data between CPU and other devices.

Question 2

Arithmetic logic unit (ALU)

Answer 2

Carries out arithmetic and logic calculations.
Arithmetic operations are on fixed and floating point numbers: ADD/ SUBTRACT/ MULTIPLY / DIVIDE
Boolean logic operations: Comparison /AND /OR/ NOT/ XOR

Often uses general purpose registers to temporarily hold results of calculations such as accumulator.

Question 3

Registers

Answer 3

Are small storage locations used to hold data temporarily.
They have high read and write speeds.

Question 4

Program counter (PC)

Answer 4

Stores the address of the next instruction.
Has a very close relationship to MAR, at the start of every fetch, decode, execute cycle address held in PC is stored in MAR.

Question 5

Memory address register (MAR)

Answer 5

Temporarily holds the address of the memory location which needs to be fetched or set from main memory that the processor needs to access.

Question 6

Memory data register (MDR)

Answer 6

Used to temporarily store data which is read from/ written to memory.
Sometimes known as buffer register (MBR)
All data to and form memory must travel down data bus and pass through MDR.

Question 7

Current instruction register (CIR)

Answer 7

Area where the current instruction is being carried out. The operation is divided into operand and opcode.

Question 8

Accumulator

Answer 8

Stores the results of the calculations made by the ALU.

Question 9

Interrupt register

Answer 9

Generates and detects interrupts.

Question 10

Assembly code

Answer 10

Uses mnemonics to present instructions, for instance SUB represents subtraction. This is a simplified way of representing machine code, easier to remember than binary.

Question 11

Assembly code mnemonics

Answer 11

Simplified

Question 12

Buses

Answer 12

Communication paths between the CPU, memory and other components.

Question 13

Address bus

Answer 13

A one directional bus that transmits memory addresses that are used as operands in programming instructions, so that data can be retrieved from main memory.

Question 14

Data bus

Answer 14

A bi-directional path for moving data and instructions between system components.

Question 15

Control bus

Answer 15

A bi-directional bus to transmit command, timing and specific status information between system components

Question 16

Control bus

Answer 16

A bi-directional bus to transmit command, timing and specific status information between system components.

Question 17

Fetch decode execute (FDE)

Answer 17

PC
MAR

Address Bus
Memory
Data bus
MDR
CIR
Decode Uni

Question 18

Fetch

Answer 18

1. The address of the next instruction is copied from the PC to the MAR
2. The fetch signal is sent across the control bus. The content of the MAR are transferred across the address bus.
3. The contents of the memory location stored in the MAR are sent across the data bus and stored in the CIR
4. the PC increments by 1

Question 19

Decode

Answer 19

1. The contents of the CIR are sent to the CU and divided.
   The Opcode tells you the instruction to be carried out and the operand stores the address of any data which might be needed.
2. The operand is sent to the MAR and the data is fetched from memory and stored in the MDR

Question 20

Execute

Answer 20

The appropriate opcode is carried out on the operand.

Question 21

How does a program branch happen and what is the result?

Answer 21

Due to an if statement, function, procedure call or loop. Results are that the next instruction held in the PC is not carried out.

Question 22

Clock speed

Answer 22

Indicates the number of instructions the CPU can process per second, unit is hertz.
The clock speed is determined by the system clock. This is an electronic device which generates signals, switching between 0 and 1.

Question 23

Advantages and disadvantages of increasing clock speed

Answer 23

you can carry out more instructions in a given time; improved performance

more heat generated meaning computers must be cooled (either with heat sync/fan or water/oil cooling)

Question 24

Multiple cores

Answer 24

A core is an independent processor, which is able to compile its own fetch-execute cycle.
The more cores a computer has, the more fetch-execute cycle it can carry out at any given time.
Dual-core processor has two processors linked together in the same integrated circuit.
Quad-core computer has four linked processors (each with its own registers, ALU, accumulator and control unit)

Question 25

Advantages and disadvantages of multiple cores

Answer 25

May speed up processing.

Having double the number of cores in a system doesn’t mean double the performance because some cores could have a lower clock speed due to the temperature and size, so some speed can be lost as cores try to communicate with each other.
Programs are not utilised to take advantage efficiently of this design.

Question 26

Cache memory

Answer 26

Cache is a small amount of fast memory, which is directly connected to the CPU that can fetch recently used data.
Instructions fetched from main memory are copied to the cache, so if required again, they can be accessed quicker.
As cache is filled up, the unused instructions are replaced to make use of recent data to be made more accessible.

Question 27

Cache memory advantages and disadvantages

Answer 27

Much quicker to access than main memory (RAM), less time fetching data.

Its expensive.
If the computer is turn off, the data stored in them is not saved it gets destroyed.

Question 28

Pipelining

Answer 28

Is the process of completing the fetch, decode, and execute cycles of three separate instructions simultaneously, holding appropriate data in a buffer in close proximity to the CPU until it’s required.
While one instruction is being executed, another can be decoded and another fetched.

Question 29

Advantageous and disadvantageous of pipelining

Answer 29

More efficient meaning it can do the fetch-execute cycle simultaneously.
Pipelined CPU’s works at higher clock frequencies than the RA; increases overall performance.

If you have branching instructions it will make the pipelining inefficient because it would have to flush the instructions.
Designing of the pipelined processor is complex.
The throughput of a pipelined processor is difficult to predict.

Question 30

Von Neumann

Answer 30

• (Single) Control Unit
• (Single) Arithmetic Logic Unit
• (Special) registers within CPU
• Instructions and Data stored in same area of
  memory
  Is when memory is shared between instructions and data and they also share the same buses and can only fetch data and instructions at once.
  e.g. PC’s and servers.

Question 31

Harvard

Answer 31

Stores data and instructions in physically separate memory locations.
Instructions and data are each served by their own buses.

e.g. Speech and image processing systems/ Mobile communication systems.

Question 32

Difference between Harvard and Nuemann

Answer 32

Question 33

improving computer performance

Answer 33

A newer CPU may have a faster clock speed and so execute more instructions per second. It may have multiple cores and so be able to execute several programs simultaneously (or one in parallel). It may have more cache meaning comparatively slower RAM can be accessed less frequently.
More RAM means more programs can be open simultaneously
without the need to use much slower virtual memory.
- Adding a graphics card will speed up the rendering of 3D graphics as GPU has specialist instructions and can apply the same instruction to multiple pieces of data simultaneously.
- The slower the secondary storage the longer it takes to load files/program/data. A faster secondary storage device can improve this. May choose to use flash memory (i.e. SSD)
- OS makers often release updates and some of these will improve performance.
- Some lighter weight operating systems use fewer system resources allowing the system to devote more to running the user’s applications.
- A fragmented HDD runs slowly as time is spent finding parts of the files. This is reduced by defragmenting and storing the parts of the file contiguously.
- Malware can slow down a computer. Removing it will improve performance.

Question 34

features not in von nuemann but are in contemporary

Answer 34

Two separate areas of memory…
…one for instructions & one for data./instructions and
data can be accessed concurrently.

Different (sets of) buses…
… one for instructions & one for data./ instructions and
data can be accessed concurrently.

Pipelining…
…whilst an instruction is being executed the next can
be decoded and the subsequent one fetched.