1.1.1 Processors, input, output and storage Flashcards
Computer
A computer can process an input from a user in order to reach an output
CPU
Central processing unit
What does a CPU design depend on
What it is being used for
e.g. phone is smaller than a PC and is battery powered without a fan so it needs a smaller CPU with less functions
Components of a CPU
Control Unit
Buses
Arithmetic Logic Unit
Designated Registers
Control unit
Processes instructions for the CPU
Buses
Move signals around
Consist of connectors that transfer signals between components
8/16/32/64 lines
3 types of bus
Address bus - where it is going ; CPU to RAM
Data bus - carries the data around ; both ways
Control bus - controls data instructions ; both ways
Arithmetic logic unit
Carries out arithmetic and outputs - stores results in the accumulator
CIR
Current instruction register
Holds the current instruction that is being followed
PC (register)
Program counter
Memory address of the next instruction
MAR
Memory address register
Holds the address of where data is being read/written
MDR
Memory data register
Holds data between processor and memory
AC
Accumulator
Stores the result of logical calculations
What must you call registers by?
Their full names - NO ACRONYMS
Fetch
CPU fetches data and stores in registers
- PC transfers address of next instruction to MAR
- Instruction from that address is carried to MDR
- Simultaneously PC value increases by 1
- Contents of MDR are transferred to CIR
Decode
- Instruction held in CIR is decoded
- Split into operand and opcode to define the type of instruction and acquire any additional data
- Passed to ALU
Execute
- Instruction is executed and result stored in accumulator or memory
Operand and opcode
opcode has the instruction
operand has the data and address.
Words
The equal units memory is divided into, usually 8/16/32/64 bits
Each has a separate memory address
Address bus
The width determines the maximum possible memory addresses (2 to the power of width addresses)
Hexadecimal machine code instruction
8 bits opcode - 6 instruction, 2 clarify what
8 bits operand
Factors affecting performance
Clock speed
Number of core
Cache memory
Buses
How does clock speed affect performance?
It increases the speed of the fetch/decode/execute cycle.
The faster clock speed the more instructions executed per second.
You can overclock if the clock speed is too high
How does the number of cores affect performance?
They can process more instructions simultaneously
Parallel processing - where multiple cores work on different elements of the same task to complete it quicker
Cache memory
A small amount of superfast memory that stores recent data and instructions
Level 1 cache smaller but faster, cores share level 2
More allows for better performance
How can buses affect performance?
A bigger address bus allows you to have more address locations, storing more data and instructions
Methods to improve the performance of a computer
Changing CPU for clock speed/ more cores/ more cache
More or faster RAM
Change graphics card
SSD (Solid state drive)
Pipelining
Overlapping stages of the F/D/E cycle to improve performance
One line is executed as the next is decided and the one after that fetched
Data is held in a buffer
Issues with pipelining
Conditionals from instructions you have executed may mean you now need different instructions, negating the gain by fetching and decoding others before.
Register definition
Small memory cells that operate at a higj speed. They store data and operations are carried out on data in them
Clock
An electronic device which generates signals, switching between 0 and 1. The clock speed is measured in Hz
Core
An independent processor able to carry out its own F/D/E cycle
