Thursday, August 30, 2012

What is Registers in Computer Architecture


As the instructions are interpreted and executed by the CPU, there is a movement of information between the various units of the computer system. In order to handle this process satisfactorily, and to speed up the rate of information transfer, the computer uses a number of special memory units, called registers. These registers are used to hold information on temporary basis, and are part of the CPU (not main memory).
The length of a register equals the number of bits it can store. Hence, a register that can store 8 bits is normally referred to as 8-bit register. Most CPU sold today, have 32-bit or 64-bit registers. The size of the registers is sometimes called the world size. The bigger the world size, the faster the computer can process a set of data. With all other parameters being same, a CPU with 32-bit registers, can process data twice as fast as one with 16-bit registers.

Registers in computer

Although, the number of registers varies from computer to computer, there are some registers, which are common to all computers. The functions of these registers are described below.


Memory Address Register (MAR)

- It holds the address of the active memory location. It is loaded from the program control register, when an instruction is read from memory.

Memory Buffer Register (MBR)

- It holds the contents of the memory world read from, or written in, memory. An instruction world placed in this register is transferred to the instruction register. A data word placed in this register is accessible for operation with the accumulator register, or for transfer to the I/O register.A word to be stored in memory location must first be transferred to the MBR, from where it is written in memory.

Program Control Register (PC)

- It holds the address of the next instruction to be executed Normally, the instructions of a program are stored in consecutive memory location, and read and executed in sequence, unless a branch instruction is encountered. A branch instruction is an operation, which calls for a transfer to a non-consecutive instruction. The address part of a brands instruction is transferred to the PC register, to become the address of the next instruction.

Accumulator Register (A)

- It holds the data to be operated upon, the intermediate results and the results of processing. It is used during the execution of most instructions. The results of arithmetic operations are returned to the accumulator register, for transfer to main memory, through the memory buffer register. In many computers, there are more than one accumulator registers.

Computer Architecture in Computer and Registers

Instruction Register (I)

- It holds the current instruction, which is being executed. As soon as the instruction is stored in this register, the operation part and the address part of the instruction are separated. The address part of the instruction is sent to the MAR. While its operation part is sent to the control unit, where it is decoded and interpreted, and ultimately command signals are generated to carry out the task specified by the instruction.

Input/output Register (I/O)

-It is used to communicate with the input/output devices. All input information, such as instructions and data, are transferred to this register by an input device. Similarly, all output information, to be transferred to an output device, is found in this registers.

Name of Register
Memory Address(MAR)
Holds the address of the active memory location
Memory Buffer(MBR)
Holds information on its way to and from memory
Program Control(PC)
Holds the address of the next instruction to be executed
Accumulators results and data to be3 operated upon
Holds an instruction, while it is being executed.

Communicates with the I/O devices

What is instruction sets in computer architecture

Every CPU has built-in-ability to execute a set of machine instructions, called instructions set. Most CPUs have 200 or more instructions (such as add, substract, and compare) in instruction set. The machine language designed for a processor (CPU), is based on the list of instructions supported by the CPU in its instructions set. Since each processor (CPU).is based on the list instructions supported by the CPU in its instructions set, Since each processor has a unique instruction set, machine language programs written for one computer will generally not run on another computer, with a different CPU.
What is Instruction Sets in Computer

CPUs made by different manufacturers have different instructions sets. In fact, different CPU models of the same manufacturer also often have different instructions sets. However, manufacturers tend to group their CPUs into “families”, which have similar instructions sets. When a new CPU is developed, it it ensured that its instructions set includes all the instructions in the instruction set of its predecessor Crumples some new ones. This manufacturing strategy is known as upward compatibility, and the new CPU is said to be upward compatible with its predecessor. This feature allows software written for a computer with a particular CPU, to work on computers with newer processors of the same family. In turn, it allows the users of these computer systems to easily upgrade their system, without worrying about converting all their existing software.NSK2VZ4KNRW6

Wednesday, August 29, 2012

What is central processing unit (CPU) how it is work

The CPU is the brain of a computer system. All major calculations and comparisons performed by a computer are carried out inside its CPU.
 The CPU is also responsible for activating and controlling the operation of other units of the computer system. Hence, no other single component of a computer determines its overall performance ,as much as the CPU, In order to be able to quickly evaluate any computer capabilities it is important to know how CPU are internally structured how different CPUs differ from each other ,and how CPU speed is evaluated. These and other related concepts about CPU are described below.

The Control Unit.

We saw that the two basic components of a CPU are the control unit and the arithmetic logic unit. The control unit of the CPU selects and interprets program instructions, and then sees that they are executed. It has some special purpose registers (whose functions are described in a latter subsection), and a decoder to perform these activities. The special purpose registers, namely the Instructions register and the program control register, respectively hold the current instruction and the next instruction to be executed, and in this way help the control unit in instruction selection. On the other hand. The decoder has the necessary circuitry to decode and interpret the meaning of every instruction supported by the CPU. Each instruction is accompanied by microcode—very basic directions. Which tell the CPU how to execute the instruction?
Although, the control unit does not perform any actual processing of the data, it acts as a central nervous system for other components of the computer. It manages and coordinates the entire computer system, including the input and output units. It obtains instructions from the program stored in the main memory, interprets the instructions, and issues signal, which cause other units of the system to execute them.

The Arithmetic Logic Unit (ALU)

The ALU of the CPU is the place, where the actual execution of the instructions takes place, during the data procession operation. That is, when the control unit encounters an instruction, which involves an arithmetic operation (such as, add, subtract, multiply, divide), or a logic operation (such as less than, equal to, greater that), it passes control to the ALU. The ALU has some special purpose registers and the necessary circuitry, to carry out all the arithmetic and logic operations, which are included in the instructions supported by the CPU. For example, the arithmetic and logic operations, which are included in the instructions supported by the CPU.For example, the control unit might load two numbers into the registers in the ALU.Then, it might the ALU to add the two numbers (an arithmetic operations), or to check if the two numbers are equal (a logical operation).

In case of a microcomputer, the entire CPU (both the control unit and the ALU) is contained on a single tiny silicon chip, called a microprocessor.