computer evolution

UNIT 1 Basics of Computer and its Evolution

By: Nitin Nagpal 1

Introduction of Computer

The term computer is derived from the word compute, which means to calculate.

In its most basic form a computer is any device which aids humans in performing various kinds of computations or calculations. In that respect the earliest computer was the abacus, used to perform basic arithmetic operations.

The first electronic digital computers were developed between 1940 and 1945. Originally they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).In this era mechanical analog computers were used for military applications.

Every computer supports some form of input, processing, and output. This is less obvious on a primitive device such as the abacus where input, output and processing are simply the act of moving the pebbles into new positions, seeing the changed positions, and counting. Regardless, this is what computing is all about, in a nutshell. We input information; the computer processes it according to its basic logic or the program currently running, and outputs the results.

Modern computers do this electronically, which enables them to perform a vastly greater number of calculations or computations in less time. Despite the fact that we currently use computers to process images, sound, text and other non-numerical forms of data, all of it depends on nothing more than basic numerical calculations. Graphics, sound etc. are merely abstractions of the numbers being crunched within the machine; in digital computers these are the ones and zeros, representing electrical on and off states, and endless combinations of those. In other words every image, every sound, and every word have a corresponding binary code.

What is computer?

A computer is a programmable machine that receives

input, stores and manipulates data/information, and

provides output in a useful format.

or

A computer is an electronic device that manipulates

information or "data." It has the ability to store,

retrieve, and process data. You can use a computer to

type documents, send email, and surf the Internet.

You can also use it to handle spreadsheets,

accounting, database management, presentations,

games, and more.

http://en.wikipedia.org/wiki/Digital_data

http://en.wikipedia.org/wiki/Personal_computer

http://en.wikipedia.org/wiki/Mechanical_computer

http://en.wikipedia.org/wiki/Analog_computers



http://en.wikipedia.org/wiki/Machine

http://en.wikipedia.org/wiki/Data_(computing)

http://en.wikipedia.org/wiki/Information


By: Nitin Nagpal 2

Evaluation of Computers The origin of computer technology took place in the 19th century. People desired to have a machine that would carry out mathematical calculations for them. The ABACUS is considered to have been the first computer in the world. It was used to perform simple measurements and calculations. The abacus (plural abaci or abacuses), also called a counting frame, is a calculating tool used primarily in parts of Asia for performing arithmetic processes.

ABACUS is available even today for school going children. In the 17th century, a scientist named Pascal developed a machine that could perform mathematical calculations. This machine comprised of a number of gears. The movement of gear mechanism was used to perform some calculations. He named the machine PASCALINE. However, the concept of the modern computer was propounded by the scientist and mathematician Charles Babbage. He first wrote on the use of logic and loops in process execution. Based on the concept of logic and loops, Babbage envisaged two models for performing computations- Analytical Engine and Difference Engine. In those days, electronics was not developed. Therefore, these models proposed by Babbage existed only on paper. However, the ideas given by Babbage were implemented after the invention of electronics.

George Boolean developed the famous Boolean Algebra based on binary numbers.

De Morgan put forward theorems on logic gates. These theorems are known as De Morgan’s

Theorems.

Lady Ada was the first computer programmer.

The real application of computers began in the late fifties. The computers were used in the United States for various applications such as census, defence, R&D, universities etc.

http://en.wikipedia.org/wiki/Arithmetic


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Generation of Computer

First Generation Computers (1940s – 1950s)

First electronic computers used vacuum tubes, and they were huge and complex. The first general purpose electronic computer was the ENIAC (Electronic Numerical

Integrator And Computer). It was digital, although it didn’t operate with binary code, and was reprogrammable to

solve a complete range of computing problems. It was programmed using plug boards and switches, supporting

input from an IBM card reader, and output to an IBM card punch. It took up 167 square meters, weighed 27 tons, and

consuming 150 kilowatts of power. It used thousands of vacuum tubes, crystal diodes, relays, resistors, and

capacitors.

The first non-general purpose computer was ABC (Atanasoff–Berry Computer), and other similar computers of this era included german Z3, ten British Colossus computers, LEO, Harvard

Mark I, and UNIVAC.

Second Generation Computers (1955 – 1960)

The second generation of computers came about thanks

to the invention of the transistor, which then started replacing vacuum tubes in computer design. Transistor

computers consumed far less power, produced far less heat, and were much smaller compared to the first

generation, albeit still big by today’s standards.

The first transistor computer was created at the

University of Manchester in 1953. The most popular of transistor computers was IBM 1401. IBM also created the

first disk drive in 1956, the IBM 350 RAMAC.

Third Generation Computers (1960s)

The invention of the integrated circuits (ICs), also known as microchips, paved the way for computers as we know them

today. Making circuits out of single pieces of silicon, which is a semiconductor, allowed them to be much smaller and

more practical to produce. This also started the ongoing process of integrating an ever larger number of transistors


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onto a single microchip. During the sixties microchips started making their way into computers,

but the process was gradual, and second generation of computers still held on.

First appeared minicomputers, first of which were still based on non-microchip transistors, and later versions of which were hybrids, being based on both transistors and microchips, such as

IBM’s System/360. They were much smaller, and cheaper than first and second generation of computers, also known as mainframes. Minicomputers can be seen as a bridge between

mainframes and microcomputers, which came later as the proliferation of microchips in computers grew.

Fourth Generation Computers (1971 – present)

First microchips-based central processing units consisted of multiple microchips for different

CPU components. The drive for ever greater integration and miniaturization led towards single-chip CPUs, where all of the necessary CPU components were put onto a single microchip, called

a microprocessor. The first single-chip CPU, or a microprocessor, was Intel 4004.

The advent of the microprocessor spawned the evolution of the microcomputers, the kind that

would eventually become personal computers that we are familiar with today.

ADVANTAGES OF COMPUTERS Compared to traditional systems, computers offer many noteworthy advantages. This is one reason that traditional systems are being replaced rapidly by computer-based systems. The main advantages offered by computers are as follows: • High Accuracy • Superior Speed of Operation • Large Storage Capacity • User-friendly Features • Portability • Platform independence • Economical in the long term


By: Nitin Nagpal 5

Classification of computers

Analog Computers and Digital computers are the two kinds of computers, the combination of which is responsible for the invention of the modern Hybrid computers.

Working on binary mathematics.

Examples of digital computers are personal computers, supercomputers, mainframe computers etc.

Supercomputers Are the most powerful computers in terms of speed of execution and large storage capacity. NASA uses supercomputers to track and control space explorations.

Mainframe Computers Are next to supercomputers in terms of capacity. The mainframe computers are multi terminal computers, which can be shared simultaneously by multiple users. Unlike personal computers, mainframe computers offer time-sharing

For example, insurance companies use mainframe computers to process information about millions of its policyholders.


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Minicomputers These computers are also known as midrange computers. These are desk-sized machines and are used in medium scale applications. For example, production departments use minicomputers to monitor various manufacturing processes and assembly-line operations.

Microcomputers As compared to supercomputers, mainframes and minicomputers, microcomputers are the least powerful, but these are very widely used and rapidly gaining in popularity.

Personal Computer PC is the term referred to the computer that is designed for use by a single person. PCs are also called microcontrollers because these are smaller when compared to mainframes and minicomputers. The term ‘PC’ is frequently used to refer to desktop computers. Although PCs are used by individuals, they can also be used in computer networks.

BASIC COMPUTER OPERATIONS (Block diagram or Architecture of Computer System)

A computer as shown in Fig. performs basically five major operations or functions irrespective of

their size and make. These are 1) it accepts data or instructions by way of input, 2) it stores

data, 3) it can process data as required by the user, 4) it gives results in the form of output, and

5) it controls all operations inside a computer. We discuss below each of these operations.

1. Input: This is the process of entering data and programs in to the computer system. You

should know that computer is an electronic machine like any other machine which takes as

inputs raw data and performs some processing giving out processed data. Therefore, the input

unit takes data from us to the computer in an organized manner for processing.

Fig:Basic computer Operations

2. Storage: The process of saving data and instructions permanently is known as storage. Data

has to be fed into the system before the actual processing starts. It is because the processing


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speed of Central Processing Unit (CPU) is so fast that the data has to be provided to CPU with

the same speed. Therefore the data is first stored in the storage unit for faster access and

processing. This storage unit or the primary storage of the computer system is designed to do

the above functionality. It provides space for storing data and instructions.

The storage unit performs the following major functions:

All data and instructions are stored here before and after processing.

Intermediate results of processing are also stored here.

3. Processing: The task of performing operations like arithmetic and logical operations is called

processing. The Central Processing Unit (CPU) takes data and instructions from the storage

unit and makes all sorts of calculations based on the instructions given and the type of data

provided. It is then sent back to the storage unit.

4. Output: This is the process of producing results from the data for getting useful information.

Similarly the output produced by the computer after processing must also be kept somewhere

inside the computer before being given to you in human readable form. Again the output is also

stored inside the computer for further processing.

5. Control: The manner how instructions are executed and the above operations are

performed. Controlling of all operations like input, processing and output are performed by

control unit. It takes care of step by step processing of all operations in side the computer.

FUNCTIONAL UNITS

In order to carry out the operations mentioned in the previous section the computer allocates the

task between its various functional units. The computer system is divided into three separate

units for its operation. They are 1) arithmetic logical unit, 2) control unit, and 3) central

processing unit.

1. Arithmetic Logical Unit (ALU)

After you enter data through the input device it is stored in the primary storage unit. The actual

processing of the data and instruction are performed by Arithmetic Logical Unit. The major

operations performed by the ALU are addition, subtraction, multiplication, division, logic and

comparison. Data is transferred to ALU from storage unit when required. After processing the

output is returned back to storage unit for further processing or getting stored.

2. Control Unit (CU)

The next component of computer is the Control Unit, which acts like the supervisor seeing that

things are done in proper fashion. The control unit determines the sequence in which computer

programs and instructions are executed. Things like processing of programs stored in the main

memory, interpretation of the instructions and issuing of signals for other units of the computer


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to execute them. It also acts as a switch board operator when several users access the

computer simultaneously. Thereby it coordinates the activities of computer’s peripheral

equipment as they perform the input and output. Therefore it is the manager of all operations

mentioned in the previous section.

3. Central Processing Unit (CPU)

The ALU and the CU of a computer system are jointly known as the central processing unit. You

may call CPU as the brain of any computer system. It is just like brain that takes all major

decisions, makes all sorts of calculations and directs different parts of the computer functions by

activating and controlling the operations.

What is Hardware?

Computer system hardware includes the CPU and its associated input and output devices. Input and output devices, separate from the CPU itself, are called peripheral equipment. The CPU communicates with each peripheral device through input and output channels. To operate an electronic-imaging workstation, you must have a general understanding of CPU primary and secondary storage, peripheral devices, input and output

channels, and modems.


By: Nitin Nagpal 9

Input and Output Devices

The computer will be of no use unless it is able to communicate with the outside world.

Input/Output devices are required for users to communicate with the computer.

In simple terms, input devices bring information INTO the computer and output devices bring

information OUT of a computer system. These input/output devices are also known as

peripherals since they surround the CPU and memory of a computer system. Some commonly

used Input/Output devices are listed in table below.

Input Devices Output Devices

Keyboard Monitor

Mouse LCD

Joystick Printer

Scanner Plotter

Light Pen

Touch Screen

Input Devices

(a) Keyboard

It is a text base input device that allows the user to input alphabets, numbers and Other

characters. It consists of a set of keys mounted on a board.


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Alphanumeric Keypad It consists of keys for English alphabets, 0 to 9 numbers, and special characters like +−/ * (

) etc.

Function Keys

There are twelve function keys labeled F1, F2, F3… F12. The functions assigned to these

keys differ from one software package to another. These keys are also user programmable

keys.

Special-function Keys These keys have special functions assigned to them and can be used only for those specific

purposes. Functions of some of the important keys are defined below.

Enter

It is similar to the ‘return’ key of the typewriter and is used to execute a command or

program.

Spacebar

It is used to enter a space at the current cursor location.

Backspace

This key is used to move the cursor one position to the left and also delete the character in

that position.

Delete

It is used to delete the character at the cursor position.

Insert

Insert key is used to toggle between insert and overwrite mode during data entry.

Shift

This key is used to type capital letters when pressed along with an alphabet key. Also used

to type the special characters located on the upper-side of a key that has two characters

defined on the same key.

Caps Lock

Cap Lock is used to toggle between the capital lock features. When ‘on’, it locks the

alphanumeric keypad for capital letters input only.

Tab

Tab is used to move the cursor to the next tab position defined in the document. Also, it is

used to insert indentation into a document.

Ctrl Control key is used in conjunction with other keys to provide additional functionality on the

keyboard.


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Alt Also like the control key, Alt key is always used in combination with other keys to perform

specific tasks.

Esc

This key is usually used to negate a command. Also used to cancel or abort executing

programs.

Numeric Keypad

Numeric keypad is located on the right side of the keyboard and consists of keys having

numbers (0 to 9) and mathematical operators (+ −* /) defined on them. This keypad is

provided to support quick entry for numeric data.

Cursor Movement Keys

These are arrow keys and are used to move the cursor in the direction indicated by the

arrow (up, down, left, right).

(b) Mouse

The mouse is a small device used to point to a particular place on the screen and select in order

to perform one or more actions. It can be used to select menu commands, size windows, start

programs etc. The most conventional kind of mouse has two buttons on top: the left one being

used most frequently.

Mouse Actions

Left Click : Used to select an item.

Double Click : Used to start a program or open a file.

Right Click : Usually used to display a set of commands.

Drag and Drop : It allows you to select and move an item from one location to

another. To achieve this place the cursor over an item on the screen, click

the left mouse button and while holding the button down move the cursor

to where you want to place the item, and then release it.


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(c) Joystick

The joystick is a vertical stick which moves the graphic cursor in a direction the stick is moved. It

typically has a button on top that is used to select the option pointed by the cursor. Joystick is

used as an input device primarily used with video games, training simulators and controlling

robots

(d)Scanner

Scanner is an input device used for direct data entry from the source document into the

computer system. It converts the document image into digital form so that it can be fed into the

computer. Capturing information like this reduces the possibility of errors typically experienced

during large data entry.

Hand-held scanners are commonly seen in big stores to scan codes and price information for

each of the items. They are also termed the bar code readers.

(e) Bar codes

A bar code is a set of lines of different thicknesses that represent a number. Bar Code Readers

are used to input data from bar codes. Most products in shops have bar codes on them.Bar

code readers work by shining a beam of light on the lines that make up the bar code and

detecting the amount of light that is reflected back.

(f) Light Pen

It is a pen shaped device used to select objects on a display screen. It is quite like the mouse (in

its functionality) but uses a light pen to move the pointer and select any object on the screen by

pointing to the object.

Users of Computer Aided Design (CAD) applications commonly use the light pens to directly

draw on screen.

(g) Touch Screen

It allows the user to operate/make selections by simply touching the display screen. Common

examples of touch screen include information kiosks, and bank ATMs.

(h)Digital camera

A digital camera can store many more pictures than an ordinary camera. Pictures taken using a

digital camera are stored inside its memory and can be transferred to a computer by connecting

the camera to it. A digital camera takes pictures by


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converting the light passing through the lens at the front into a digital image.

Output Devices

(a) Monitor

Monitor is an output device that resembles the television screen and uses a Cathode Ray Tube

(CRT) to display information. The monitor is associated with a keyboard for manual input of

characters and displays the information as it is keyed in. It also displays the program or

application output. Like the television, monitors are also available in different sizes.

(b) Liquid Crystal Display (LCD)

LCD was introduced in the 1970s and is now applied to display terminals also. Its advantages

like low energy consumption, smaller and lighter have paved its way for usage in portable

computers (laptops).

(c) Printer

Printers are used to produce paper (commonly known as hardcopy) output. Based on the

technology used, they can be classified as Impact or Non-impact printers.

(d) Audio Output: Sound Cards and Speakers:

The Audio output is the ability of the computer to output sound. Two components are needed:

Sound card – Plays contents of digitized recordings, Speakers – Attached to sound card.


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Figure 2

Personal Computer Configuration

Now let us identify the physical components that make the computer work. These are

1. Central Processing Unit (CPU)

2. Computer Memory (RAM and ROM)

3. Data bus

4. Ports

5. Motherboard

6. Hard disk

7. Output Devices

8. Input Devices

All these components are inter-connected for the personal computer to work.


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MEMORY SYSTEM IN A COMPUTER

A memory is just like a human brain. It is used to store data and instruction. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts. Each part is called cell. Each location or cell has a unique address which varies from zero to memory size minus one.

For example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory location. The address of these locations varies from 0 to 65535.

Memory is primarily of two types

Internal Memory - cache memory and primary/main memory External Memory - magnetic disk / optical disk etc.

Characteristics of Memory Hierarchy are following when we go from top to bottom.

Capacity in terms of storage increases.

Cost per bit of storage decreases.

Frequency of access of the memory by the CPU decreases.

Access time by the CPU increases

In other terms……

There are two kinds of computer memory: primary and secondary. Primary memory is

accessible directly by the processing unit. RAM is an example of primary memory. As soon as

the computer is switched off the contents of the primary memory is lost. You can store and

retrieve data much faster with primary memory compared to secondary memory. Secondary

memory such as floppy disks, magnetic disk, etc., is located outside the computer. Primary

memory is more expensive than secondary memory. Because of this the size of primary

memory is less than that of secondary memory. We will discuss about secondary memory later

on.

Computer memory is used to store two things:

i) Instructions to execute a program and ii) Data. When the computer is doing any job, the data that have to be processed are

stored in the primary memory. This data may come from an input device like

keyboard or from a secondary storage device like a floppy disk.


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REGISTERS

The CPU processes data and instructions with high speed, there is also movement of data between various units of computer. It is necessary to transfer the processed data with high speed. So the computer uses a number of special memory units called registers. They are not

part of the main memory but they store data or information temporarily and pass it on as

directed by the control unit.

RAM

A RAM constitutes the internal memory of the CPU for storing data, program and program result. It is read/write memory. It is called random access memory (RAM).

Since access time in RAM is independent of the address to the word that is, each storage location inside the memory is as easy to reach as other location & takes the same amount of time. We can reach into the memory at random & extremely fast but can also be quite expensive.

RAM is volatile, i.e. data stored in it is lost when we switch off the computer or if there is a power failure. Hence a backup uninterruptible power system(UPS) is often used with computers. RAM is small , both in terms of its physical size and in the amount of data it can hold.


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RAM is of two types

Static RAM (SRAM)

Dynamic RAM (DRAM)

STATIC RAM (SRAM) The word static indicates that the memory retains its contents as long as power remains applied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.

Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher.

Static RAM is used as cache memory needs to be very fast and small.

DYNAMIC RAM (DRAM) DRAM, unlike SRAM, must be continually refreshed in order for it to maintain the data. This is

done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells. These cells are composed of one capacitor and one transistor.

ROM

ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture.

A ROM, stores such instruction as are required to start computer when electricity is first turned on, this operation is referred to as bootstrap. ROM chip are not only used in the computer but also in other electronic items like washing machine and microwave oven.

Following are the various types of ROM

MROM (MASKED ROM)

The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs. It is inexpensive ROM.

PROM (PROGRAMMABLE READ ONLY MEMORY)

PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM programmer. Inside the PROM chip there are small fuses which are burnt open during programming. It can be programmed only once and is not erasable.


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EPROM(ERASABLE AND PROGRAMMABLE READ ONLY MEMORY)

The EPROM can be erased by exposing it to ultra-violet light for a duration of upto 40 minutes. Usually, a EPROM eraser achieves this function. During programming an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.

EEPROM(ELECTRICALLY ERASABLE AND PROGRAMMABLE READ

ONLY MEMORY)

The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 ms (milli second). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of re-programming is flexible but slow.

Serial Access Memory

Sequential access means the system must search the storage device from the beginning of the memory address until it finds the required piece of data. Memory device which supports such access is called a Sequential Access Memory or Serial Access Memory. Magnetic tape is an example of serial access memory.

Direct Access Memory

Direct access memory or Random Access Memory, refers to condition in which a system can go directly to the information that the user wants. Memory device which supports such access is called a Direct Access Memory. Magnetic disk, optical disks are an examples of direct access memory.

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory. It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.

ADVANTAGES

Cache memory is faster than main memory.

It consumes less access time as compared to main memory.

It stores the program that can be executed within a short period of time.

It stores data for temporary use.


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DISADVANTAGES

Cache memory has limited capacity.

It is very expensive.

Virtual memory is a technique that allows the execution of processes which are not completely available in memory. The main visible advantage of this scheme is that programs can be larger than physical memory. Virtual memory is the separation of user logical memory from physical memory.

This separation allows an extremely large virtual memory to be provided for programmers when only a smaller physical memory is available. Following are the situations, when entire program is not required to be loaded fully in main memory.

User written error handling routines are used only when an error occured in the data or computation.

Certain options and features of a program may be used rarely.

Many tables are assigned a fixed amount of address space even though only a small amount of the table is actually used.

The ability to execute a program that is only partially in memory would counter many benefits.

Less number of I/O would be needed to load or swap each user program into memory.

A program would no longer be constrained by the amount of physical memory that is available.

Each user program could take less physical memory, more programs could be run the same time, with a corresponding increase in CPU utilization and throughput.

Auxiliary Memory/Secondary

Auxiliary memory is much larger in size than main memory but is slower. It normally stores system programs, instruction and data files. It is also known as secondary memory. It can also be used as an overflow/virtual memory in case the main memory capacity has been exceeded. Secondary memories can not be accessed directly by a processor. First the data / information of auxillary memory is transferred to the main memory and then that information can be accessed by the CPU. Characteristics of Auxiliary Memory are following

Non-volatile memory - Data is not lost when power is cut off. Reusable - The data stays in the secondary storage on permanent basis until it is not

overwritten or deleted by the user. Reliable - Data in secondary storage is safe because of high physical stability of secondary

storage device. Convenience - With the help of a computer software, authorized people can locate and access

the data quickly. Capacity - Secondary storage can store large volumes of data in sets of multiple disks. Cost - It is much lesser expensive to store data on a tape or disk than primary memory.


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Difference Between Primary and Secondary Memory

Primary memory vs Secondary memory Processor access the primary memory in a random fashion. Unlike primary memory, secondary memory is not directly accessed through CPU. The accessing of the primary memory through CPU is done by making use of address and data buses, whereas input/ output channels are used to access the secondary memory.

The primary memory is embedded with two types of memory technologies; they are the RAM (Random Access Memory) and ROM (Read Only Memory). The secondary memory is accessible in the form of Mass storage devices such as hard disk, memory chips, Pen drive, floppy disk storage media, CD and DVD.

Primary memory is volatile in nature, while secondary memory is non volatile. The information that is stored in the primary memory cannot be retained when the power is turned off. In case of secondary memory, the information can be retrieved even if the power is turned off because the data will not be destructed until and unless the user erases it.

When the data processing speed is compared between the primary and secondary memory, the primary memory is much faster than the secondary memory.

In the cost perspective, the primary memory is costlier than the secondary memory devices. Because of this reasons most of the computer users install smaller primary memory and larger secondary memory.

As the secondary memory is permanent, all the files and programs are stored in the secondary memory most and as the primary memory interacts very fast with the micro processor, when the computer needs to access the files that are stored in the secondary memory, then such files are first loaded into the primary memory and then accessed by the computer. More……..

Primary Memory Secondary Memory

These are semiconductor memories. These are magnetic and optical memories.

They are characterized as volatile random

access memories (RAM) or non-volatile

memories (ROM). They are non-volatile.

They contain program and data that is

currently being used by micro processor. These are used to for bulk storage.

These memories are fast enough to interact

with the microprocessor. Slower than primary memories.

Also known as Main Memory

Also known as Backup Memory or Auxiliary

Memory. E.g. Tapes, Floppies, Hard Discs, CD

ROMs, DVDs

http://verticalhorizons.in/difference-between-primary-and-secondary-memory/verticalhorizons.in/difference-between-ram-and-rom/

http://verticalhorizons.in/difference-between-volatile-memory-and-non-volatile-memory/


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Capacity of Primary Memory

You know that each cell of memory contains one character or 1 byte of data. So the capacity is

defined in terms of byte or words. Thus 64 kilobyte (KB) memory is capable of storing 64 * 1024

= 32,768 bytes. (1 kilobyte is 1024 bytes).

1 byte= 8 bits

1KB=1024 byte

1MB=1024 KB (MB stands for Mega Byte)

ITB=1024MB (TB stands for Tera Byte)

A memory size ranges from few kilobytes in small systems to several thousand kilobytes in

large mainframe and super computer. In your personal computer you will find memory capacity

in the range of 64 KB, 4 MB, 8 MB and even 16 MB (MB = Million bytes).

The following table highlights the major difference between the RAM memory and ROM

memory:

Options RAM ROM

Elaboration Random Access Memory Read Only memory

Accessibility In reference with the processor, the

information stored in the RAM is

easily accessed

The processor cannot directly access the

information that is stored in the ROM. In

order to access the ROM information, first the

information will be transferred into the RAM

and then it gets executed by the processor

Working type Both the read and write operations

can be performed over the

information that is stored in the

RAM

The ROM memory only allows the user to

read the information. User cannot make any

changes to the information.

Storage RAM memory is only used to store

the temporary information.

ROM memory is used to store permanent

information and cannot be deleted.

Speed the accessing speed of RAM is

faster, it assist the processor to boost

up the speed

Speed is slower in comparison with RAM,

ROM cannot boost up the processor speed


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Data preserving Electricity is needed in RAM to

flow to preserving information

Electricity is not needed in ROM to flow to

preserving information

structure The RAM is an chip, which is in the

rectangle form and is inserted over

the mother board of the computer

ROMs are generally the optical drivers,

which are made of magnetic tapes.

Cost The price of RAMs are

comparatively high

The price of ROMs are comparatively low

Chip size Physically size of RAM chip is

larger than ROM chip

Physically size of ROM chip is smaller than

RAM chip.

Types The RAM memory is categorized

into two types they are the: Statistic

RAM (SRAM) and Dynamic RAM

(DRAM)

The ROM memory is categorized into three

types, they are: PROM (Programmable Read

Only memory), EPROM (Erasable

Programmable Read Only memory) and

EEPROM (Electrically Erasable

Programmable Read Only memory)

computer evolution

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