COMPUTER FUNDAMENTAL | 2010 TYPE OF MEMORY & STORAGE DEVICES · PDF fileTYPE OF MEMORY & STORAGE DEVICES ... Cache are the primary memory. 3.2 Secondary storage or Auxiliary storage

COMPUTER FUNDAMENTAL | 2010

Prepared By, Hiren H Parmar & Rushabh P Madhu(9662140014)

TYPE OF MEMORY & STORAGE DEVICES

� We use memory for storing data and program in computer. Computer memory can broadly

classify in two types:

1) Primary memory 2) Secondary memory

� Primary memories are semiconductor, high speed, high cost, low capacity, volatile (temporary)

memory which CPU uses for instruction execution.

� Secondary memory also called auxiliary memory which is low speed, low cost, high capacity,

non-volatile (permanent) memory which computer uses for actual program & data storage.

� Below table show property of memory and comparison of primary & secondary memory.

3.1 Primary storage or main Memory (Semiconductor or IC memory chip)

� Processing speed of CPU is very high while access speed of secondary memory is very low.

This mismatch reduce overall speed and performance of computer so to reduce the speed

gap between memory and CPU every computer uses such a storage space, which is known

as primary storage, main memory or simply memory. It is a temporary storage area, which is

built into the computer hardware, and in which instructions and data of a program reside,

mainly when the program is being executed by the CPU.

� A main memory of a computer system is made up of several small storage areas, called

locations or cells. Each of these locations can store a fixed number of bits, called word length

of that particular memory. Each word or location has a built-in and unique number assigned

to it. This number is called the address of the location. You might have heard about 16-bit

computers, 32-bit computers, 64-bit computers etc. This refers to the word length of

memory of a particular compute. Data and instructions are moved, to and from memory in

bunches of word length.



Therefore, even if the electronic circuits used are comparable in speed, machine having smaller

word length will be slower in operation than machine having larger word length.

Fixed Word-length memory :- The main memory of many computer is designed to store a fixed

number of character (equal to its word-length in bytes) in each numbered address location. Such

computers are said to be word-addressable and they employ a fixed-word-length memory

approach. It is normally used in large scientific computers for gaining speed of calculation. Modern

computer mostly uses fixed word-length memory.

Variable Word-length memory :- In many computer, the main memory is designed in a manner

that each numbered address can only store a single character. Computer designed in this manner,

are said to be character-addressable and thy employ a variable-word-length memory approach. It

is mainly used for optimizing the use of storage space but with the memory becoming cheaper and

larger day-by-day most computer uses fixed word length memory.

Capacity of Memory :- Number of bytes a computer system can store called its memory capacity.

Memory capacity of a computer normally stated in terms of MegaBytes (MB) and GigaBytes (GB).

8 bit = 1 bytes

1024 bytes = 1 kilo bytes (KB)

1024 KB = 1 mega bytes (MB)

1024 MB = 1 giga bytes (GB)

� RAM, ROM, PROM, EPROM, Cache are the primary memory.

3.2 Secondary storage or Auxiliary storage memory

� The primary storage of a computer system has following limitations : memory

1. Limited capacity : It is often necessary to store huge amount of bytes of data in a computer.

Unfortunately , the storage capacity of the primary storage of today’s computers is not

sufficient to store the large volume of data, which needs to be handled by most data processing

centers.



2. Volatile : The primary memory is volatile, and the data stored in it is lost, when the electric

power is turned off or interrupted. However, computer systems need to store data on a

permanent basis.

� As a result, additional memory called auxiliary memory or secondary memory is used with most

computer systems. Secondary memory is non-volatile and has lower cost per bit stored, but it

generally has an operating speed far slower than that of the primary storage. Secondary storage

devices are the actual devices in which data and programs are stored. Though because of its

high access time CPU doesn’t directly use it instead it uses primary memory for program

execution & data processing. So data stored in secondary devices must first transfer into

primary memory before CPU can access it.

� Selection of secondary devices for a particular application, mainly depends upon how the stored

information needs to be accessed. There are two methods of accessing information

a) Sequential Access device

b) Direct Access device

� A sequential access storage device is one in which the arrival at the location desired may be

preceded by sequencing through other locations, so that arrival time varies according to location. In

other words, information on a sequential-access device can only be retrieved in the same sequence

in which it is stored. To access 28th

data record stored on sequential access device, the computer

must first access (although not process) the first 27 data records. This is analogous to a music tape

cassette. Suitable for such applications like preparation of monthly pay slips, or monthly electricity

bills etc. Magnetic Tape is an example of sequential storage device.



� Secondary storage devices exists, which permit access to individual information in a more direct or

immediate manner. These direct-access devices are also called random-access devices, because the

information available at random i.e. it is available in any order. Hence, a random-access devices is

one in which any location in the device may be selected at random, access to the information

stored is direct, and approximately equal access time is required for each location. This is analogous

to a music CD. It is mainly used in computerized bank, railway and airline ticket booking system

where immediate access is required by individual customers.

3.2.1 Magnetic storage devices

� Magnetic storage devices are the devices which use magnetic storage techniques for

permanently data storing.

Magnetic Tape :

� Magnetic tape is the most popular storage medium for large data, which are sequentially

accessed and processed.

� The magnetic tape medium is a plastic ribbon, which is usually 1/2 inch or ¼ inch wide, and

50 to 2400 feet long.

� It is coated with a magnetizable recording material, such as iron oxide or chromium dioxide.

� Data are recorded on the tape in the form of tiny invisible magnetized and non-magnetized

spots (representing 1s and 0s) on the coated surface of the tape.

� The tape ribbon is itself stored in reels or a small cartridge or cassette.

� Like audio or videotape, the magnetic tape used in computer systems can also be erased

and reused indefinitely. Old data on a tape are automatically erased, as new data are

recorded in the same area. However, the information stored can be read many times,

without affecting the stored data.

Basic principles of operation :

The tape of magnetic tape storage is divided into vertical columns, called frames, and

horizontal tows, called channels or tracks



� As shown in above figure tapes had 7 tracks, and they used the 6-bit BCD code format for

data recording where 7th

track is used for parity bit or check bit to detect errors. Most modern

magnetic tapes have 9 tracks & they use the 8-bit EBCDIC code format for data recording.

� A magnetic tape is a continuous medium in which data are recorded serially. There is no

addressing. In this situation, how can different pieces of data (known as records) be identified on

a tape? For this, records are separated by blank spaces on the tape, called inter-record gaps

(IRG). Each IRG is of the order of 0.5 inches.

To utilize more tape for writing records are grouped in blocks, separated by an inter-block gap

(IBG). The process of grouping two or more records together, to form a block of data, is known as

blocking, and the number of records put together n each block is called blocking factor.

Storage Capacity :- Storage capacity of a tape = Data recording density (in BPI) x length (m/ft.)

Data Transfer Rate : -It refers to the number of characters per second can be transmitted to the

primary storage from the tape. It is measured in bytes per second (bps).

Tape Drive :-A magnetic tap drive is used for storage and retrieval of data, which is stored on

magnetic tape medium. The tape drive is different from tape reels, tape cartridges, and tape

cassettes. However, all of them work on a similar mechanism like the audio tape recorders or VCR

found in our homes. Tape drive has read/write heads, and as the tape ribbon passes under the

read/write heads, the data can be either read from or written to the tape.

Tape controller :- A magnetic tape must be mounted on a tape drive, before it can be used for

reading/ writing of information. A tape drive is connected to and controlled by a tape controller.

Types of Magnetic Tapes :-

1) Half inch tape reel

A magnetic tape reel uses ½ inch tape ribbon, which is



stored on a tape reel (see figure A). The magnetic tape

drive of tape reel is shown in figure B. The tape on a

reel moves through a tape drive in much the same way

as a videotape moves through a movie projector.

During processing, the tape moves from a supply reel

to a take-up reel through a read/write head assembly.

The read/write head assembly either reads data or

writes data on the tape. It is a single unit having one

read/write head for each tape track. Therefore, the

read/write head assembly on a 9-track tape drive will

have a set of nine heads. Each head operate

independently and stores information on nine parallel

tracks, parallel to the edge of the tape. The method of

storing data in adjacent bit configurations is known as

parallel representation.

The two vacuum channels of the tape drive acting as

buffers, to prevent the tapes from snapping or

stretching when starting from a stationary position, or

slowing down from full speed.

Magnetic tape reels are fast getting replaced by other

types of tape because these new devices are more

compact, cheaper and easier to handle and use.

Figure-A

Figure-B

2) Half inch tape cartridge

Magnetic tape is used in smaller computer systems in

the form of tape cartridges. As shown in figure C,

these tape cartridges look very similar to the video

cassettes, which are used in the familiar home VCRs. A

tape cartridge can be pushed inside or ejected from

the tape drive, just as a videotape cassette.

These tape cartridges provide a more convenient way

to package tape. They also simplify the mounting of

tape & provide protection against dirt and

contamination since the tape is sealed inside the

cartridge.

Figure-C

3) Quarter-inch streamer tape

One of the primary uses of magnetic tapes is to serve as a backup storage medium for data stored

on on-line devices such as hard disk. During backup or recovery process, backup tapes are normally

processed continuously from beginning to end. Hence, there is no need to start and stop the



backup tape after every few records. A special type of quarter-inch streamer tape eliminates the

need for the start/stop operation so can read/write data more efficiently.

Streamer tapes read/write data serially as stream of bits. The data format used in these tapes has

been standardized by the industry and is known as the QIC (Quarter Inch Cartridge) standard.

4) 4mm Digital Audio Tape (DAT)

This is the most recent type of magnetic tape storage device, which provides a very high data

density per inch of tape. It uses a tape ribbon of 4mm which enclosed in a cartridge. Uses a tape

drive that uses helical scan technique for data recording. DAT drives use a data recording format

called Digital Data Storage (DDS), which provide 3 level of error-correction code. Typical capacity of

DAT cartridges varies from 4 GB to 14 GB.

Advantages :

1. Storage capacity is virtually unlimited, because as many tapes, as required, can be used.

2. Low cost of tape reels and cartridges, and high data recording densities, the cost per bit of

storage is very low for magnetic tapes.

3. Compact and light in weight

4. Easy to handle and store

5. They often used for transferring data and programs

Limitations :

1. Due to their sequential access nature, they are not suitable for storage of those data, which

frequently require to be accessed randomly.

2. Must be stored in a dust-free environment because dust can cause tape reading error.

3. Stored in an environment with properly controlled temperature and humidity otherwise the

tape ribbon may get twisted, resulting in loss of stored data

4. Must be properly labeled, so that data stored is not erased by mistake

Uses of Magnetic Tapes :

1 Applications, which are based on sequential data processing like inventory master file

periodically updated using transaction file, payroll etc.



2 Backing up data stored on on-line storage device so that if by accident, the data on the disk is

corrupted or lost, it can be retrieved from the backup.

3 Archiving of data file which are not used frequently

4 Transfer of data and program from one computer to another

5 Distribution of software

MAGNETIC DISK :

� Magnetic disk is the most popular storage medium for direct-access secondary storage. Due

to their random access capability, it becomes widely used on-line storage device.

� A magnetic disk is a thin, circular plate/platter made of metal or plastic, which is usually

coated with a magnetizable recording material, such as iron oxide. Data are recorded on the

disk in the form of tiny invisible magnetized and non-magnetized spots on the coated

surfaces. A standard 8-bit EBCDIC is used for recording. The disk itself is stored in a specially

designed protective envelope or cartridge, or several of them may be stacked together in a

sealed, contamination-free container.

� Like magnetic tapes, magnetic disks can also be erased and reused indefinitely. Old data on

a tape are automatically erased, as new data are recorded in the same area. However, the

information stored can be read many times, without affecting the stored data.

Basic principles of operation

� For data recording, the surface of a disk is divided into a number of invisible concentric

circles, called tracks. As shown in figure 8.8, the tracks are numbered consecutively from

outermost to innermost, starting from zero. The number of tracks varies greatly between

disks from 40 to several thousands. Each track is further subdivided into sectors.

Figure 8.8 Tracks on a disk. Figure 8.9 Sectors on a disk



� A sector typically contains 512 bytes. A sector is the smallest unit with which any disk can

work. That is, disk drives are designed to access (read/write) only whole sectors at a time.

Each sector is assigned a unique number. Before a disk drive can access a piece of data (a

record) stored on a disk it must specify the record’s disk address. A disk address comprised

of a sector number, track number & surface number (when double sided disks are used). It

represents the physical location of the record.

� Often multiple disks are staked and used together to create large capacity dist storage

systems where each disks is fixed to a central shaft, one below the other, to form a disk pack

(see figure 9). For faster access of data from disk pack a concept called cylinder is used for

data organization of disk pack. A set of corresponding tracks on all the recording surfaces of

a disk pack together form a cylinder. Example, the 5th

track of all recording surfaces together

form the 5th

cylinder of the disk pack.

� Storage Capacity : Storage capacity of a disk system=number of recording surfaces

x number of tracks per surface

x number of sector per track

x number of bytes per sector.

Types of Magnetic Disks:- All magnetic disks are round platters. They come in different sizes,

different types of packaging, and can be made of rigid metal or flexible plastic. They are broadly

classified into two types – floppy disks and hard disks.

A) FLOPPY DISKS

� A floppy disk is a round, flat piece of flexible plastic, coated with magnetic oxide.

� It is encased in a square plastic or vinyl jacket cover.

� The jacket gives handling protection to the disk surface.

� Moreover, it has a special liner, which provides a wiping action to remove dust particles,

which are harmful for the disk surface and the read/write head.



� Floppy disks are so called because they are made of flexible plastic plates, which can bend,

not hard plates.

� They are also known as floppies or diskettes.

� They were introduced by IBM in 1972, and are now being produced in various sizes and

capacities by many manufacturers.

Floppy disk drive:-

� A floppy-disk drive is a device, which is used to read/write data from/to floppy disks. The

drive has a spindle, which rotates the disk and read/write heads, which can move in and out

to position the read/write heads on any track of the disk surface. It is of the

interchangeable magnetic disks type. That is, it allows the loading and unloading of

magnetic disks, as and when they are needed, for reading/writing data on to them.

Types of floppy disks:-

� Floppy disks and their corresponding drives are available in two sizes i.e. 5 ¼ inch and the 3

½ inch.

1) The 5 ¼ inch diskette:- It is floppy disk of 5 ¼ inch diameter. The disk is encased in square vinyl

jacket that is harder than the disk itself but still flexible. The disk rotates inside its jacket cover

whose inner side is smooth and permits free rotation of the disk. Recall that disk density refers

to the number of bits that can be stored per square inch area on one surface of the disk.

2) The 3 ½ inch diskette:- It is the most commonly used floppy disk today. Its diameter is 3 ½ inch.

The disk is encased in a square, hard plastic jacket cover. The jacket cover has a cutout

(aperture) for the read/write head to make contact with the disk surface. This aperture is

covered with a sliding metal piece. When the diskette is inserted into the drive, this covers

slides back to expose the disk surface to the read/write head.

All 3 ½ inch floppy disks are double-sided type, and record data on both the disk surfaces.

However they come in three different capacity – double density (720- KB approximately), high

density (1.4 MB approx.) and very high density (2.88 MB Approx.)



B) HARD DISKS

Hard disks are the primary on-line secondary storage device for most computers today. Unlike

floppy disks, hard disks are made of rigid metal (frequently aluminium). The hard disk platters come

in many sizes, ranging from 1 to 14 inch diameter.

Types of hard disks :- Depending on how they are packaged, hard disks are categorized as follow :

1) ZIP DISKS:- In this type, a single hard disk platter is encased in a plastic

cartridge. A commonly used zip disk is of 3 ½ inch size, having a

storage capacity of about 100 MB, depending of the formatting style

used by a particular computer. Its disk drive is called a zip drive. A zip

drive may be of portable or fixed type. The fixed type is a part of the

computer permanently connected to it. The portable type can be

carried to a computer system, connected to it for the duration of use,

and then can be disconnected and taken away when the work is done.

The zip disks can be easily inserted into or removed from a zip drive

just as floppy disks in floppy drive.

2) DISK PACKS:- A disk pack consists of multiple hard disk platters mounted on a single central

shaft. Hence, all the disks of a disk pack revolve together at the same speed. The disk drive of a

disk pack has a separate read/write head for each disk surface, excluding the upper surface on

the topmost disk, and the lower surface of the bottommost disk. These two surfaces are not

used for data recording in a disk pack. When not in use, disk packs are stored in plastic cases.

They are of removable/ interchangeable type in the sense that they have to be mounted on the

disks drive, before they can be used, and can be removed and kept off-line, when not in use.

That is, different disk packs can be mounted on the same disk pack drive at different instances

of time. This gives virtually unlimited storage capacity to disk packs.

3) WINCHESTER DISKS:-A Winchester disk also consists of multiple hard disk platters mounted on

a single central shaft. However the main different between a Winchester disk and a disk pack is

that Winchester disks are of fixed type. That is, the hard disk platters and the disk drive are

ZIP Media



sealed together in a contamination-free container, and cannot be separated from each other.

Hence, as opposed to disk packs, which have virtually unlimited capacity, Winchester disks have

limited capacity. However for the same number of disk platters of the same size, Winchester

disk can manage to have larger storage capacity than disk packs due to the following reasons:

� Because both the disk platters and disk drive are sealed in a contamination-free container

and do not require to be separated later, all the surfaces of all the disk platters (including

the topmost surface and bottommost surface) are used for data recording in case of

Winchester disk.

� The contamination-free environment allow it to employ much greater precision of data

recording and accessing, resulting in greater density of data storage than the

interchangeable disk packs.

The storage capacity of today’s Winchester disks is measure in gigabytes.

ADVANTAGES OF MAGNETIC DISKS

1 It supports direct access of data so suitable for a wider range of applications.

2 Due to its random access property, magnetic disks are often used simultaneously by

multiple users as a shared device.

3 Magnetic disks are suitable for both on-line and off-line storage of data. Example,

Winchester disk for on-line storage while floppy, zip disk for off line storage.

4 Except for the fixed type Winchester disks, the storage capacity is virtually unlimited,

because as many disks as required can be used for storing very large data sets.

5 Due to their low cost and high data recording densities, the cost per bit of storage is low.

6 Magnet disks can be erased and reused many times.

7 Floppy disks and zip disks are compact and light weight. Hence easy to handle and store.

8 Easily portable from one plate to another. They are often used for transferring data and

program from one computer to another, which is not linked together.

9 Any information desired from disk storage can be accessed in few milliseconds, because it is

a direct access storage device. This is not possible in tape storage.

10 Data transfer rate is higher than a tape system

11 Magnetic disks are more reliable, less vulnerable to data corruption due to careless handling

or unfavorable environmental conditions than magnetic tape.

LIMITATIONS OF MAGNETIC DISKS

1 Although magnetic disks may be used for random as well as sequential data processing but

for latter type is it less efficient than magnetic tapes.

2 It is more difficult to maintain the security of information stored on magnetic disks, which

are used as shared, on-line secondary storage devices, as compared to other magnetic

storage.



3 For Winchester disk, a disk crash or drive failure often results in the loss of entire data. It is

not easy to recover the lost data so suitable backup procedures are suggested

4 some types of magnetic disks, such as disk pack and Winchester disks are not so easily

portable like magnetic tape

5 On a cost-per-bit is higher than magnetic tape

6 They must be stored in a dust free environment

7 Disks should be labeled properly to prevent erasure of useful data by mistake

USES OF MAGNETIC DISKS

1 For applications that are based on random data processing

2 As a shared, on-line secondary storage device. Winchester disks and disk packs are often

used for this purpose.

3 As a backup device for off-line storage of data so that if by accident, the data on an on-line

storage device is corrupted, can be retrieved back from the backup.

4 Archiving of data which are not used frequently.

5 Transferring of data and programs from one computer to another

6 Distribution of software by vendor. Originally sold software or software updates are

distributed by vendors on floppy or zip disks.

3.2.2 OPTICAL DISK

� It is a preferred random access medium for high capacity secondary storage, because it can store

extremely large amounts of data in a limited space. An optical disk storage system consists of

rotating disk which is coated with a thin metal or some other material that is highly reflective.

Laser beam technology is used for recording/reading of data on the disk. Due to the use of laser

beam technology, it is also known as laser disks or optical laser disks.

� Storage Organization:- An optical disk has one long track, which starts at the outer edge and

spirals inward to the center (see figure O1). This spiral track is ideal for reading large blocks of

sequential data, such as music. However, it makes for slower random access time than the

concentric tracks used by magnetic disks, whose sectors can be located faster, because they are

always found on a given track.

� Like a track on a magnetic disk, the track of an optical disk is split up into sectors, but with optical

disks, each sector has the same length, regardless of weather it is located near the disk’s center

of away. This type of data organization allows data to be packed at maximum density. However,

it requires a more complicated drive mechanism because the rotation speed of the disk must

vary; the drive must slow down the disk’s rotation speed to read sectors towards the outside of

the disk.



Figure O1

Storage capacity of an Optical Disk = Number of sectors x number of bytes per sector

Access Mechanism:- Optical disks use laser beam technology for recording / reading of data on the

disk surface. That is, the read/write head used in magnetic storage is replaced by two laser beam

sources. One laser beam is used to write data by focusing the stronger laser beam on the surface of

spinning disk and other laser beam used to read stored data by focusing less-powerful laser beam.

As shown in Figure O2, the beam strongly reflected by the coated surface know as a land and

weakly reflected by the burnt surface known as a pit, producing patterns of ON and OFF reflections

which are converted into electronic signals of binary 1s and 0s.

Figure O2

Optical Disk Drive : An optical disk has to be mounted on an optical disk drive, before it can be used

for reading or writing of information. An optical disk drive contains all the mechanical, electrical and

electronic components for holding an optical disk, and for reading or writing of information on to it

as shown below:

Figure O3

Types of Optical Disks :-



3.2.3.1 Compact Disks (CD-ROM, CD-R, CD-RW)

Compact Disks (CDs):- All CDs are round platters. There are different types of CDs available in

market among them CD-ROM, CD-R, CD-RW & DVD are the most popular types of CDs.

Types of Compact Disks:-

CD-ROM:- CD-ROM stands for Compact Disk-Read Only Memory. It is a shiny, silver color metal disk.

Disks are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminium to

make a reflective surface. The most common size of CD-ROM disc is 120 mm in diameter. It has a

storage capacity of 650 MB-700 MB. It is so called, because of its enormous storage capacity on a

compact-size disk, and because it is a read-only storage medium. The information stored on them

cannot be altered.

It is a spin-off of music CD technology, and works much like the music CDs. You can play it on your

computer with multimedia support. It is widely used for software distribution & backing up data.

CD-R:- A CD-R (Compact Disc-Recordable) is a variation of the Compact Disc invented by Philips and

Sony. CD-R is a Write Once, Read Many optical medium (though the whole disk does not have to be

entirely written in the same session). A standard CD-R is a 1.2 mm thick disc made of polycarbonate

with a 120 mm or 80 mm diameter. It has a storage capacity of 74 minutes of audio or 650 MB of

data.

CD-RW :- Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. Known as CD-

Erasable (CD-E) during its development, CD-RW was introduced in 1997. CD-RW discs are usually

produced in the most common CD-R disc capacities such as 650 and 700 MB. CD-RW recorders

typically handle the most common capacities best. In theory a CD-RW disc can be written and

erased roughly 1000 times, although in practice this number is much lower. CD-RW discs need to be

blanked before reuse. Different blanking methods can be used, including "full" blanking in which

the entire surface of the disc is cleared, and "fast" blanking in which only meta-data areas are

cleared. One important difference between R and RW media is that the re-crystallized alloy of RW

media will gradually decrystallize over time so not reliable for long time data storage than CD-ROM.

3.2.3.2 DVD (Digital Versatile Disk)

Digital Versatile disk is an optical disk storage media format that can be used for data storage,

including movies with high video and sound quality. DVD uses the same principle as a CD for

reading and writing.

Working:-

� In DVD a smaller wavelength laser beam (650 nm) is used

� A lens system is used to focus the laser beam which can focus on two different layers on the

disk

� On each layer data is recorded thus, the capacity can be doubled



� Further the recording beam is sharper compared to CD and the distance between successive

tracks is also small.

� In both CDs and DVDs the density of data stored (pits and lands per unit length) is constant

throughout the spiral track.

� The total capacity of DVD is 4.7 GB or Dual layer DVD is 8.5 DB

Advantage: -larger storage capacity

-Widely used off-line storage device for software distribution and backing up data.

Limitation: -More expensive

-Can be damaged if not handled properly like CDs.

3.2.3 Pen Drive

Pen drive is a type of Flash memory also called USB flash drives

which uses NAND-type flash memory data storage devices integrated

with a USB (universal serial bus) interface. They are typically small,

lightweight, removable and rewritable. As of April 2007, memory

capacities for USB Flash Drives available up to 64 gigabytes.

USB flash drives offer potential advantages over other portable

storage devices, particularly the floppy disk. They are more compact,

faster, hold more data, and are more reliable due to their lack of

moving parts, and more durable design. Additionally, it has become

increasingly common for computers to ship without floppy disk

drives. USB ports, on the other hand, appear on almost every

current mainstream PC and laptop. These types of drives use the

USB mass storage standard, supported natively by modern

operating systems such as Windows, Mac OS X, Linux, and Unix.

A flash drive consists of (as shown in figure) a small printed circuit

board typically in a plastic or metal casing, making the drive sturdy

enough to be carried about in a pocket, as a key fob, or on a

lanyard. Only the USB connector protrudes from this protection,

and is usually covered by a removable cap. Most flash drives use

a standard type-A USB connection allowing them to be

connected directly to a port on a personal computer.

PORT Introduction:

Ports are sockets usually mounted on the back of computer. We plug cables into these ports to

connect peripherals such as printers or modems. Serial port, Parallel port, PS/2 port, USB port are

the most common ports found on PC.

1 USB connector USB mass

2 storage controller device

3 Test points

4 Flash memory chip

5 Crystal oscillator

6 LED

7 Write-protect switch

8 Space for second flash memory chip

Prepared By, Hiren H Parmar & Rushabh P Madhu

1) Serial Port :-

It is also known as asynchronous port or RS

port is a serial communication

information transfers in or out one

history of personal computers

connected the computer to devices such as

keyboards, and other peripheral

While such interfaces as Ethernet

serial stream, the term "serial port" usually identifies hardware more or

less compliant to the RS-232

modem or with a similar communication device.

and Windows environments refer to serial ports as

ports: COM1, COM2, etc.

For many computer peripheral devices the

most modern computers are connected to devices through a USB connection. The serial port is

omitted for cost savings, and is considered to be a

found in industrial automation systems and some industrial and consumer products. Network

equipment (such as routers and switches) often

still used in these areas as they are simple, cheap and allow interoperability between devices. The

disadvantage is slower communication as serial communication and

may require expert knowledge an

2) Parallel Port :-

A parallel port is a type of socket found on

interfacing with various peripherals. It is also known as a printer port or

Centronics port. This type of port normally reserved for printer and some

type of external storage device

path so they are faster way for the computer communicates with input

and output devices. One disadvantage of this port is their signal travelling

capacity is less than serial port.

environments refer to parallel

For the most part, the USB

parallel port — as of 2006, most modern printers are connected through a

USB connection. On many modern computers, the parallel port is omitted

for cost savings, and is considered to be a

3) PS/2 Port :-

The PS/2 connector is used for connecting a

compatible computer system. Its name comes from the

COMPUTER FUNDAMENTAL

Rushabh P Madhu(9662140014)

It is also known as asynchronous port or RS-232 port. In computing, a serial

serial communication physical interface through which

information transfers in or out one bit at a time. Throughout most of the

personal computers, data transfer through serial ports

connected the computer to devices such as terminals or modems. Mice

peripheral devices also connected in this way.

Ethernet, FireWire, and USB all send data as a

, the term "serial port" usually identifies hardware more or

232 standard, intended to interface with a

or with a similar communication device. The Microsoft MS-DOS

environments refer to serial ports as COM (communication)

For many computer peripheral devices the USB interface has replaced the serial p


omitted for cost savings, and is considered to be a legacy port. However serial ports can still be


equipment (such as routers and switches) often have serial ports for configuration. Serial ports are


slower communication as serial communication and setting up serial connections

may require expert knowledge and complex commands if poorly implemented.

A parallel port is a type of socket found on personal computers for


This type of port normally reserved for printer and some

type of external storage devices. They carry 8 bits at a time on parallel



capacity is less than serial port. The Microsoft MS-DOS and Windows

parallel ports as LPT ports: LPT1, LPT2, etc.

interface has replaced the Centronics-style

, most modern printers are connected through a

On many modern computers, the parallel port is omitted

for cost savings, and is considered to be a legacy port.

is used for connecting a keyboard and a mouse to a PC

computer system. Its name comes from the IBM Personal


, a serial

physical interface through which

at a time. Throughout most of the

, data transfer through serial ports

Mice,

all send data as a

, the term "serial port" usually identifies hardware more or

standard, intended to interface with a

DOS

(communication)

interface has replaced the serial port — as of 2007,


. However serial ports can still be


nfiguration. Serial ports are


setting up serial connections

d complex commands if poorly implemented.

for


This type of port normally reserved for printer and some

s. They carry 8 bits at a time on parallel



Windows

style

, most modern printers are connected through a

On many modern computers, the parallel port is omitted

PC

IBM Personal

A serial port

A Parallel port

PS/2 port



System/2 series of personal computers, with which it was introduced in

1987. The PS/2 mouse connector generally replaced the older DE-9 RS-232

"serial mouse" connector, while the keyboard connector

replaced the larger 5-pin DIN. The keyboard and mouse

interfaces are electrically similar with the main difference

being that open collector outputs are required on both

ends of the keyboard interface to allow bidirectional

communication. Normal desktop motherboards will not

identify the keyboard and mouse if they are placed on each

other's sockets.

PS/2 keyboard and mouse connectors were color-coded: purple for keyboards and green for

mice as defined by the Microsoft PC 97 standard. It does not support hot swapping, i.e. not

allowing devices to be connected and disconnected without rebooting the computer.

4) USB :-

Universal Serial Bus (USB) is a serial bus standard to interface devices.

USB was designed to allow peripherals to be connected using a single

standardised interface socket, to improve plug-and-play capabilities by

allowing devices to be connected and disconnected without rebooting

the computer (hot swapping). Other convenient features include

powering low-consumption devices without the need for an external

power supply and allowing some devices to be used without requiring

individual device drivers to be installed. USB port supports three data

rate, low speed support speed upto 1.5 Mbit/s (Mega bits per second),

full speed support speed upto 12 Mbit/s and hi-speed support 480 Mbit/s

USB is intended to help retire all legacy serial and parallel ports. USB can

connect computer peripherals such as mouse devices, keyboards, PDAs,

gamepads and joysticks, scanners, digital cameras and printers. For many

of those devices USB has become the standard connection method. USB is

also used extensively to connect non-networked printers; USB simplifies

connecting several printers to one computer. USB was originally designed

for personal computers, but it has become commonplace on other devices

such as PDAs and video game consoles.

The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards

body incorporating leading companies from the computer and electronics industries.

An USB system has an asymmetric design, consisting of a host controller with multitude of

downstream USB ports, and multiple peripheral devices connected in a tiered-star topology.

Modern computers often have several host controllers, allowing a very large number of USB devices

to be connected.

The color-coded PS/2 connection ports

(purple for keyboards and green for mice)

A USB Series “A” Plug

Different types of USB plug



1. Computer Languages

� A language that is acceptable to a computer system is called computer language or

programming language and the process of writing instructions in such a language is called

programming or coding.

� A language is a means of communication. We use a natural language, such as Gujarati,

English to communicate our ideas and emotions to others. Similarly, a computer language is

used by a programmer to instruct a computer what he/she wants it to do.

� Computer languages can broadly classify in two types

A) Low level language : Which is machine dependent, such as machine language & assembly

language

B) High level language: Which is machine independent, such as BASIC, FOXPRO

Machine level language

� This is a sequence of instructions written in the form of binary numbers consisting of 1s, 0s

to which the computer understand and responds directly. The machine language was

initially referred to as code, although now the term code is used more broadly to refer to

any program text. This is called first generation language.

� An instruction prepared in any machine language will have at least two parts, see Figure 1.

The first part is the command or operation, which tells the computer what function, is to be

performed. All computers have an operation code for each of its functions. The second part

of the instruction s the operand or it tells the computer where to find or store the data that

has to be manipulated.

OPCODE (Operation Code) OPERAND (Address / Location)

Figure 1. Instruction format

Example :- A machine language program for adding two numbers

0011 1110 Load A register with

0000 0111 value 7

0000 0110 Load B register with 10

0000 1010 A <- A + B

1000 0000 Store the result

0011 1010 into the memory location

0110 0110

0000 0000 whose address is 100 (decimal)

0111 0110 Halt processing

Advantages : - 1. Very fast execution, because computer directly understand it

2. No need of any translator

Disadvantages:-

1. Machine dependent, program made for one type of machine not works on other type.



2. Must have hardware knowledge

3. Difficult to program

4. Error prone

5. Difficult to modify

Assembly Language

� When we employ symbols (letter, digits or special characters) for the operation part &

address part of the instruction code, this representation is called an assembly language

program. This is considered to be the second generation language.

� Each machine has its own assembly language which is dependent upon the internal

architecture of the processor. Symbolic operation code called mnemonic code.

Mnemonic Code Symbolic Address

Figure 2. Instruction format

Example :- A assembly language program for adding two numbers

LDA, 7 Load A register with 7

LDB, 10 Load B register with 10

ADD A, B A <- A + B

LD(100), A Save the result in the location 100

HALT Halt processing

Assembler : -

� As assembly language program cannot be executed by computer directly as it is not in a

binary form (machine language). Hence assembly language program must be converted

(translated) to binary form. This translation is done with the help of translator program,

which is known as an assembler.

� Assembler is system software, supplied by the computer manufacturer, which translate an

assembly language program into an equivalent machine language program which computer

understands. The translated program called object program, see Figure 3.

Assembly language program � Assembler � Object code in machine

language

Figure 3. Assembler

Advantages : - 1. Easy to understand

2. East to locate and correct error

3. Easy to modify

4. No worry about addresses

Disadvantages:-1. Machine dependent

2. Knowledge of hardware required



High-level Language

� The time and cost of creating machine and assembly languages was quite high as required

for each type of computers. And this was the prime motivation for the development of high

level languages.

High level languages are characterized by the following features:

� They are machine independent. That is, a program written in a high-level language can be

easily ported and executed on any computer, which has the translator software for the high-

level language.

� It allows the programmers to mainly concentrate on the logic of the problem, rather than be

concentrated with the details of the internal structure of the computer.

� The instruction of high level language written using English word and familiar mathematical

symbols and expressions. Each statement of high-level language is normally a macro

instruction which is translated into several machine language instructions. BASIC code for

adding of two numbers & give sum.

Example. 10 LET X =7 , Y = 10

20 LET SUM = X + Y

30 PRINT SUM

COMPILER:-

� Since a high level source program must be translated first into the form the computer can

understand, this is done by software called compiler which takes the source code as input

and produce and output the machine language code of the computer which it is to be

executed. During the process of translation, the compiler reads the source program

statement-wise and checks the syntax errors. If there is any error, the computer generates

list of the errors it has detected. This action is known as diagnostics, see Figure 4.

High-level language program � Compiler � Object code in machine

language

Figure 4. Compiler

INTERPRETER:-

� There is another type of software which also does the translation of high-level language into

object code line by line called an Interpreter. Each time the program is executed, every line

is checked for syntax error and then converted to equivalent machine code. It hake more

execution time but good for fast debugging, see Figure 5.

High-level language program � Interpreter � Object code in machine

language

Figure 5. Interpreter



Advantages : - 1. Readability: program written in high-level language is more readable

2. Portability: program can run on different machine

3. Easy debugging : Error could easily be removed

4. Easy software development

Disadvantages:-1. Less efficient than machine language

2. Take more execution time

What is Operating System ?

� An operating system is an essential component of a computer system. The primary

objective of operating system is to make computer system convenient to use and utilize

computer hardware in an efficient manner.

� An operating system is a large collection of software which manages resources of the

computer system such as memory, processor, file system and input/output devices. It keeps

track of the status of each resource and decides who will have a control over computer

resources, for how long and when.

From the above figure , it is clear that operating system directly controls computer hardware

resources. Other programs rely on facilities provided by the OS to gain access to computer system

resources. There are two ways one can interact with operating system:

1) By means of operating system call in a program

2) Directly by means of operating system commands.

Types of operating system

1. Batch Operating System:-

� In this type of operating system utilization of computer resources and improvement in

programmer’s productivity is achieved by jobs with similar requirements were batched

together and run through the computer as a group.



� It is requires grouping of similar job which consist of programs, data and system commands.

The suitability of this type of processing is in programs with large computation time with no

need of user interaction / involvement. Some examples of such programs include payroll,

forecasting, statistical analysis and large scientific number crunching programs. Users are

not required to wait while the job is being processed. They can submit their programs to

operators and return later to collect them.

� Since there is only one program in the execution at a time, there is no competition for I/O

devices. Jobs are typically processed in the order of submission that is FIFO (first in first out)

basis. Processing scheduling, memory management, file management and I/O management

in batch processing are quite simple.

Advantages :

1) High utilization of computer resources

2) Simple processing scheduling, memory management, file management, I/O management etc.

3) After input process is over, while processing is going on, use can attend other jobs

Disadvantages :

1) Turn around time is very long

2) Difficult to provide process priority

3) It is not very convenient for program development

2. Multiprogramming Operating System:-

� In order to increase the resource utilization & to support simultaneously interactive users,

system supporting multiprogramming approach allow more than one program to utilize CPU

time at any moment. Thus more programs competing for system resources, better will be

resource utilization.

� The main memory of a system contains more than one program. The operating system picks

one of the programs and start executing. During the execution process program 1 may need

some I/O operation to complete that time OS will simply switch over to the next program &

so on. If there is no other new program left in the memory, the CPU will pass its control back

to the previous programs.

� Multiprogramming has a significant potential for improving system throughput and

resources utilization with very minor difference.

Multitasking OS :- A running state of a program is called a process or a task. A multitasking OS

also called multiprocessing OS, supports two or more active processes simultaneously. It is one

of the mechanism that multiprogramming OS employs.

Multiuser OS :- It allow simultaneous access to a computer system through two or more users.

Like railway reservation system.



3. Time Sharing System: It is a form of multiprogrammed OS which operates in an interactive

mode with a quick response time. A time sharing system allows the many users to

simultaneously share the computer resources. The basic idea behind time sharing system is to

allow all user programs to have a share of CPU time in turn. Each user program, starting from

first and proceeding through the last, is allocated a very short period of CPU time one by one

(called round robin scheduling). This short period of time during which user gets the attention

of the CPU is known as time slice or time slot and it is of the order of the 10 to 20 milliseconds.

As the CPU switches rapidly from one user to another, each user is given impression that he has

his own computer, which it is actually one computer shared among many.

Advantages :

1) Turn around is less

2) Computing cost is very less

3) All program / user get equal attention and small program get over fast

4) Reduce CPU idea time

Disadvantages :

1) OS is more complicated and need more memory

2) Question of security: since hundreds of users use time sharing system simultaneously,

provision must be made to protect the security and integrity of user programs and data.

3) Require data communication facilities as the users interact with the main computer

through remote terminal

4. On-line processing system:

Online processing is also known as direct access or random access processing. The main feature

of this system is to get immediate and direct access to record. In an online system the terminal

used by the operator is connected to the main computer so that the operator can interact with

the computer in a conversational mode. It is used in applications requiring fast response from

the computer e.g. Air-line reservation system.

Advantages :

1) Turn around time is negligible

2) Access and retrieval of any record is quick and direct

3) Get latest updated details

Disadvantages :

1) OS is more complicated and costly

2) Question of security

3) Data transmission facility required

4) High cost of hardware & software

5. Real time processing system:

� It is another form of OS which are used in environments where a large number of events

mostly external to computer systems, must be accepted and processed quickly or within



certain deadlines. Examples of such applications are flight control, real time simulations etc.,

frequently used in military application.

� A primary objective of real-time system is to provide quick response times. User

convenience and resource utilization are of second concern. In the real-time system each

process is assigned a certain level of priority according to the relative importance. The

processor is normally allocated to the highest priority process amount those which are

ready to execute.

� In real-time OS most of times, processes remain in primary memory in order to provide

quick response time. Time critical device management is one of the main characteristics of

real-time systems. It concern with speed and not efficient utilization of resources.

Advantages_____ :

1) Quick response time

2) Very fast data processing

3) Convenience of use, any time any where

Disadvantages ___:

1) Very expensive

2) Complicated system

3) Communication facility required

Applications _____:

1) Air traffic control system

2) To control satellite operations

3) In chemical process control system

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COMPUTER FUNDAMENTAL | 2010 TYPE OF MEMORY & STORAGE DEVICES · PDF fileTYPE OF MEMORY & STORAGE DEVICES ... Cache are the primary memory. 3.2 Secondary storage or Auxiliary storage