Computer CPU Registers

Different CPU register :

register
cpu register
               A register is a group of memory elements that work together as a unit. It can store one bit of information. The simplest registers do nothing more than store a binary word;others modify the stored word by shifting its bits left or right or by performing other operations to be discussed in this article.

Accumulator(AC):

        An accumulator(AC) is a buffer register that store the result after the computation,It is a 16 -bits register and determines the largest real integer number that can be processed in a computer.

Flag:

Status register which is a special purpose register of CPU is known as flag-register or condition code.It holds 1-bit flags to indicate certain condition that arises during arithmetic and logical operations.

Program Counter (PC):

Program counter(PC) store the address of the next instruction.Program counter at any point of time holds the address of the next instruction in the  program.At the beginning of execution,It points to the address of the first instruction.This register goes through a counting sequence and directs computer to read instructions sequentially from the memory.

Instruction Register(IR):

Holds the current instruction after it has been fetched from the memory and so on. It consists of an op-code of 4 data bits an address or 12-bits,so Instruction Register(IR) is a 16-bits register.

Memory Address Register(MAR):

Memory Address Register(MAR) at any time contains the address of current instruction being executed.The process proceeds like this- read cycle initiated and PC incremented by one. Since MAR is required to address memory only,it is a 12-bits register.

Memory Buffer Register(MBR):

Memory buffer register (MBR) is a 16-bits register the store the data temporarily as it is.Transferred back and forth between the memory.Read/write signals are held here.

General Purpose Register(GPR):

There are 9 General Purpose Register (GPR) which ware used to store intermediate result obtained during and arithmetic operations.They are numbered 1,2,3 ....9 Each register is 8 digits log and can hold one word. 

Register usage:

The number of registers available on a processor and the operations that can be performed using those registers has a significant impact on the efficiency of code generated by optimizing compilers. The Strahler number of an expression tree gives the minimum number of registers required to evaluate that expression tree.

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