ICT (Computer Studies): Computer Data Conversion (2)

TYPES OF REGISTER

   (a)   MDR (Memory Data Register)

This is the register of a computer’s control unit that contains the data to be stored in the computer storage (e.g RAM), or the data after a fetch from the computer storage. It acts like a buffer and holds anything that is copied from the memory ready for the processor to use it.

The MDR is a two – way register because when data is fetched from memory and placed into the MDR, it is written to in one direction. When there is a write instruction, the data to be written is placed into the MDR from another CPU register, which then puts the data into memory.

    (b)   CIR (Current Interrupt Register)

It captures the value that is winning the interrupt arbitration. The CIR is updated at the beginning of an interrupt acknowledge bus cycle or in response to an update CIR command. The contents remain in the CIR until another interrupt acknowledge cycle or update CIR Command occurs.

   (c)    User – Accessible Register: The most common division of user – accessible registers is into data registers and address registers.

   (d)   Data Registers: They are used to hold numeric values such as integer and floating – point values.

   (e)    GPRs (General Purpose Registers): They can store both data and addresses.

   (f)     FPRs (Floating Point Registers): They store floating point numbers in many architectures.

   (g)   Constant Registers holds read – only values such as one, or pi.

   (h)   Special Purpose Registers: They hold program state

   (i)     Instruction Registers store the instruction currently being executed.

   (j)     Model – Specific Register (also known as machine – specific register) store data and settings related to the processor itself.

   (k)   Control and status register: It has three types which are program counter, instruction register and status word (PSW).

Exercises:

1.      What is MDR?

2.      What acts like a buffer in the register?

3.      What is CIR?

4.      What are the differences between data registers and general purpose registers?

5.      Name and briefly describe five types of registers.