Contents

Section 1:Fundamentals of Hardware and Software

Objective 1.1: Describe a general-purpose computer system.

Objective 1.2: Explain the functions of the major hardware components of a computer system.

Objective 1.3: Outline the functions and uses of primary storage devices.

Objective 1.4: Manipulate units of storage.

Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity.

Objective 1.6: Use terms associated with storage devices.

Objective 1.7: Explain the uses of various input devices and media

Objective 1.8: State the types and functions of output devices.

Objective 1.9: Describe how data are stored and manipulated within the computer.

Objective 1.10: Interpret the hardware specifications of a computer system.

Objective 1.11: Distinguish between system programs and application programs.

Objective 1.12: Explain the functions of the Operating Systems.

Objective 1.13: Distinguish among multitasking, multiprocessing and multiprogramming.

Objective 1.14: Explain the different types of processing modes.

Objective 1.15: Distinguish between types of user interface.

Section 1:Fundamentals of Hardware and Software

Objective 1.1: Describe a general-purpose computer system.

Content: Major functions of systems: input, processing, output, storage

Notes:The major functions of a general-purpose system

The major functions of a general-purpose system are:

  • Input: involves obtaining data for processing
  • Processing: involves the manipulation of data to produce information. Manipulation means multiplying, adding, subtracting, dividing, sorting etc.
  • Output: involves sending information to users.
  • Storage: involves keeping the data on electronic storage.

Objective 1.2: Explain the functions of the major hardware components of a computer system.

Content:CPU, CU, ALU; main memory, secondary storage, input and output devices

Notes:The major hardware components of a computer system

The major hardware components of a computer system are shown in the diagram below.

Central Processing Unit (CPU)

The CPU is also called the processor. It takes raw data, follows a set of instructions (programs) and converts it into information. The CPU consists of two smaller units known as the control unit (CU) and the arithmetic and logic unit (ALU).

Control Unit (CU)

This is the main part of the CPU. It directs and coordinates all activities within the CPU. It determines the sequence in which instructions are executed. The CU executes an instruction by performing the following steps:

  1. Fetching the instructions from memory
  2. Decoding the instructions
  3. Fetching the data required by the instructions from memory
  4. Sending the data and instructions to the ALU for processing
  5. Sending the data to memory after processing

Arithmetic and Logic Unit (ALU)

The ALU performs all the arithmetic and logic functions in a computer. The arithmetic operations include addition (+), subtraction (-), multiplication (*) and division (/).

The logic functions are comparisons, such as

1

  1. Equal to (=)
  2. Not equal to (≠)
  3. Less than (<)
  4. Greater than (>)
  5. Less than or equal to (<=)
  6. Greater than or equal to (>=)
  7. AND
  8. OR
  9. NOT

1

Main Memory

Main memory is also called computer memory, immediate access storage (IMAS/IAS)or primary storage. This unit of memory is directly accessible to the CPU. It holds data and instructions that the computer is processing at the time.

Secondary Storage

Secondary storage is also called auxiliary storage, backing storage or disk storage. These devices are used to store data and instructions when they are not being processed. Secondary storage is more permanent than main memory, since data and instructions are not lost when the power is turned off. It is also much cheaper than primary storage and is unlimited since you can have as much of it as you can afford. The most commonly used auxiliary storage devices are magnetic storage (tapes and disks), optical storage (CD ROM, CD-R, DVD-ROM, DVD-R and DVD-RW and solid state memory (flash memory and USB drives).

Peripheral Devices

Peripheral devices are any device controlled or monitored by the CPU. It includes both input and output devices.

Input Devices

Input devices are any device that is used to put data and instructions into the computer. Some commonly used input devices are keyboard, mouse, joystick, digital camera, scanners, barcode readers and magnetic strips.

Output Devices

Output devices are any device that is used to get information out of a computer. Some commonly used output devices are VDU or monitor, printer, plotter, speakers and multimedia projector.

Objective 1.3: Outline the functions and uses of primary storage devices.

Content:PROM, EPROM, RAM, ROM

Notes:Primary Storage

This is a group of silicon chips that resides on the computer’s motherboard (main circuit board). Primary storage consists of two types of memory chips: RAM and ROM chips. A memory chip is an integrated circuit (IC) made up of millions of transistors and capacitors.

RAM

This chip is used to hold data and instructions (programs) temporarily while processing is taking place using that data and program. It also holds the data that results from processing – data that is waiting to be output or stored in a secondary storage device. RAM is volatile i.e. it is temporary and changeable. If the power is turned off or the computer is rebooted (started up again) all the information held in RAM will be lost.

ROM

This chip holds data and instructions necessary for starting up the computer when it is switched on. It is used to store system-level programs such as the BIOS (Basic Input Output System) program.

Variations of ROM

Programmable ROM (PROM)

This type of ROM can be programmed only once using special equipment. It is useful for companies that want to make their own ROMs from software they write themselves. If they change their code they can create new PROMs without requiring a ROM manufacturer.

Erasable programmable ROM (EPROM)

This type of ROM can be erased and reprogrammed, which makes it more useful than a PROM. EPROM chips are programmed in thesame way as PROM chips. Data is erased from this chip by exposing it to ultraviolet light of a specific frequency for a specified period of time.

Objective 1.4: Manipulate units of storage.

Content:Bistable devices, bit, byte, kilobyte, megabyte, gigabyte, terabyte, word, word size

Notes: Units of Storage

Memory is made up of bistable devices. Bistable means the components that make up memory can be set to one of two states either on or off. These two states are represented using binary digits- 0 for off and 1 for on. As such, the smallest unit of storage of memory is called a binary digit (bit). The amount of data and instructions that can be stored in primary storage or secondary storage media is measured in bytes.

Byte

A byte is made up of a combination of 8 bits and has the capacity to represent one character i.e. a letter, a number, a symbol, a punctuation mark or a blank space.

Word

A word is the amount of bits the computer can process in one operation.

Word size

A word size or word length is the number of bits in a word.

Larger Units of Storage

Name / Symbol / Number of bytes / Equal to
Kilobyte / KB / 1024 / 1024 bytes
Megabyte / MB / 1048576 / 1024 KB
Gigabyte / GB / 1073741824 / 1024 MB
Terabyte / TB / 1099511627776 / 1024 GB
Petabyte / PB / 1125899906842624 / 1024 TB
Exabyte / EB / 1152921504606846976 / 1024 PB
Zettabyte / ZB / 1180591620717411303424 / 1024 EB
Yottabyte / YB / 1208925819614629174706176 / 1024 ZB

Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity.

Objective 1.6: Use terms associated with storage devices.

Content:Magnetic tape, floppy disk, hard disk (fixed head, moving head, external), optical disks (CD, DVD), flash drive, flash memory cards, sequential access, direct access, sectors, tracks, read/write head; device interfaces such as : SCSI, IDE, SATA

Notes: Secondary Storage Media

Secondary storage devices are chosen for a particular use based on their:

  • Storage capacity (how much data the device can store)
  • Access speed ( the time needed to locate the data and transmit it to the CPU)
  • Portability ( ability to be easily removed and used on another system)
  • Cost
  • Size (necessary for storage on shelves or portability)

Magnetic tape

A magnetic tape looks like an audiocassette tape. Tapes may come in different sizes. It is used mainly to backup hard disks because it can store large amounts of data at a low cost. Accessing data on a tape is very slow since data is stored sequentially. Sequentially means that data is retrieved in the order which it was stored. As of 2008, the highest capacity tape cartridges can store 1 TB of data. A tape drive is used to read data from and write data to the tape. The tape drive may be external or built into the system unit.

Magnetic disks (Floppy disk, Hard disk)

All magnetic disks provide direct access to stored data. This means that you can go directly to specific piece of data without having to access any other either before or after the data you want.

Floppy disk

This is also called a diskette. It is a removable, flexible plastic disk, coated with a magnetisable material. The disk is held in a plastic case, usually 3.5 inches by 3.5 inches in dimension. The plastic case protects the disk from dust and grease. The floppy disk is used to store and transfer small amounts of data between computers. A 3.5 inch floppy disk holds up to 1.44 MB of data.

Data and information is written to or read from the disk by a read/write head in the disk drive held in the system unit. Data is stored on both sides of a diskette on tracks and sectors. Tracks are a set of numbered concentric rings. The tracks are also divided into wedge shaped pieces known as sectors, which are also numbered. A sector is the amount of data that can be read from or written to a disk by the computer in one read/write operation.

Before data is stored on a floppy disk, it needs to be formatted. Formattingmeans writing electronic information on the disk so that the computer can recognize the disk as a valid storage device where data can be stored. Most floppy disks are already formatted when they are purchased.If a diskette is formatted after data has been stored to it, the information will be deleted.

Hard disk

A hard disk is a thin but rigid, inflexible disk made of highly polished metal. The surface of each side of the disk (also called platters) is covered with a substance that can be magnetized. As of April 2009, the highest capacity HDDs is 2TB.There are different types of disk: moveable head, fixed head and external. Moveable head hard disks have one read/write head per disk. Fixed head disks have a read/write head for every track on the disk.

The access time (time to get data) from a spinning disk with one read/write head is a combination of:

  • Seek time – how long it takes the head to get to the right track;
  • Rotational delay or latency time – how long it takes for the data to rotate under the head; and
  • Transmission time – the time taken to read the data and transmit it to the CPU.

Consequently, the access time for a fixed disk is less than that of a moveable disk, since each track has a read/write head and this eliminates the seek time.

The external and removeable hard disks are portable hard disks that are connected to the system unit. External hard disks have very large storage capacities, up to 1.5 TB currently. They are used mainly by very large computers. Hard disks are more reliable than floppy disks since its platters are fixed and seal in a unit. Hard disks can store much more data than floppy disk and optical disks and access and transmission of data is faster.

Like floppy disks, a hard disk must also be formatted before any data can be stored on it. Formatting sets up the tracks, sectors and cylinders. A cylinder is made up of all the tracks of the same number from all the disks that make up the hard disk.

Optical Disks

Optical disks are disks that are read by laser lights. They are made from plastic. The data is stored on layers inside the plastic. CDs and DVDs are the two main types of optical disks.

Compact Disc

A Compact Disc (CD) is an optical disc used to store digital data. The physical dimension of a CD is 12 cm or occasionally 8 cm in diameter. CDs can hold up to 750 MB. They are three types of CDs: CD-ROM, CD-R and CD-RW.

CD-ROM (read only)

This type of CD is used for:

  • Storing multimedia (text, graphics, sound and videos).
  • Storing software packages for sale or distribution e.g. application software packages such as encyclopedias, word processors, training programs, games and graphics packages.

CD-R (recordable)

This type of CD is used for:

  • Storing large volumes of data that does not need to change e.g music CDs.

CD-RW (re-writeable)

This type of CD is used for:

  • Storing large volumes of data that change frequently e.g backups copies

DVD

"Digital Versatile Disc"commonly called “DVD” is an optical disc storage media that can be used for storing movies with high video and sound quality. DVDs look like compact discs, their physical dimensions are the same (12 cm or occasionally 8 cm in diameter). DVDs are encoded in a different format to CDs and they have a much higher density (more data is stored per unit area). Some DVDs are double sided i.e. they can hold data on both sides. DVDs can hold between 4.7 GB and 17 GB of data. Three types of DVDs are the DVD-ROM (read only), DVD-R (recordable) and DVD-RW (rewritable).

USB Flash drive

USB Flash drives are storage devices which consist of a small circuit board encased in a plastic or metal casing built with a USB interface. They are typically small, lightweight, removable and rewritable. As of November 2006 to present, memory capacities for USB Flash drives range from 32 MB up to 64 GB. Flash drives are more compact, generally faster, hold more data and may be more reliable (due to their lack of moving parts) than floppy disks.

Common uses

  1. Personal data transport

The most common use of flash drives is by individuals to transport and store personal files such as documents, pictures and video.

  1. Computer repair

Flash drives are used to transfer recovery and antivirus software to infected PCs.

  1. System administration

Flash drives are used by system and network administrators, who load them with configuration information and software used for system maintenance, troubleshooting, and recovery.

  1. Application carriers

Flash drives are used to carry applications that run on the server computer without requiring installation.

Flash Memory Cards

These come in the form of a card shaped like a stick of chewing gum, with dimensions 21.5 x 50 x 2.8 mm and storage capacities up to 64 GB. They are a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. They are used in PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras, mobile phones and video game consoles.

Storage Device – Capacity, Advantages and Disadvantages

Storage Device / Storage capacity / Advantages / Disadvantages
Magnetic tape / Up to 1 TB /
  • Easy to transport and store
  • Cheap
  • Mostly used for backup or archives
/
  • Provides sequential access to data stored
  • Limited shelf-life (2 years)
  • Must be stored in a suitable environment (smoke, dust, temperature and humidity must be carefully controlled)
  • Difficult to update files (cannot make changes to a record without writing over the entire tape)

Floppy disk / 1.44 MB /
  • Provides direct access to data stored
  • Small and very portable
  • Easy to store
  • Suitable for backing up small files
  • Data security (e.g. you can store small files that you don’t want other computer users to see)
/
  • Small storage capacity (unsuitable for storing files containing graphics)
  • Limited shelf-life (2 years)
  • Slow to read/write speeds

Fixed hard disks / Up to 2 TB /
  • Direct access
  • Fast data transfer speeds
  • Vast storage capacity
/
  • Not portable

Removable hard disks / Up to 1.5 TB /
  • Direct access
  • Fast data transfer speeds
  • Vast storage capacity compared to diskettes
  • portable
/
  • computer must have a USB port

Optical disks / CD: up to 8MB
DVD : up to 17 GB /
  • Direct access
  • Fast data transfer speeds
  • Vast storage capacity compared to diskettes
  • Portable
  • Can be cleaned easily with a soft cloth
  • Unaffected by magnetic fields
/
  • Data on CD-ROMs cannot be changed
  • Access times are slower than hard drives

Flash memory / Up to 64 GB /
  • Physically very small
  • Highly portable
  • High data transfer speed to PCs
  • Large storage capacity compared to diskettes
  • Direct access
/
  • May need special software to be used with PCs
  • Limited storage compared to CD or DVD

USB drive / Up to 256 GB /
  • Easy to use
  • Convenient (small size – can be placed in a pocket or on a key chain)
  • Large storage capacity compared to diskettes
  • Highly compatible - ‘plug and play’ (no software needed)
  • Fast access, direct access
  • Password protection
  • Disk write protection switch (prevents data from being accidentally written over)
/
  • May not be easily read with computers using Windows 98 or older operating systems

Notes: Device Interfaces