Basic of Computer Organisation

7/30/2019 Basic of Computer Organisation

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Basic Computer Organization:

Microprocessor Organization -

Processor, Register, Clock


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4 main components:

1. Microprocessor

2. Memory

3. CPU Memory I/O Architecture

4. Instruction cycle


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Knowledge of these components and their

operation (interaction) offers insight into

system bottlenecks, alternate pathways,

magnitude of system failures, andopportunities for performance enhancement


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The functions performed by the CPU:

Fetch instructions

Fetch data

Process data

Write data

Organizational requirements that are derived fromthese functions:

ALU

Control logic

Registers

Internal CPU bus


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ALU: computation or processing of data (in

the internal CPU memory only)

Control logic: controls movement of data and

instructions into/out of the CPU; andcontrols the operation of ALU

Registers: internal temporary memory

Internal CPU bus: Means to move data and

instructions in and around the CPU


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Memory in the computer system can be

viewed in a hierarchy. (fig 3.3)

Memory in CPU: registers.

2 main roles of registers:

1. User-visible registers

2. Control and status registers


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To minimize usage of main memory, controlled bymachine or assembly-language program.

Can be categorized into 4 main categories: General purpose

Data

Address

Condition codes


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General purpose

Can be assigned a variety of functions

Ideally, they are defined orthogonally to the operationswithin the instructions

Data These registers only hold data


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Address

These registers only hold address information

Examples: general purpose address registers, segmentpointers, stack pointers, index registers

Condition codes Visible to the user but values set by the CPU as the result

of performing operations

Example code bits: zero, positive, overflow

Bit values are used as the basis for conditional jump

instructions


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General purpose registers maximize flexibility

in instruction design

Special purpose registers permit implicit

register specification in instructions reduces register field size in an instruction

No clear best design approach


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More registers permit more operands tobe held within the CPU -- reducingmemory bandwidth requirements to someextent

More registers cause an increase in thefield sizes needed to specify registers inan instruction word

Locality of reference may not support toomany registers

Most machines use 8-32 registers (doesnot include RISC machines)


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Address registers should be wide enoughto hold the longest address address!

Data registers should be wide enough to

hold most data types Would not want to use 64-bit registers ifthe vast majority of data operations used16 and 32-bit operands

Related to width of memory data bus Concatenate registers together to store

longer formats


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These registers are used during the fetching,

decoding and execution of instructions

Many are not visible to the user/programmer

Some are visible but can not be (easily)modified


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Program counter

Points to the next instruction to be executed

Instruction register Contains the instruction being executed

Memory address register A special register containing the address of a

word currently required


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Memory data/buffer register

Register of a computer's control unit thatcontains the contents of a register to fetch orstore from or to the computer storage.

Program status word(s) Superset of condition code register Interrupt masks, supervisory modes, etc. Status information


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Basic of Computer Organisation