Topic 3 : Hardware

All Components Of A Computer

All computers, whatever their size or function, have certain basic components. They have input devices for reading data into main memory, a central processing unit (CPU) for processing the data, output devices for printing, displaying or ouputting information, and auxiliary storage devices for permanent storage of programs and data.


The Processor

The processor has the following functions:
--> fetches the next instruction;
--> decodes the instruction,
--> executes the decoded instruction.

Most computers use integrated circuits, or chips, for their processors and main memory. A chip is about 1cm square and can hold millions of electronic components such as transistors, and resistors. The CPU of a microcomputer is called as a microprocessor. The processor and main memory of a PC are commonly held on a single board called a motherboard.

Main Memory

The program currently being executed and the data used by this program are held in main memory, which is divided into millions of individually addressable storage units called bytes. One byte can hold one character, or it can be used to hold a code representing, for example, a tiny part of a picture, a sound, or part of a computer program instruction. The total number of bytes in main memory is reffered to as the computer's memory size.

Computer mamory sizes are measured as follows:

1 Kilobyte (Kb) = 1024 bytes
1 Megabyte (Mb) = 1024 Kb = 1, 048, 576 bytes (about 1 million)
1 Gigabyte (Gb) = 1024 Mb = 1, 073,741,842 bytes (about 1 billion)
1 Terabyte (Tb) = 1024 Gb = 1, 099,511,627,776 bytes (about 1 triillion)

RAM and ROM

There are basically two kinds of main memory: Random Access Memory (RAM) which is the ordinary kind of main memory referred to above, used for storing programs which are currently running and data which is being processed. This type of memory is volatile which means that it loses all its contents as soon as the machine is switched off.

Read Only Memory (ROM) is the other type of main memory, and this is non-volatile, with its contents permanently etched into the memory chip at the manufacturing stage. It is used for example to hold the bootstrap loader, the program which runs as soon as the computer is switched on and instructs it to load the operating system from disk into main memory (RAM). It may also store fixed data associated with the computer system. In special purpose computers used in video recorders, washing machines and cars, the program instructions are stored in ROM.

Cache Memory

Cache memory is a type of very fast memory that is used to improve the speed of a computer, doubling it some cases. It acts as an intermediate store between the CPU and main memory, and works by storing the most frequently or recently used intructions and data so that it will be very fast to retrieve them again. Thus when an item of data is required, a whole block of data will be read into cache in the expectation that the next piece of data required is likely to be in the same block. The amount of cache memory is generally between 1Kb and 512Kb or more.

Disk Storage

The most common form of auxiliary storage (also known as external or secondary memory or backing store) is disk. All standalone PCs come equipped with an in-built hard disk, the capacity of which is also measured in bytes. A typical hard disk for a PC stores gigabytes, and is used for storing software including the operating system, other systems software, application programs and data for long term storage.

Floppy disks consist of a thin sheet of mylar plasticencased in a hard 3 1/2 "casing. The standard type of disk in use today has a capacity of 1.44Mb. Flash memory cards or sticks are rapidly replacing floppy disks. These can hold from 32Mb to 1Gb.



Primary and Secondary Storage

A computer's main memory (RAM) is known as primary storage. In order to execute a program, the program instructions and the data on which it is to operate .have to be loaded into main memory. Primary storage, however is volatile; when the computer is switched off, all the contents of memory are lost. This is one good reason to perform frequent saves to disk when working on, for example, a word processed document.

A more permanent, non-volatile form of storage is required by all computer systems to save software and data files. Magnetic tape, magnetic disks, CD-ROM (Compact Disk Read Only Memory), and microfilm are all examples of what is known as secondary storage.

Magnetic Disk Storage

A magnetic disk consists of two surfaces, each of which contains concentric circles called tracks. Each track is divided into sectors. If you reformat a disk that already has data on it, all the data will be erased (although you can also do a 'quick format' which erases only the file directory).

Floppy Disks

The standard 3 1/2 “floppy disk is a thin, flexible plastic disk coated in metal oxide, enclosed in a rigid plastic casing. A standard high density disk has a storage capacity of 1.44 Megabytes. The disk can be removed from the drive unit and is highly portable. Floppy disks are inexpensive but easily damaged.

Hard Disks For Microcomputers

The hard disk used with PCs consists of one or more disk platters permanently sealed inside a casing. Hard disks typically have a capacity of between 40Gb and 160Gb or more.

External hard drives, which can be plugged into a microcomputer, are available as extra storage.

Hard Disks For Minis And Mainframes

For large-scale applications storing huge amounts of data, several hard disk units will be required. The disks may be either fixed {sealed inside the unit) or removable. Fixed disks are faster, more reliable, and have a greater storage capacity.

As with other types of disk, data is stored on concentric tracks, with tracks being divided into sectors. All the tracks that are accessible from one position of the read-write heads form a cylinder; data is recorded cylinder by cylinder to minimise movement of the read-write heads, thereby minimising access time.

Optical Disks

Random access time is longer than that of a hard disk, but some optical storage is writeable or even re- writeable, CD-ROM, DVD-ROM (Read-only), CD-R, DVD-R (Writeable), CD-RW, DVD-RW (Re- Writeable).

CD-ROM

CD-ROMs can store around 680Mb of data, equivalent to hundreds of floppy disks. The data may be in text form, or may be in the form of graphics, photographic images, video clips or sound files. Although they do not transfer data as fast as a hard disk drive, their speed in increasing every year and is acceptable for most applications.

As the name suggests, the disks are read-only. When the master disk is created, a laser beam burns tiny pits in the surface of the disk, which (unlike a magnetic disk) has a single spiral track divided into sectors. To read data from the disk, a laser beam is reflected off the surface of the disk, detecting the presence or absence of pits which represent binary digits. CD- ROMs are widely used for distribution of software, multimedia files, catalogues and technical manuals.

CD-R Disks

Write Once, Read Many optical laser disks (WORM disks) look similar to CD-ROM disks, but they are often gold rather than silver in colours. An end-user company can use these disks to write their own material, typically for archiving or storing, say, graphic or photographic images which will not be changed.

CD-RW Disks

These are re-writeable disks and are more expensive than CD-R. These can be used for backing up where they may need to be overwritten.

DVD-ROM

Digital Versatile Disk Read-Only Memory. These disks are the same size as CD-ROMs and are made using similar materials and manufacturing techniques. They store about seven times as much data as a CD- ROM, because the track spacing and pit dimensions are smaller.

Flash Memory

Flash is electrically erasable programmable read-only memory (EEPROM). It is used in memory cards for peripheral devices such as digital cameras, mobile telephones, PDAs and MP3 players. It is also available as USB memory sticks and, when plugged into a computer's USB port, behaves like an external disk drive. Flash memory is inexpensive, high-capacity storage and is rapidly replacing floppy disks as portable secondary storage.

Hardware

Magnetic Tape

Magnetic tape is a non-volatile sequential storage medium consisting of a magnetic coating on a thin plastic strip. It is used for data collection, backup and archiving. Nearly all recording tape is of this type, whether used for video, audio storage or general purpose digital data storage using a computer.

Tape has been more economical than disks for archival data, but that is changing as disk capacities have increased enormously. If tapes are stored for the duration, they must be periodically recopied or the tightly coiled magnetic surfaces may contaminate each other.

Sequential Medium

A major drawback of tape is its sequential format. Locating a specific record requires reading every record in front of it or searching for markers that identify predefined partitions. Although most tapes are used for archiving rather than routine updating, some drives allow rewriting in place if the byte count does not change. Otherwise, updating requires copying files from the original tape to a blank tape (scratch tape) and adding the new data in between.

Uses of magnetic tape

Video recording

Video recording demands much higher bandwidth than audio recording and was made practical by the invention of helical scan. Early video recorders were reel-to-reel but modern systems use cartridge tapes and videocassette recorders are very common in homes and television production facilities, though many functions of the VCR are being replaced by optical disc media.

Data storage

The use of magnetic tape for data storage has
been one of the constants of the computer industry.

Tape has quite long data latency for random accesses since the deck must wind an average of ⅓ the tape length to move from one arbitrary data block to another. Most tape systems attempt to alleviate the intrinsic long latency, either using indexing, where a separate lookup table is maintained which gives the physical tape location for a given data block number, or by marking blocks with a tape mark that can be
detected while winding the tape at high speed.

Tape remains a viable alternative to disk due to its lower cost per bit. Tape has historically offered enough advantage in cost over disk storage to make it a viable product, particularly for backup, where media removability is also important. The rapid improvement in disk storage density and price, coupled with arguably less-vigorous innovation in tape storage, has reduced the market share of tape storage products.

Information is from http://en.wikipedia.org/wiki/Magnetic_tape
Pictures are searched through google

First Term Break Assessment

Q1. A computer system is made up of a hardware and software. What is meant by
a) hardware;
A computer and the associated physical equipment directly involved in the performance of data-processing or communications functions. Examples are

b) software;
Instructions for the computer. A series of instructions that performs a particular task is called a "program." The two major categories of software are "system software" and "application software." System software is made up of control programs such as the operating system and database management system (DBMS). Application software is any program that processes data for the user (inventory, payroll, spreadsheet, word processor, etc.)

Q2. Give an example of
a) an input device
A computer keyboard is a peripheral partially modeled after the typewriter keyboard. Keyboards are designed for the input of text and characters and also to control the operation of a computer.

b) an output device
A speaker is a device that converts analog audio signals into the equivalent air vibrations in order to make audible sound. A pair of speakers plugs into the computer's sound card, and their cases are shielded so that they can be placed near CRTs without causing magnetic interference.

c) a storage device
A pen drive is a flash memory card that plugs into the computer's USB port. It emulates a small disk drive and allows data to be easily transferred from one machine to another.

Q3. What is the function of the following components?
a) processor;
A program that interprets computer program instructions and processes data.

b) main memory
It determines the size and number of programs that can be run at the same time, as well as the amount of data that can be processed instantly.

c) secondary storage.
It is used to store data that is not in active use. Secondary storage is usually slower than primary storage or internal memory, but also almost always has higher storage capacity and is non-volatile which makes it perfect for the preservation of stored information in an event of power loss.

Q4. The table below contains names of several computer system components. For each component, indicate whether it is hardware or software by ticking in the correct column of the table:

Exercise 2.1

Describe THREE purposes of 'Operating System'

1) Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation. Users may also interact with the operating system by typing commands or using a graphical user interface (GUI, commonly pronounced “gooey”). For hand-held and desktop computers, the GUI is generally considered part of the operating system. For large multiuser systems, the GUI is generally implemented as an application program that runs outside the operating system.

2) The main memory of a computer (referred to as random access memory, or RAM) is a finite resource. The operating system is responsible for sharing the memory among the currently running processes. When a user initiates an application, the operating system decides where to place it in memory and may allocate additional memory to the application if it requests it. The operating system may use capabilities in the hardware to prevent one application from overwriting the memory of another. This provides security and prevents applications from interfering with one another.

3) Operating systems provide security by preventing unauthorized access to the computer's resources. Many operating systems also prevent users of a computer from accidentally or intentionally interfering with each other. The security policies that an operating system enforces range from none in the case of a video game console, to simple password protection for hand-held and desktop computers, to very elaborate schemes for use in high-security environments.

Exercise 1.2

Give two examples with its purposes of the following types of the following categories of software.

i) General purpose applications software

Microsoft Word - A word processor is a computer application used for the production (including composition, editing, formatting, and possibly printing) of any sort of printable material.

Microsoft Powerpoint - Being widely used by businesspeople, educators, and trainers, it is among the most prevalent forms of persuasion technology. It creates and edit presentations for slide show, meetings, and web pages.

ii) Special purpose applications software

Software used in hospital - This is used to store and find patient's information, patient's medical records and also the patient's family background. It can also be used to record the date of birth's, the number of accidents, the number of doctors, the number of deaths, the date the patient is released.

Software used in police headquarters - This is used to store and find criminal's profile, criminal's records, etc. It can also be used to store civilians information so that it can help the police in certain investigation.

iii) Programming languages, compilers and interpreters

C++ - The most popular languages for developing modern Windows oriented applications are C and C++. C is a language which was developed to provide sufficient generality to allow the development of any conceivable program, including specifically Operating Systems.

Javascript - It was developed by Netscape who suggest that it be used as a scripting language, but the structure and design of the languages makes it quite suitable for larger-scale application for development as well. Javascript is often used to create dynamic HTML pages that accept user input, and store data perhaps using a relational database.

iv) Operating systems

MS-DOS - The acronym for Microsoft Disk Operating System, is an operating system with a command-line interface used on personal computers. As with other operating systems such as OS/2, it translates keyboard input by the user into operations the computer can perform, it also oversees operations such as disk input and output, video support, keyboard control, and many internal functions related to program execution and file maintenance.

Windows 2000 Professional - It is designed to appeal to small business and professional users as well as to the more technical and larger business market for which the NT was designed. Windows 2000 Professional, aimed at individuals and businesses of all sizes. It will include security and mobile use enhancements. It will be the most economical choice.

v) Utility programs

Disk Cleanup - It helps free up space on your hard drive. Disk Cleanup searches your drive, and then shows you temporary files, Internet cache files, and unnecessary program files that you can safely delete. You can direct Disk Cleanup to delete some or all of those files.

Backup - The Backup utility helps you create a copy of the information on your hard disk. In the event that the original data on your hard disk is accidentally erased or overwritten, or becomes inaccessible because of a hard disk malfunction, you can use the copy to restore your lost or damaged data.

Exercise 1.1

Describe three types of hardware and their uses.

1) Floppy disk is a data storage device that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. Floppy disks are read and written by a floppy disk drive or FDD, the latter initialize not to be confused with "fixed disk drive", which is an old IBM term for a hard disk drive.

2) A computer printer, or more commonly just printer, is a device that produces a hard copy (permanent human-readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as computer peripherals, and are permanently attached by a printer cable to a computer which serves as a document source.

3)A computer keyboard is a peripheral partially modeled after the typewriter keyboard. Keyboards are designed for the input of text and characters and also to control the operation of a computer. Physically, computer keyboards are an arrangement of rectangular or near-rectangular buttons, or "keys". Keyboards typically have characters engraved or printed on the keys; in most cases, each press of a key corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence; other keys do not produce any symbol, but instead affect the operation of the computer or the keyboard itself. Roughly 50% of all keyboard keys produce letters, numbers or signs (characters). Other keys can produce actions when pressed, and other actions are available by the simultaneous pressing of more than one action key.