The computer system hardware
CPU (Central Processing Unit):
CPU or central processing unit is an electronic circuitry that carries out the instruction given by a computer program. CPU execute instruction by performing basic arithmetic, logical, control and I/O operations as required per instruction. CPU is considered to be the brain of the computer. The speed and efficiency of a computer mostly depends that of it's CPU. It is both the combination of control unit(CU) and ALU. It is also known as heart of computer.�� Functions of CPU
Among various functions of CPU some are as follows�Controlling all other parts of the machine and sending timing signals. Transferring data between memory and I/O devices Fetching data and instructions from memory Decoding instruction Performing arithmetical and logical operations Executing programs stored in memory Performing communication among the I/O devices etc.
Memory units
Primary storage, or memory, means the space on your hard drive that is briefly used for working space. This usually occurs in a chip. Memory consists of four types of memory chips RAM, ROM, CMOS and flash. RAM stand for random access memory and ROM stand for read only memory. These are also called primary memory of a computer. Memory units is the data storage location of computer where stores data permanently or temporarily. As for example RAM ,ROM, magnetic tape, magnetic disk(floppy disk ,hard disk) ,pen drive etc
Memory unit is two types
Main or primary memory
Auxiliary or secondary memory
Main or primary memory:
Stores data permanently or temporarily. As for example RAM & ROM , cache memory ,register etc.
Instruction Format
An instruction is normally made up of a combination of an operation code and some way of specifying an operand, most commonly by its location or address in memory though nonmemory reference instructions can exist. Some operation codes deal with more than one operand; the locations of these operands may be specified using any of the many addressing schemes.
Classically, the number of address references has been used to specify something about the architecture of a particular computer. In some instruction formats and machine architectures, the number of operand references may be fixed; in others the number is variable. In the former case descriptions of formats include one-address, two-address, three-address, and (now rarely) four-address. An example (symbolically) of a one-address instruction is.
Example
add x i.e.
�add contents of address x
�to contents of accumulator;
�sum remains in accumulator.
�An example of a three-address instruction is
�add x,y,z i.e.
�add contents of address x
�to contents of address y;
�sum is placed in location z.
Instruction Set
An instruction set architecture (ISA) is an abstract model of a computer. It is also referred to as architecture or computer architecture. A realization of an ISA is called an implementation. An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware. Software that has been written for an ISA can run on different implementations of the same ISA.
This has enabled binary compatibility between different generations of computers to be easily achieved, and the development of computer families. Both of these developments have helped to lower the cost of computers and to increase their applicability. For these reasons, the ISA is one of the most important abstractions in computing today.
Instruction Cycle
The instruction cycle (also known as the fetch–decode–execute cycle or the fetch-execute cycle) is the basic operational process of a computer system. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction describes, and then carries out those actions. This cycle is repeated continuously by a computer's central processing unit (CPU), from boot-up until the computer has shut down.
A diagram of the instruction cycle.
In simpler CPUs the instruction cycle is executed sequentially, each instruction being processed before the next one is started. In most modern CPUs the instruction cycles are instead executed concurrently, and often in parallel, through an instruction pipeline: the next instruction starts being processed before the previous instruction has finished, which is possible because the cycle is broken up into separate steps.
Microprocessor
A microprocessor is an integrated circuit (IC) which incorporates core functions of a computer’s central processing unit (CPU). It is a programmable multipurpose silicon chip, clock driven, register based, accepts binary data as input and provides output after processing it as per the instructions stored in the memory.
�How does a Microprocessor work ?�
A processor is the brain of a computer which basically consists of Arithmetical and Logical Unit (ALU), Control Unit and Register Array. As the name indicates ALU performs all arithmetic and logical operations on the data received from input devices or memory. Register array consists of a series of registers like accumulator (A), B, C, D etc. which acts as temporary fast access memory locations for processing data. As the name indicates, control unit controls the flow of instructions and data throughout the system.
So, basically a microprocessor takes input from input devices, process it as per instructions given in the memory and produces output.
Advantages of a Microprocessor�
Low Cost�
Microprocessors are available at low cost due to integrated circuit technology. Which will reduce the cost of a computer system.
High Speed�
Microprocessor chips can work at very high speed due to the technology involved in it. It is capable of executing millions of instructions per second.
Small Size�
Due to very large scale and ultra large scale integration technology, a microprocessor is fabricated in a very less footprint. This will reduce the size of the entire computer system.
contd
Versatile�
Microprocessors are very versatile, the same chip can be used for a number of applications by simply changing the program (instructions stored in the memory).
Low Power Consumption
�Microprocessors are usually manufactured using metal oxide semiconductor technology, in which MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are working in saturation and cut off modes. So the power consumption is very low compared to others.
Less Heat Generation�Compared to vacuum tube devices, semiconductor devices won’t emit that much heat.
Reliable�Microprocessors are very reliable, failure rate is very less as semiconductor technology is used.
Portable�Devices or computer system made with microprocessors can be made portable due to the small size and low power consumption.
Interconnecting the units of a computer
Modern computer systems have a recursive structure of processing and storage elements that are interconnected to make larger elements: Functional units connected to registers and on-chip cache. Multiple processors and caches connected to main memories. Computing nodes connected by a message-passing local area network. Local area networks bridged to form an extended LAN. Networks connected in a wide-area internet. All the computers in the world exchanging electronic mail.
Inside a computer cabinet
Processor
Motherboard
Hard drive
Power supply
Computer Architecture
The design & organization parts of a computer system is called computer Architecture. RISC & CISC is the technologies on which design & architecture of microprocessor is based.
RISC
RISC means reduced instruction set computer in which each instruction has dedicated electronic circuits made from gates, to generate control signal. As for example Power PC,ULTRASPARC etc.
Characteristics Simple instruction set.
Same length instructions.
1-machine –cycle instructions.
Advantages of Risc
Speed : 2 to 4 times the performance.
Simpler hardware.
Shorter design cycle : They can be design more quickly.
CISC
CISC means complex instruction set computer which based on microprogramming techniques.
The hardware is controlled by instructions coded in control memory. Such instruction is called microinstruction & coding process is called microprogramming.Cisc is more complex but efficient processor designing technique. As for example Intel 80386,80486,80586,pentiumI,II,III,IV,Celeron,I3,I5,I7 etc.
Advantages of CISC
Microprogramming is easy as assembly language to implement & much expensive than hardwiring a control unit.
Micro coding instructions allowed to the designers to make CISC machine upwardly compatible.
As each instruction become more capable, fewer instructions could be used to implement a given task.
Disadvantages
Earlier generations of a processor family were generally contained as a subset in every new versions so instruction set & each generations of computers.
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