1.1 Systems Architecture (OCR GCSE Computer Science)

What does CPU stand for?

The Central Processing Unit.

What is the CPU?

The brain of the computer system.

What does the CPU do?

Process the data and instructions that make the computer system work.

What does the processing power of a CPU depend on?

It's:

-Clock speed

-Number of cores

-Cache size

What does the CPU architecture describe?

The main components of the CPU, their interaction with one another, and their interaction with other parts of the computer system.

How many main parts does a CPU have?

3

What are the names of the 3 main parts of a CPU?

-The control unit (CU)

-The arithmetic logic unit (ALU)

-The cache

Which main part of the CPU has the overall control of the CPU?

The control unit (CU)

What is the main job of the control unit (CU)?

To execute program instructions by following the fetch-decode-execute cycle.

"The Control Unit (CU) controls the flow of data __________ and __________ of the CPU."

"inside"

"outside"

The Control Unit controls the flow of data inside the CPU to where?

To the registers, the ALU and the cache.

The Control Unit controls the flow of data outside the CPU to where?

To the main memory and input/output devices.

What does ALU stand for?

The Arithmetic Logic Unit

What does the ALU do?

All the calculations and comparisons - sImple addition and subtraction, compares the size of numbers and can do multiplications and divisions using repeated addition and subtraction.

What register does the ALU contain?

The accumulator.

What type of operations does the ALU perform?

Logic operations such as AND, OR and NOT and binary shifts.

What is the cache?

The cache is very fast memory in the CPU.

"Cache is _____________ than registers, but _____________ than RAM"

"slower"

"Faster"

"The cache stores ____________________ used data"

"regularly"

Why does the cache store regularly used data?

So that the CPU can access it quickly the next time that it is needed.

When the CPU requests data, where does it first check?

The cache.

When the CPU requests data, and the data is not in the cache, where does it check next?

The RAM.

"Compared to RAM and secondary storage, caches have a very low _____________ and are ________________."

"capacity"

"expensive"

What are the three levels of cache size?

L1, L2 and L3.

"Compared to other cache sizes, L1 is the _________________ but has the lowest _____________."

"quickest"

"capacity"

"L2 cache size is _____________ than L1, but can hold _________."

"slower"

"more"

"L3 cache size is ____________ than L2, but can hold _________."

"slower"

"more"

The registers that the CPU contains do what?

Temporarily hold tiny bits of data needed by the CPU.

An advantage of registers is that they are...

Super quick to read/write, way quicker than any other form of memory.

When did Von Neumann come up with his CPU architecture?

1945

What does the Von Neumann architecture describe?

A system where the CPU runs programs stored in memory. Programs consist of instructions and data which are stored in memory addresses.

What is the function of the program counter (PC)?

To hold the memory address of the instruction for each cycle.

What is the function of the accumulator?

To store the immediate results of calculations in the ALU.

What is the function of memory?

To hold the program instructions and the program data.

Other than the accumulator, what other two registers are present in the CPU?

The Memory Address Register (MAR) and the Memory Data Register (MDR).

What is the function of the MAR?

To hold any memory address about to be used by the CPU. The address may point to data, or a CPU instruction.

What is the function of the MDR?

To hold actual data or instructions, which may have been fetched from the memory, or be waiting to be written to memory.

Which cycle do CPUs follow?

The fetch-decode-execute cycle.

What does the fetch instruction do?

1. Copies the memory address from the program counter to the MAR.

2. Copies the instruction which is stored in the MAR address to the MDR.

3. Increments the program counter to point to the address of the next instruction.

What does the decode instruction do?

The instruction in the MDR is passed to the Instruction Register where it is decoded by the CU and the CU might prep for the next step by loading values into the MDR/MAR etc.

What does the execute instruction do?

The instruction is carried out. If data needs to be saved, it is stored in the accumulator.

What does the instruction register do?

Used in the decode part of the fetch-decode-execute cycle. The control unit looks up in the instruction set what the instruction means so that the CPU can then execute it.

What is an embedded system?

A smaller device used to perform a specific task within a larger device, eg washing machine.

Why is an embedded system also called a real-time system?

Embedded systems must ensure an immediate response in order for the system to react to different situations, eg airbags in a car must deploy as soon as a collision is detected.

How is clock speed measured?

The clock is a vibrating quartz crystal. The faster it vibrates, the faster instructions are processed. Rates of 3-4GHz are common for standard computers.

State 3 methods of cooling the CPU

Heat sink

Fan

Water cooling

What impact does doubling the number of cores have?

Doubling the number of cores can increase processing speeds, as each processor can work on different tasks at the same time.

What is parallel processing?

Parallel processing occurs when multiple cores work on the same program at the same time.

What is multitasking?

Multitasking is when multiple cores can work on different programs at the same time.

Describe what is meant by a 3.2GHz CPU.

A 3.2GHz CPU has a clock speed of 3.2GHz. This gives the number of instructions which can be processed each second. A 3.2GHz processor can complete 3.2 billion processing cycles per second.

CPU

central processing unit

the purpose of the CPU

to process all of the data and instructions that make the computer system work

what the CPU does

fetch, decode and execute instructions

registers (in the CPU)

memory address register (MAR), memory data register (MDR), program counter (PC), accumulator

what registers are

small amount of memory on the chip

the purpose of the memory address register (MAR)

stores the location in memory to be used by the CPU and holds the address of where data is fetched or stored

the purpose of the memory data register (MDR)

holds data to be fetched from or to be written to the memory

the purpose of the program counter (PC)

holds the address of the next instruction

the purpose of the accumulator

holds the results of calculations

the components of the CPU

the arithmetic logic unit (ALU), the control unit (CU) and the cache

the purpose of the arithmetic logic unit (ALU)

performs addition and subtraction calculations, and logical decisions

the purpose of the control unit (CU)

decodes instructions and sends signals to control how data moves around the CPU

the purpose of the cache

provides fast access to frequently accessed instructions and data without having to go to the main memory (RAM)

factors affecting the speed of the CPU

clock speed, cache size, number of cores

clock speed

the number of cycles per second, measured in hertz (Hz)

cache size

the size of the cache which stores recently fetched instructions or data so that it can be fetched from the cache, which is much quicker than going back to the main memory (RAM)

embedded systems

computer systems with a dedicated function within a larger mechanical or electrical system

examples of embedded systems

washing machine, coffee maker, engine management system

the function of washing machines

to wash the clothes inside by a sequence of fill, turn, drain cycles which is controlled by a user-selected wash program

the function of a coffee maker

to make coffee by a sequence of water outputs which is controlled by a user input

the function of a engine management system

to control the fuel supply and the ignition of the combustion process, making the engine more efficient and less polluting

the first part of the fetch-decode-execute cycle of the CPU

copy the memory address from the program counter to the MAR and the instruction stored in the MAR address to the MDR

the second part of the fetch-decode-execute cycle of the CPU

decode the instruction in the MDR via the CU and prepare for next step (e.g. load values into the MAR or the MDR via the CU)

the third (final) part of the fetch-decode-execute cycle of the CPU

perform the instruction (e.g load data from memory, write data to memory, do a calculation or logic operation via the ALU, change the address in the PC, halt the program)

Input

This is the stage where data is entered into a computer system

Process

This is the stage where data is manipulated by the CPU

Output

This is the stage where you get to see the processed data

Program

This is software and it provides the CPU with instructions

Storage

This stage happens if data needs to be kept for use at a later date

Embedded

A specialized type of computer that performs one specific task

Hardware

Parts of the computer that you can physically touch, see or pickup

Register

A very fast type of memory located within the CPU which holds a tiny amount of information

Control Unit

This is the part of the CPU which controls the way that data moves around the CPU

Clock

This is a tiny quartz crystal inside the CPU which ticks at a steady speed. During each tick one instruction can be processed.

Cache

A very fast type of memory which can hold more data than a register but less than RAM

ALU

This part of the CPU does all of the calculations and comparisons

RAM Memory

This is where the CPU fetches program instructions from

Executes

The CPU fetches instructions from memory then decodes them and then .......... those instructions

The Program Counter

The software that is running, updates this with the address of the next instruction to be fetched

A stored program computer

Another term for the Von Neumann architecture

The Memory Address Register

The address of the data or instruction being accessed by the CPU is temporarily stored here

The Memory Data Register

The register which temporarily stores an instruction or data on its way to or from RAM

The Accumulator

The register used to temporarily store the results of calculations

Overclocking

Making the CPU clock run faster than its default settings

Core

A self-contained processing unit inside the CPU

Parallel processing

Executing several instructions at once using multiple cores

Heatsink

A piece of hardware included to remove excess heat from the CPU

Quad Core

A CPU with four cores

Fetch

The part of the FDE cycle where instructions are retrieved from main memory to the CPU

Decode

The stage where instructions are checked and validated