Fixed & Variable Length Record

1) Fixed length record
A data record that contains fixed length field.

2) Variable length record
Record with an adjustable length, the length of the field is stored within the record.

3) How data is stored in files in the form of fixed length records.
Data is stored within its length field given, it cannot be more than that. For example, if the given length field is 10 characters, which is maximum limit, the user cannot input data more that 10 characters.

4) State the design of a record format.
The format of a data record includes the name, type and size of each field in the record. For example student records, in which data fields like name, address, course, date of birth and so on.

Name	Address	Course	Date Of Birth
Ben Ramsey	17 Elmer Street, Ipswich	PD7015	17/08/73

5) Find the information on the estimation of the size of a file.
In a file of fixed length records, to estimate the file size is by multiplying the number of bytes in each record by the the number of records.

Topic 3: Hardware

All Components of a Computer

All computers has its basic components: input devices, central processing unit (CPU) output devices and auxiliary storage for permanent storage programs and data.

The processor

A processor is the logic circuitry that responds to and processes the basic instructions that drive a computer.

Its functions are to fetched the next instruction, decodes the instruction and executes the decoded instruction.




Most computers use integrated circuits for their processors and main memory. Microprocessor is the CPU of a microcomputer. The processor and main memory of a PC are commonly held on single board called motherboard.

Main memory

A storage device used by the computer to hold the currently executing program and its working data.

Computer memory size:
1 Kilobytes (Kb) : 1024 bytes
1 Megabytes (Mb) : 1024 Kb :1 048 576 bytes ( about 1 million)
1 Gigabytes (Gb) : 1240 Mg : 1 073 741 842 (about 1 billion)
1 Terabyte (Tb) : 1024 Gb : 1 099 511 627 776 bytes (about 1 trillion)

RAM and ROM

RAM and ROM are the two basic kinds of memory. RAM, Read Access Memory, the type of memory that stored programs and data which is currently in use and is volatile which means that all data is lose when the computer is shut down. ROM, Read Only Memory, the type of memory which is manufactured with fixed contents and is non-volatile, data is not lose when computer is shut down.



Cache Memory

A fast memory holding recently accessed data. It is designed to speed up subsequent access to the same data. Act as intermediate store between CPU and main memory.

As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), thus it does not have to do the more time-consuming reading of data from larger memory. The amount of cache memory generally between 1Kb and 512Kb.



Disk Storage

Disk is the most common form of auxiliary storage (external/secondary/backing). All PCs are equipped with in-built hard disk.

Primary and Secondary storage

Primary storage is data in random access memory (RAM) and other "built-in" devices.
It holds memory for a short period of time (volatile), data is lost when switch off. In order to execute the a program, the program instruction and the data on which it is operate have to be loaded into main memory.

For secondary storage, sometimes called auxiliary storage, is all data storage that is not currently in a computer's primary storage memory for example magnetic tape, hard disk, CD-ROM and other external devices.

Magnetic Disk

A flat rotating disc covered on one or both sides with some magnetisable material. The two main types are the hard disk and the floppy disk.

Data is stored on either or both surfaces of discs in concentric rings called "tracks". Each track is divided into a whole number of "sectors". Data is read and written by a disk drive which rotates the discs and positions the read/write "heads" over the desired track(s). If you reformat a disk that already has that has data on it, all data will be erased.

Floppy disk

A flexible plastic disk coated with magnetic material and covered by a protective jacket, used primarily by computers to store data magnetically. Also called diskette.
The standard floppy disk is 3 1/2 . A standard high density disk has a storage capacity of 1.44 Mb.

Although they cannot store as much data as convential disks and the data cannot be retrieved as easily, floppy disks have become extremely popular in situations where flexibility, low cost, and easy use are important. but it is easily damaged.

Hard disks for microcomputers

Hard disk used with PCs consists of one or more disk platters permanently sealed inside a casing. Hard disk typically have a capacity of between 40Gb and 160Gb or more. There is also external hard disk which can be plugged into the USB port of the microcomputer as extra storage.







Hard disks for minis and mainframes

For large scale applications (mainframe) storing huge amounts of data, several hard disks 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 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.


Magnetic tape

A storage medium used for data collection, backup and archiving.

Narrow plastic ribbon coated with an easily magnetizable material on which data can be recorded.

Data is recorded in 'frames' accross the tape with one frame representing one byte. The frames form tracks along the length of the tape, with 9 tracks being common, giving 8 data tracks and one parity track.

For mass storage on commercial mainframe computers, large reel-to-reel tapes are still used, but cartridges are becoming popular. Various types of cartridge are now standard on minicomputers and PCs, while audio cassettes were used with early home computers.

Uses of magnetic tape

Tape is cheap and convenient medium for backup and is also used for archiving past transactions or other data that may be needed again. Cartridge tape drivers are in common use for backing up the hard disk of personal computer being much more convenient than dozens of floppy disks. A cartridge tape can store several Gigabytes or data.

Optical disk

A plastic-coated disk that stores digital data, such as music or text, as tiny pits etched into the surface and is read with a laser scanning the surface. Also called laser disk.

CD, CD-ROM, DVD-ROM and DVD-Video are read-only optical disks that are recorded at the time of manufacture and cannot be erased. CD-R, DVD-R, WORM and magneto-optic (in WORM mode) disks are write-once. They are recorded in the user's environment, but cannot be erased. CR-RW, DVD-RAM, DVD-RW and MO disks are rewritable.

CD-ROM

Compact Disc Read Only Memory) A compact disc format used to store programs and data files. Holding either 650MB or 700MB. CD-ROMs are capable of delivering digitized sounds, images, and multimedia presentations.

CD-ROMs are made by "burning" a blank "CD-R" disc and sending it to a media manufacturer, which creates a master disc that is used to stamp out any required quantity. Users can also burn blank CD-Rs one at a time, using a PC or stand-alone duplicator.


CD-R disks

(CD-Recordable) A writable CD technology using a type of compact disc that can be recorded, but not erased (CD-Rs are "write once" discs). CD-R discs are used to master CD-ROMs, to back up data and to make copies of data for distribution.

CD-RW disks

These are rewritable disks and more expensive than CD-R. 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-ROM and are made up using similar materials and manufacturing techniques. However it can store data about seven times more than CD-ROM because the tracks spacing and pit dimension are smaller.

Flash Memory

Flash memory is non-volatile, which means that it does not need power to maintain the information stored in the chip. In addition, flash memory offers fast read access time. It use in memory cards for peripheral devices such as digital camera, mobile phones, 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. It is inexpensive and has high capacity.

First term Break Assessment

Question 1, What is meant by

a) Hardware - Components of a computer that can be seen and touch.

b) Software - The computer programs which is a set of instructions given to a computer.

Question 2, Give an example of

a) an input device - keyboard

b) an output device - monitor

c) secondary storage - hard disk

Question 3, What is the function of the following components?

a) processor - A processor receive instructions, decodes instructions and execute instructions.

b) main memory - Main memory consists of ROM (Read-Only Memory), RAM (Random Access Memory) and Cache memory. In ROM, if the computer is shut down the data is not lost but in RAM, data is lost when the computer is shut down. Cache memory is used to improve the speed of a computer. It does this by storing the most frequent and recently data.

c) secondary storage - This storage is used to increase the amount of memory of a computer and is used as a backup storage.

Question 4, Indicate the following computer system components whether it is a hardware or a software.

Component	Hardware	Software
1. Web browser
2. Main Memory
3. Operating system
4. Monitor
5. Scanner

Topic 2 : System Software

Three purposes of Operating system:

1) Controls the transfer of data from secondary storage (example pendrive) to memory and back again, and to managed the directory of disk so that files can be located easily.

2)responsible for allocating processing time, memory and input and output resources, and also schedules the jobs in order to prevent interruptions.

3)Act as a communicator between the user and the computer. The user gives instructions to the computer and the Operating system responds to them.

Components of a computer and modes of use

Two examples of software and its purpose:

1) General purpose applications software:
i/ Microsoft Access - Microsoft Access is a database management system software that is use to create database and programs. It consists of useful feature such as query and form. Query enables user to request a certain information from the database and form enables user to create customized screen format. Examples of database that we use are student's marks list, encyclopedias, and library catalogues.

ii/ Microsoft Excel - Microsoft Excel is a spreadsheet package which consists of number of cells arranged in rows and columns. It is usually use for calculations like making a budget. The user needs to use the formula or functions. Functions always have a key words such as SUM, AVERAGE or MAX while for formula it is a mathematical expressions that contains cell addresses for example =B2-B3.

2) Special purpose applications software:
i/ QuickBooks Simple Start Free Edition - A software that helps you to manage business tasks. Create professional-looking invoices, print checks, and track expenses quickly and easily.

ii/ Sixth Sense POS 6.x - Point of Sale software excels in retail and wholesale operations. It includes inventory management, label printing, supplier and customer tracking and much more.

3) Programming language, compilers and interpreters:
i/ PASCAL - This is a programming language that is use to teach structured programming to students.

ii/ COBOL - COBOL stands for COmmon Business Oriented Language. This programming language is invented specially for writting commercial and business.

4) Operating system:
i/Windows XP HOme Edition - a personal computer operating system from Microsoft together with some commonly use application softwares such as Microsoft Word and Microsoft Excel. It is also consists of built in networking.

ii/ Macintosh OS - Often called "The Mac" and is the first widely sold personal computer with a Graphical user interface (GUI).

5) Utility program:
i/ Disk Defragmenters - Arranging the pieces of files that are scattered all over the disk. It helps to find out how badly the files are fragmented and how much it the computer is slowed down because of it.

ii/ Anti-Virus - This is a software that helps to protect your computer from viruses. This anti-virus can detect viruses, stopped it before it can do anything that can corrupt the computer. Example of anti-virus is Norton Anti-Virus.

Computer h/w = Hardware

Types of hardware and its functions:-

1) Modem = A device that is used for internet connection using telephone line.

2) Printer = Printer is use for printing outputs such as documents and images or photos.

3) Scanner = A scanner is use to scan graphical images or photographs and documents.