Registers, System Clock and Coprocessors


Register is a small high-speed memory inside CPU. It is used to store temporary results. CPU contains a number of registers. Each register has a predefined function.

Register size determines how much information it can store. The size of registers is in bytes. Each byte can store one character of data. A register can be of one, two, four or eight bytes. Bigger size of register increases the performance of CPU.

Different registers in Intel-8086 family processor are as follows:

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1. Accumulative Registers

Accumulative registers are used in mathematical and logical operations. These registers are part of ALU. There are four types of accumulative registers called EAX, EBX, ECX and EDX.

The size of these registers can be 1 to 4 bytes. The two-byte data registers (AX, BX, CX, DX) contain two parts of 8-bit size. These parts are separately accessible. The lower-order bytes are designated as AL, BL, CL, and DL. The high-order bytes are designated as AH, BH, CH, and DH.

2. Stack Control Register

A stack is set of memory location in which data is stored and retrieved in an order. This order is called Last-In-First-Out (LIFO). The data item stored at the top of stack is retrieved before retrieving the item below it.

Stack control registers are used to manage stack in computer. Two special registers SP and BP are used for this purpose. DI, SI, SP & BP can either be used as 2 byte register or 4 byte registers. The names of 4-byte stack control registers are EDI, ESI, ESP and EBP.

3. Instruction Pointer Register

Instruction pointer register is used to store the memory location of the next instruction to be executed. It works along with the segment registers.

4. Address or Segment Registers

Address or segment register is used to store the memory location of the instruction that is being executed. This is a group of 4 or 6 registers of two bytes named CS, DS, ES & SS, FG, GS. These registers are used with either the IP register or two index registers Dl and SI.

5. Flag Registers

Flag registers are used to indicate a particular condition. The size of flag register is one or two-byte. Each byte of flag registers is further divided into eight bits. The data in flag register is stored in 8 distinct bits. Each bit of the flag register indicates a flag or condition. Some flag registers are Zero flag, Carry flag, Parity flag Sign flag and Overflow flag.

System Clock

System clock is an electronic component. It generates electric signals at a fast speed. It controls all functions of the computer using clock ticks. Computer clock can tick from 100 million to 1000 million times in one second.

The speed at which the CPU executes instructions is called clock speed or clock rate. This speed depends on the model of the computer. Clock speed is measured in MHz. Clock speed tells us how much time a CPU takes to execute each instruction. CPU takes from 1 to 6 clock ticks to execute one instruction.

Heat Sinks & Heat Pipes

The heat sink is a small ceramic or metal component used to absorb and ventilate the heat produced by electrical components of the computer. In some computers, it is part of the processor chip. It can also be installed on top or the side of the chip. The size of heat sink is large and it occupies more space. So heat pipes are used to absorb heat in notebook computers.


A coprocessor is a special-purpose chip mounted on a processor board that can be installed into a computer. It is designed to handle common functions quickly and efficiently, and so expand on doing some of the processing of the chip. This frees up the CPU for other processing

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