The use of register organisation make the instruction shorter and faster hence the execution time will be reduce significantly. The use of register used by the processor globally classify into two types such as:-
- General purpose Register
2. Control and status Register
1. General Purpose Register :-
It is accessed by user which is accessed by the processor.
The register are said to be user visible register if these are used by the user or programmer during program development.
These register are accessed by the user to hold any value and the values can be changed from time to time during the execution.
These are 3 type such as :-
- Address Register
- Data Register
- Condition code Register
Address Register :-
It is define as the user visible registers, which always holds the address of memory or I/O process.
Hence the register always hold on negative value or positive value.
Data Register :-
The user visible register is said to be data register if it always stores or holds,, source operates or results.
It is capable of storing or holding both positive and negative values.
Condition code register:-
The user visible register, which stores the status flags of the processor are expensively thing is called an condition code register.
2. Control status Register:-
Other flag will set or reset every time during execution of user program control and status.
The register which are addressed by the processor only and used to execute user program and known as control and status register.
The control and status register are of 4 types :-
- PC (program counter):- It is define as the system register which holds the address of next instruction to be executed after the execution of current instruction is completed.
- IR (Instruction Register) :- It is define as the register which hold the current instruction fetch and read from the memory.
Whenever the processor reads instructions from memory it will be brought through database and will kept in IR from execution.
- MAR (memory address Register) :- The register is said to be MAR if it holds the address of memory locations to be accessed by the processor.
The value of PC is copied into MAR and the address will be send to the memory through the address bus.
- MBR (memory buffer register) :- The control and status register , which holds the data read from memory or data to be written into memory known as MBR or MDR.
The register may hold either operand values or instruction.
The register is directly connected to the database for sending or receiving data through the data bus