Imaging DevicesImaging input Devices are devices that input images such as still photos, motion pictures, graphics, video etc. into the computer for processing.

1. Image scanner. Is a light sensing input device that converts printed texts and graphics into a digital form that can be further processed by the computer OR This is advice that is used to read graphical data or information into a computer

Common types of scanners include:• Flatbed scanner• Pen or handheld scanner• Sheet bed scanner• Drum scanner.

2. Digital Camera. These take photographs like normal cameras do. The only difference is that digital cameras do not create an image on a film like ordinary cameras but instead the image is stored on the camera and after downloaded onto a computer for editing and printing.

3. Digital video (DV) camera. A digital video (DV) camera, by contrast records video as digital signals instead of analog signals. To transfer recorded images to the computer hard disk, users connect DV cameras directly to a port on the system unit.

4. Camcorder. This is a light weight video camera that records data in digital form onto a storage device such as a videotape.

5. Web cam, also called a PC video camera, is a type of digital video camera that usually sits on top of the monitor. Some laptop computers have built-in Web cams.

Gaming input DevicesGaming input devices are devices specifically designed to be used for playing computer games.

1. Gaming keyboard2. Joysticks and wheels3. Game pad4. Light guns5. Dance pad6. Motion sensing game controllers

Audio input DevicesAudio input is the process of entering any sound into the computer such as speech, music, and sound effects. To enter sound into a computer, it must have a sound card. Audio input devices are plugged into a port on the sound card. A sound card is a device that can be slotted into a computer to allow the use of audio components for multimedia applications. Without a sound card, Audio input and output is not possible.Examples of audio input devices include

1. MicrophonesA microphone is an instrument for converting sound waves into electrical energy variations, which may then input into the computer for processing, recording or audio playback.

2. MIDI devicesMIDI (musical instrument digital interface) is the standard that defines how digital musical devices represent sound electronically such as DVD players etc.MIDI devices such as electronic pianos allow users to record and edit music

For example, you can set the beat speed, and add notes, to produce sound

3. DictaphoneThis the earliest device most commonly used to record speech for later playback or to be typed into print.

Biometric input DevicesA biometric device translates a biological personal characteristic into a digital code that is stored or compared with a digital code stored in the computer. Common biometric devices include:

1. Fingerprint scannerA fingerprint scanner captures curves and indentations of a fingerprint. Some grocery and retail stores now use fingerprint readers as a means of payment, where the customer's fingerprint is linked to an account or credit card.

2. Face Recognition systems A face recognition system captures a live face image and compares it with a stored image to determine if the person is a legitimate user.Some buildings use face recognition systems to secure access to rooms

3. Hand geometry systemsBiometric devices measure the shape and size of a person's hand using a hand geometry system. Some large companies use this system as time and attendance devices or as security devices. Day-care centers use this system to verify parents who pick up their children.

4. Signature verification systemsA signature verification system recognizes the shape of your handwritten signature, as well as measures the pressure exerted and the motion used to write the signature.

Signature verification system uses a specialized pen and tablet.5. Iris Recognition systems

These are devices that use iris recognition technology to read patterns in the iris of the eye. These patterns are as unique as a fingerprint. Iris recognition systems are used by government security organizations, the military, and financial institutions that deal with highly sensitive data.

Other Specialized input devicesThere are many other special input devices that are used for doing special customized tasks. Some of them include:

1. Remote ControlRemote control devices emit a beam of infrared light, which carries data signals.Remote control is commonly used with TVs but many laptop computers being produced come with remotes and a form of input device, which allow you to operate the laptop from a distance

2. SensorsThese are input devices that can detect external changes in the environment such as light, temperature, sound, position, humidity etc.

3. Terminals These are devices with a monitor and a keyboard. Or it can also refer to any device that sends and receives computer data. Different types of terminals include;• Dumb terminal

This has no processing power, so it must be connected to a server to operate.

• Intelligent/smart terminalThis has memory and a processor so that it can perform some functions independent of the server.

• Electronic Point of Sale terminal (EPOS)

This is used to record purchases at the point where the consumer purchases the product or service.

• Electronic Fund Transfer Point of Sale (EFTPOS)These are terminals capable of transferring funds from customer’s bank account directly to a retail outlet’s account after reading the customers debit card.

• Automatic teller machine (ATM)It is a self-service banking machine attached to a host computer through a telephone network.

PROCESSING DEVICES.

This is the heart of the computer where the entire processing takes place. It is sometimes referred to as the brain of the computer. It is the center of activities in the computer hence referred to as Central Processing Unit.

Features of the CPU

CPU is considered as the brain of the computer. CPU performs all types of data processing operations. This

involves performing logical instructions such as comparing and performing mathematical instructions such as adding and subtracting.

It stores data, intermediate results, and instructions (program).

It controls the operation of all parts of the computer.

A CPU comprises of the following parts;

1. The Arithmetic and Logic Unit (ALU):

This is the component in the CPU, which handles all the arithmetic and logic operations of the computer system. It is actually the calculator of the computer system.

2. The control unit (brain)

This is a component of the CPU which governs all activities within the computer.

It interprets instructions stored in the main memory and gives instructions to relevant parts of the computer system.

3. The registersThis is a special high speed storage area within the CPU.

Examples of registers are;

• Instruction register, which contains the instruction being

executed

• Address register, which keeps track of where a given instruction

or piece of data is stored in memory

• Storage register, which temporarily holds data taken from or

about to be sent to memory

• The Accumulator, which collects the result of computations.

• General-purpose register, which is used for several functions, as

assigned by the CU

NOTE:

The system clock; is a small chip that is used by the CPU to synchronize

the timing of all computer operations. The faster the clock, the more

instructions the CPU can execute per second.

The clock speed or clock rate of a CPU is defined as the frequency at

which a processor executes instructions or processes data. Clock speed is

measured in hertz (one cycle or tick per second). Or sometimes

measured according to the number of MIPS (millions of instructions per

second)

The machine cycle steps

- Step 1: Fetching the instruction. The instruction to be executed is

obtained from memory.

- Step 2: Decoding the instruction. The instruction is translated into

commands the computer understand and sent to the ALU.

- Step 3: Executing the instruction. The commands are carried out.

- Step 4: Storing results. The results are stored in registers or

memory.

THE SYSTEM UNIT

The system unit is a box-like case that houses the internal components of

the computer like the motherboard, the disks and drive bays, the power

supply and cooling systems etc.

A drive bay

A drive bay is a rectangular opening inside the system unit that typically

holds disk drives.

The motherboard/ system board

The motherboard is a single circuit board that provides the path through

which the processor communicates with internal and peripheral devices.

A peripheral device is any device attached externally to the system unit

to add functionality like printers, monitors, keyboards etc.

The components attached to the motherboard include the processor chip,

memory chips, support electronic circuitry, buses, and Expansion Slots

for Adapter Cards.

Expansion slots and Adapter cards

An expansion slot is a socket on the motherboard that can hold an

adapter card.

An adapter card, also called expansion card, is a circuit board that

increases the capabilities of the system or provides connections to

peripherals. Adapter cards are used for many supplemental capabilities,

such as more memory, higher-quality sound devices, a modem, extra

ports, or graphics capabilities.

Note;

Plug and Play (PnP) refers to the computer’s capability to automatically

configure adapter cards and other peripherals as you install them when

the computer is still running.

Buses

The bus is a common electrical path that enables data flow between the

various system components. There are two types of buses and these

include;

i. The data bus which transfers actual data bits

ii. The address bus which transfers information about where the data

should go in memory.

Ports

A port is the point at which a peripheral attaches the system unit.

Through a port, the peripheral can send data to or receive information

from the computer. Common ports include

Universal Serial Bus (or USB) Port; It can connect all kinds of

external USB devices such as external hard disk, printer, scanner,

mouse, keyboard, etc. they are used in high speed device

interfaces. It allows you connect several different devices using

one port.

Parallel Port. This long and slender port is also no longer

commonly used, but was the most common way of attaching a

printer to a computer until the introduction of USB ports (see

below). This parallel port can transfer eight bits of data (one byte)

simultaneously through eight separate lines in a single cable. It is

faster but it transfers data in a limited distance than the serial port.

Serial ports; it enables a line to be connected that will send bits

one at a time on a single line.

VGA Port; It is termed as video graphic array. It connects monitor

to a computer's video card. It has 15 holes.

PS/2 Port; Used for old computer keyboard and mouse green for mouse and purple for keyboard.

Fire wire Port; Transfers large amount of data at very fast speed. Connects camcorders, printers and video equipment to the computer.

Ethernet. Connects to a network and high speed Internet. This port resides on an Ethernet Card.

Digital Video Interface, DVI port; Connects Flat panel LCD monitor to the computer's high-end video graphic cards.

Connectors

A connector joins a cable to a port. A connector at one end of a cable

attaches to a port on the system unit, and a connector at the other end of

the cable attaches to a port on the peripheral.

Most connectors are available in one of two genders: male and female.

Male connectors have one or more exposed pins.

Female connectors have matching holes to accept the pins on a

male connector.

Power Supply and Cooling Technology

The power supply is the component of the system unit that converts the

wall outlet AC power of 110 to 240 volts into DC power of 0.5 to 12

volts

Built into the power supply is a fan that keeps the power supply cool.

A heat sink is a small ceramic or metal component with fins on its

surface that absorbs and disperses heat produced by electrical

components such as a processor.

MEMORY

INTERNAL MEMORY

It is a temporary memory used by the processor to store instructions to

be executed and data to be used with those instructions. While

performing a processing operation, a processor needs a place to

temporarily store instructions to be executed and the data to be used with

those instructions.

Types of memory:

The system unit contains two types of memory: volatile and nonvolatile.

A volatile memory is a type of memory that loses all its contents

when power is turned off.

A nonvolatile memory is a type of memory that retains its

contents even when poer is off

Below, we discuss these types of memory.

Random Access Memory (RAM)/ main memory/working memory

This is a type of computer memory where data or information is stored temporarily and if power is switched off all data is lost.

Types of RAM

• Dynamic RAM (DRAM) must be refreshed (or recharged) constantly by the CPU.

• Static RAM (SRAM) is faster and more reliable than any form of DRAM. The term static refers to the fact that it does not have to be re-energized as often as DRAM.

• Magneto resistive RAM (MRAM), stores data using magnetic charges instead of electrical charges. MRAM has greater storage capacity, consumes less power, and has faster access times.

• Virtual RAM (VRAM): Modern operating systems can use spare storage space on the hard disk as if it is working memory and this is referred to as Virtual memory or Virtual RAM. The area of the hard disk used for virtual memory is called a swap file.

Effects of increasing RAM

Faster web surfing. No matter how fast your internet connection is, a memory upgrade can help your browser display pages faster

Smoother multitasking. Memory upgrade is essential for smooth multitasking as it does not use the hard disk to run programs.

More efficient video editing. Because video files are very large, you will not only need a bigger hard disk but also need a bigger RAM to quick up processing

Efficient networking: a memory upgrade is essential for efficient networking. The server as well as individual PCs can be upgraded to lend more benefits for everyone.

Characteristic of RAM It is a temporary storage

The contents of the RAM can be changed or removed.

It is volatile i.e. loose data when power goes off.

It can be written on and read

Can be expanded

Functions of RAM

To store data and instructions awaiting processing

To store instructions that have been obeyed or whose parts have

been obeyed by the computer

To store the intermediate results after processing.

Read-only memory (ROM)

Read-only memory (ROM) refers to memory chips storing permanent

data and instructions. That is, the items stored in ROM chips often are

recorded when the chip is manufactured. ROM chips that contain

permanently written data, instructions, or information are called

firmware. Firmware can be read and used, but cannot be changed by

user.

Basic types of ROM

• MROM (Masked ROM); the very first ROMs were hard-wired

devices that contained a pre-programmed set of data or

instructions. These kind of ROMs are known as masked ROMs,

which are inexpensive.

• PROM (Programmable Read Only Memory); PROM is read-

only memory that can be modified only once by a user.

• EPROM (Erasable and Programmable Read Only Memory);

EPROM can be erased by exposing it to ultra-violet light for a

duration of up to 40 minutes. Usually, an EPROM eraser achieves

this function.

• EEPROM (Electrically Erasable and Programmable Read

Only Memory); EEPROM is programmed and erased electrically.

It can be erased and reprogrammed about ten thousand times.

Characteristics of ROM

Its contents can be read but can’t be written to.

It is nonvolatile.

It stores instructions permanently.

Its contents are permanent and ther4 cannot be changed

Functions of ROM

To store data and instructions that are necessary for the normal

functioning of the computer

To store the control programs that are necessary for the initial

activation of the hardware on power switch on.

RAM ROM

1. Volatile, temporary 1.Non Volatile, permanent

2. Contents lost when power goes

off

2. Contents remain when power goes

off

3. Read and Write 3. Read Only

4. Can be increased 4. Can’t be Increased5. Not installed at Factory 5. Installed at Factory Other special forms of memory

Memory cache; is a relatively small block of very fast memory

designed for the specific purpose of speeding up the internal

transfer of data and software instructions. Cache speeds up

processing time because it stores frequently used instructions and

data.

Flash memory; is a chip that retains its contents when power is

shut off. Flash memory can be erased electronically and

reprogrammed. Most computers use flash memory to hold their

startup instructions because it allows the computer easily to update

its contents and it’s also mainly used in notebook computers,

digital cameras, and Personal Digital Assistants.

CMOS (complementary metal oxide semiconductor); it is used

to store configuration information about the computer e.g. amount

of memory, disk drives, keyboard, date and time etc.

BIOS ROM; it is the type of memory that contains the Basic

Input/ Output System which is the sequence of instructions the

computer follows to load the operating system and other files when

the computer is turned on.

A BUFFER is an area of memory or storage in which data and

information is placed while awaiting to be transferred to or from an

input or output device.

SPOOLING refers to the process of putting tasks that need to be

done into a buffer until they can be executed.

Units of the computer held information

Information kept in computer memory in form of binary digits. These

are represented by 0 and 1’s. Every word or character is stored in the

computer as binary digit i.e. 0 or 1. These binary digits are abbreviated

as BITS (standard/smallest unit of a computer memory). A sequence of

8bits is called a BYTE. A nibble refers to a collection of four bytes or

characters.

The following table lists some higher storage units −

S.No

.

Unit & Description

1 Kilobyte (KB) 1 KB = 1024 Bytes

2 Megabyte (MB) 1 MB = 1024 KB

3 Gigabyte (GB) 1 GB = 1024 MB

4 Terabyte (TB) 1 TB = 1024 GB

5 Petabyte (PB) 1 PB = 1024 TB

STORAGE HARDWARE/ SECONDARY

STORAGE/AUXIALIARY STORAGE/EXTERNAL STORAGE

Secondary storage device or auxiliary storage devices are devices used to store information/data permanently even when power is switched off (its non-volatile)

TERMS TO NOTE;

• A storage medium is the physical material on which a computer

keeps data.

• Capacity is the number of bytes (characters) a storage medium can

hold.

• A Storage Device / storage media drives/ a drive reads and

writes data to and from a storage medium. Or it is a slot of opening

where a disk is inserted in the computer system.

• Reading is the process in which a storage device transfers data,

from a storage medium into memory.

• Writing is the process in which a storage device transfers these

data from memory to a storage medium.

• Access time, is a measure of the amount of time it takes a storage

device to locate an item on a storage medium.

• Transfer rate is the speed with which data, instructions, and

information move to and from a device. Transfer rates for storage

are stated in KBps (kilobytes per second)

TYPES OF SECONDARY STORAGE

1. Magnetic secondary storage devices2. Solid state secondary storage devices3. Optical secondary storage devices

MAGNETIC SECONDARY STORAGE DEVICES

Magnetic storage media represent data as magnetic spots on the tape or disk, with a magnetized spot representing a 1 bit and the absence of such a spot representing a 0 bit.

i. Magnetic tape: is a storage medium that consists of a thin tape with a coating of a fine magnetic material used for recording

digital data. A device that stores computer data on a magnetic tape is a tape drive. Magnetic tapes generally transfer data a bit slower than hard drives, however magnetic tapes are cheaper and are more durable. They use the sequential data access method and they have a limited shelf of about two years.

ii. Floppy diskette: is secondary storage medium that can be used to store data in a permanent manner. It stores data in form of tracks and sectors.But inserting a floppy disk into system we must use a floppy disk drive. The capacity of the floppy disk is 1.44MB with 3.5 inches wide.

Care for diskettes

• A floppy disk should not be exposed to heat, cold, magnetic fields and dust.

• Never leave diskettes in the disk drive. Diskettes should be rolled up and stored in pencil holders.

• Diskettes should not be inserted or removed from the drive while the red light is flashing.

• Avoid touching the inner magnetic strip of the diskette.

Advantages of diskettes

• Floppy diskettes are portable

• Floppy diskettes are cheap

• Random Data Access on a diskette is possible

• A floppy diskette can be write- protected from being changed.

Disadvantages of Floppy Disks

• Floppy diskettes are not reliable – they need to be handled with a lot of care, else risk losing data.

• Floppy diskettes are not durable.

• Data Access time is relatively slow.

• They have limited Storage capacity (only 1.44MB)

iii. Zip disks: is a high capacity floppy disk drive that is slightly larger than a normal floppy disk. They can hold 100 to 750 MBs of data, they are durable and good for backing up data however they were never popular. The Zip and jaz disks were introduced by Iomega Company in the 1994 and 1995. We must use a zip drive to insert the disk in the system.

iv. The jaz disk: Similar to the Zip drive, The Jaz drive was a removable disk storage system, introduced by the Iomega Company in 1995. The Jaz disks were originally released with a 1 GB capacity though it was also not popular. It needs a jaz drive to be inserted in the system.

v. Magnetic hard disk: is the main and usually largest data storage device in a computer. It’s a non-volatile random access digital magnetic data storage device, a hard drive is made up of platters which stores data and read/write heads to transfer data.A hard disk is generally the fastest in all secondary storage devices and has the largest data storage capacity.

Hard disks are not very portable and are primarily used internally in a computer system

Data on the hard disk is positioned in tracks and sectors so that can be easily read by the heads

Advantages of magnetic storage devices

- Inexpensive storage- There is direct access on any part of a drive- There is very fast access to data - Very large amounts of storage space

Disadvantages of magnetic storage devices

- Data can be altered by magnetic fields, dust and mechanical problems

- Gradually lose their charge over time i.e. there is data lost over time

- Hard disks eventually fail which stops the computer from working.- Easily attacked by viruses- Cannot transfer the disk to another computer easily

Types of hard disks Internal hard disk External hard disk Removable hard disk Online hard drive/ online storage

Internal hard disk interfaces include SATA (Serial Advanced Technology Attachment) EIDE (Enhanced Integrated Drive Electronics) SCSI (Small Computer System Interface)

SOLID STATE SECONDARY STORAGE DEVICES

This is a data storage medium based on electronic circuits with no moving parts. Solid state devices use a special type of memory called flash memory.

Flash memory is a type of electronically Erasable Programmable Read Only memory. Flash memory is non-volatile but data stored in it can be erased or changed.

Examples of solid state storage media

i. Memory cardii. Flash disksiii. Smart cardsiv. Solid state hard disks

OPTICAL MEDIA

Optical storage refers to recording of data by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light. The reflected light is converted into a series of bits that the computer can process.

An optical disc is a flat, round, portable storage medium made of metal, plastic, and lacquer that is written and read by a laser.

Optical discs used in personal computers are 4.75 inches in diameter. Smaller computers and devices use mini discs that have a diameter of 3 inches or less.

Care for Optical Discs

• Do not expose the disc to excessive heat or sunlight

• Do not eat, smoke or drink near a disc.

• Do not stack disks.

• Do not touch the underside of the disk.

• Always store the disc in a jewel box when not in use

• Always hold a disc by its edges.

• Do not drop the disk to the ground.

• Don't bend the disk.

Categories of Optical Discs

Two general categories are CDs and DVDs, with DVDs having a much greater storage capacity than CDs.

Examples of Optical Discs include:

• CD-ROM (compact disc read-only memory)

The contents of standard CD-ROMs are written by the manufacturer and only can be read and used. A typical CD-ROM holds from 650 MB to 1GB of data,

• Picture CD

A Picture CD is a compact disc that only contains digital photographic images saved in the jpg file format. You can purchase Picture CDs that already contain pictures. A Picture CD is a multisession disc, which means you can write additional data to the disc at a later time.

CD-R (compact disc-recordable)

CD-R (compact disc-recordable) is a technology that allows you to write on a compact disc using your own computer’s CD-R drive. Once you have recorded the CD-R, you can read from it as many times as you desire. A CD-R is a multisession optical disc which

allows you to write on part of the disc at one time and another part at a later time. However, you cannot erase the disc's contents.

• CD-RW (compact disc-rewritable)

A CD-RW (compact disc-rewritable) is an erasable multisession disc that you can write on multiple times. Reliability of the disc tends to drop, however, with each successive rewrite. To write on a CD-RW, you must have a CD-RW drive and CD-RW software. A CD-RW drive has a lower read and write speed as compared to CD-Rs

• Magneto-optical (MO) disk

This is a hybrid disk that combines the best features of magnetic and optical disk technologies. It has the erase and rewrite capabilities of magnetic disks, but it also has the very high-volume density capabilities of optical disks. MO disks are not popular because they are too expensive, and not as reliable as magnetic media.

• DVDs

DVD-ROM (digital video disc-ROM). A DVD-ROM is an extremely high capacity compact disc capable of storing from 4.7 GB to 17GB. In order to read a DVD-ROM, you must have a DVD-ROM drive, which can also read CDROMs. DVDs are also available in a variety of recordable and rewritable versions and formats such as DVD-R and DVD+R DVD+RW, DVD+RE, and DVD+RAM.

• High Capacity DVD formats

A Blu-ray Disc-ROM (BD-ROM) has storage capacities of up to 100 GB. The HD (high-density) DVD-ROM has storage capacities up to 60 GB. A mini-DVD that has grown in popularity is the UMD (Universal Media Disc), which can store up to 1.8 GB of games, movies, or music.

Other Types of Storage Media

• Punched Cards; A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions. They were used through the 20th century in unit record machines for input, processing, and data storage. Early digital computers used punched cards, often prepared using keypunch machines, as the primary medium for input and storage of both computer programs and data.

• Photographic film; Photographic film is a sheet of plastic such as polyester coated with a light sensitive emulsion, that is used to record and store photographs. Normal film is shipped in small canisters (boxes) that protect it from the light. When exposed to light, it forms an invisible image. A normal photographic film can hold up to 40 pictures

• Microfilm and Microfiche; these are media used to store microscopic images of documents on roll or sheet film. The images are recorded onto the film using a device called a computer output microfilm recorder. The stored images are so small they can be read only with a microfilm or microfiche reader. Microfilm and microfiche have the longest life of any storage medium. Libraries use these media to store back issues of newspapers, magazines, and genealogy records.