Main Memory

Computer's CPU contains necessary circuitry for data processing and controlling other components of the computer. However, one thing it does not have built into it the to store programs and data needed during data processing. The CPU contains several registers for storing data and instructions but they can store only a few bytes at a time. They are just sufficient to hold one two instructions with corresponding data. If instructions and data of an executing program were to reside in secondary storage like a disk, and fetched and loaded one by one into CPU registers as the program execution proceeded, this would load the CPU being idle most of the time. This is because there is a large speed mismatch between the rate at which CPU can process data and the rate at which the system can transfer data from disk to CPU registers.

For example, a CPU can process data at a rate of above 5 nanoseconds/byte and a disk reader can read data at a speed of about 5 microseconds/byte. Hence, within the time in which a disk can supply one byte of data a CPU can process 1000 bytes. This would lead to very poor overall performance even for a computer having a very fast CPU. To overcome this problem there is a need to have a reasonable large storage space that can hold instructions and the data of the program (s) on which CPU is currently working. The time to fetch and load data from this storage space into CPU registers must also be very small as compared to that form disk storage to reduce the speed mismatch problem with CPU speed. Every computer has such a storage space known as primary storage, main memory or simply memory.

Instructions and the data of the program reside mainly in this area when CPU is executing the program. Physically, this memory consist of some integrated circuit chips either on the motherboard or on a small circuit board attached to the motherboard of computer system. This built-in memory allows CPU restore and retrieve data very quickly. The rate of fetching data from this memory is the order of 50 nanoseconds per byte. Hence, the rate of data fetching from main memory is about 100 times faster than that form a high speed secondary storage like disk.

Storage Evolution Criteria :

Any storage unit of a computer system is characterized and evoluted based on following properties:

1. Storage capacity:

It the amount of data, which is storage unit can store. Larger storage capacity is desirable. As compared to secondary storage units, primary storage units have less storage capacity.

2. Access time:

It is the time required to locate and retrieve stored data from the storage unit in response to a program instruction. Faster access time is preferable. As compared to secondary storage units, primary storage units have faster access time.

3. Cost per bit of storage:

It refers to the cost of a storage unit for a given storage capacity. Lower cost is desirable. As compared to secondary storage units, primary storage units have higher cost per bit of storage.

4. Volatile:

If a storage unit can retain data stored in it even in case of power off or interruption of power, it is called non volatile storage. On the other hand, if a storage unit loses data stored in it in case of power off or interruption of power, it is called volatile storage. Obviously, non volatile storage is desirable. In almost all computer systems, primary storage units are volatile and secondary storage units are non volatile.

5. Random access:

If the time taken to access a peace of data from a storage unit is independent of the location of the data in the storage unit, it is called random access storage or random access memory (RAM). Each location of a RAM is as easy to access as any other locations and takes the same amount of time. In almost all computer systems primary storage units have random access property and secondary storage units have either pseudo random access ( access time is nearly same for all locations but not exactly same) or sequential access ( access time depends on the location of the data) property.

Comments

Word-processing Package

The term word processing describes use of hardware and software to create, edit, view, format, store, retrieve and print documents (written materials such as letters, reports, books, etc.). A word processing package enables us to do all these on computer system. Commonly supported features: Today's word processing packages normally support the features described below: 1. Entering Text : This feature allows a user to enter text with computer's keyboard. Every character typed on keyboard is displayed immediately on computer's screen. Word wrap feature of word processing software determines when current line is full, and it automatically moves the text that follows to the next line. Hence, only time the user has to press Enter key is at the end of the paragraph. This feature is very useful to those having fast typing speed because they can enter text at their speed, without the need to keep track of where to end a line. 2. Editing Text : This feature allows a user to make cha

Computer Languages - introduction

This chapter continues with the discussion of development of computer programs. Once a programmer has finished planning of a computer program, he/she is now ready to write the steps of the corresponding algorithm in a programming language. Computer language or programming language is a language acceptable to a computer system, and the process of writing instructions in such a language is called programming or coding. The goal of this post is to introduce some popular programming languages. Analogy with natural languages: Language is a mans of communication. We use a natural language such as English, to communicate our emotions and ideas to others. Similarly a programmer uses a computer language to instruct computer what he/she want to do. All natural languages (English, French, German, etc.) use a standard set of words and symbols for communication. Everyone uses that language understands these words and symbols. The set of words allowed in a language is called its vocabulary.

Central Processing Unit

Central Processing Unit (CPU) A Central Processing Unit is also called a processor, central processor, or microprocessor. It carries out all the important functions of a computer. It receives instructions from both the hardware and active software and produces output accordingly. It stores all important programs like operating systems and application software. CPU also helps Input and output devices to communicate with each other. Owing to these features of CPU, it is often referred to as the brain of the computer. Central Processing Unit CPU is installed or inserted into a CPU socket located on the motherboard. Furthermore, it is provided with a heat sink to absorb and dissipate heat to keep the CPU cool and functioning smoothly. Generally, a CPU has three components: 1. Control Unit 2. Arithmetic Logic Unit 3. Memory or Storage Unit 1. Control Unit : It is the circuitry in the control unit, which makes use of electrical signals to instruct the computer system for executing already

Introduction to Computer

The word "computer" comes from the word "compute", which means "to calculate". Hence, people usually consider a computer to be a calculating device that can perform arithmetic operations at high speed. The straightforward meaning of a computer is a machine that can calculate. However, modern computers are not just a calculating device anymore. They can perform a variety of tasks. In simple terms, a computer is a programmable electronic machine used to store, retrieve, and process data. According to the definition, " A computer is a programmable electronic device that takes data, perform instructed arithmetic and logical operations, and gives the output." Whatever is given to the computer as input is called 'data', while the output received after processing is called 'information'. Although the original objective of inventing a computer was to create a fast calculating device, we name define a computer as a device that operates

Computer system architecture

Computer Architecture A computer system is basically a machine that simplifies complicated tasks. It should maximize performance and reduce costs as well as power consumption.The different components in the Computer System Architecture are Input Unit, Output Unit, Storage Unit, Arithmetic Logic Unit, Control Unit etc. A diagram that shows the flow of data between these units is as follows − The input data travels from input unit to ALU. Similarly, the computed data travels from ALU to output unit. The data constantly moves from storage unit to ALU and back again. This is because stored data is computed on before being stored again. The control unit controls all the other units as well as their data. Details about all the computer units are − Input Unit The input unit provides data to the computer system from the outside. So, basically it links the external environment with the computer. It takes data from the input devices, converts it into machine language and then loads it into t

COMPUTER BASICS

Search This Blog