Process System of Computer System Architecture

What is Register Files?

Register computer memory has a fast memory.  This memory is used to store data in the computer, to perform instructions.  

A register is a set of flip-flops, there are many cables inside the flip-flop, and each flip-flop cable stores one bit of information.

What is Computer Register ?

As we know register is a type of memory and it is used by the CPU to store data, transfer, and perform any instruction quickly.  

The register used by the CPU is called the process register. The process register holds the instruction.

The computer needs a process register when the computer has to manipulate some data and when it has to hold the memory address of a register. 

Below is a list of some registers that are commonly used on computers.

Data Register - This register is of 16 bits and it holds the memory operation.

Address Register - This register is of 12 bits and it holds the memory address.

Accumulator - This register is of 16 bits and this is the processor of the register.

Instruction Register - This register is of 16 bits and it holds the instruction code.

Program Counter - This register is of 12 bits and it holds the address of the instruction.

Temporary Register - This register is of 16 bits and it holds temporary data.

Input Register - This register is of 8 bits and it carries the input character.

Output Register - This register is of 8 bits and it carries the output character.

Register and memory configuration of a basic computer

 Diagram

The memory unit has a capacity of 4096 words and each word contains 16 bits.

The data register consists of 16 bits and it holds the operand in the memory location.

The memory address register is of 12 bits and it holds the address in the memory location.

The program counter is of 12 bits and it holds the next instruction of the address to raid the memory after the current instruction is executed on the memory.

The accumulator register is a general-purpose processing register.

A temporary register is used to hold temporary data at the time of processing.

The input register holds the input character provided by the user.

The output register holds the output, after processing the input data.

Complete Instruction Execution

The register is involved in every instruction cycle are,

Memory Address Register (MAR)

It is connected to the address line of the system bus.  It specifies read and writes operations on the memory address. 

Memory Buffer Register (MBR)

It is connected to the data line of the system bus.  It contains the value to be stored in memory or the last value read from the memory.

The Program Counter (PC)

Program counter holds the address of the next instruction to be fetched.

What is Instruction Cycle ?

Each step in the instruction cycle can be broken down into a sequence of elementary, micro-operations.  Below is a diagram of the instruction cycle.

The indirect cycle always follows the execute cycle.

The interrupt cycle always follows the fetch cycle.

And after that the fetch and execute cycle, the next cycle depends on the state of the system.

Let's know about fetch, decoder, and execution. 

Fetch

In this phase, the instruction is fetched from the memory address.  Which is stored in the PC and instruction register.  And when the fetch operation is over, the PC points to execute another instruction.

Decoder

In the decoder phase, the encoded instruction present in the instruction register (IR) is interpreted by the decoder.

Execution

In the execution phase, the control unit sends the decoded information in the form of control signals to the functional unit of the CPU.  After this, the CPU completes the task according to the need for instruction.

Design of Control Unit

The Control unit is classified into two parts based on its design,

1.  Hardware Control
2.  Microprogrammed Control

Hardware Control

The hardware control of the control unit is organized by gates, flip-flops, decoder, and other digital circuits.

Hardware control is made up of two decoders, a sequence counter, and a number of logic gates.

In this, an instruction emanating from the memory unit is kept on the instruction register.

Microprogram Control

The organization of microprogram control is implemented using a programming approach.

In microprogrammed control, micro-operations are performed by executing a program with microinstructions.

The following image shows the block diagram of a microprogrammed control organization.

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