Types of registers and their functions

 Types of registers and their functions

a. Memory Data Register (MDR)

This is the register that contains the data to be stored in the computer memory or the data fetched from memory and ready to be processed by the CPU. It acts like a buffer and holds

anything that is copied from the memory ready for the processor to use it.

b. Current Instruction Register (CIR)

This is part of the CPU’s control unit that stores the instruction currently being executed or decoded.

c. Memory Address Register (MAR)

This is the CPU register that either stores the memory address from which data will be fetched to the CPU or the address to which data will be sent and stored.

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

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

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

(g)     FPRs (Floating Point Registers): They store floating point numbers.

(h)   Constant Registers holds read – only values such as one.

(i)   Special Purpose Registers: They hold program statements.

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

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

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

Differences between Register and Main Memory

Data-Fetch-Execute cycle

Fetch execute cycle is the very basic way a computer works. All commands are executed through the running of this cycle. The cycle itself has very few commands, however, when linked up together it is possible to create a large program or even an operating system.

The cycle contains 3 main parts

Fetch the instruction

Decode the instruction

Execute the instruction

The following are factors affecting the Speed of Data Transfer

Bus Speed

Bus Width

Medium of Storage

Data transfer medium