Computer Systems

I’m ONLY a machine!

Standard Grade Revision

Hardware

• Hardware refers to all the parts of the Computer System that we can touch.

• An item of hardware is called a device.

MicroprocessorMain memoryInput / Output

Backing Storage

Central Processing Unit

CPU

RAM

Backing Storage

Input Output

ROM

The Processor

• Carries out the actual process

• Follows a set of instructions called a program

Units of Storage

Binary Unit Value

Bit 1 or 0

Byte 8 bits

Kilobyte (KB) 1024 bytes

Megabyte (MB) 1024 Kilobytes

Gigabyte (GB) 1024 Megabytes

Terabyte (TB) 1024 Gigabytes

Main Memory

CPU

RAM

Backing Storage

Input Output

ROM

Main Memory

• Where the computer stores programs & data

• Types:– RAM

• Random Access Memory

– ROM• Read Only Memory

Main Memory

• RAM Chip– Temporary storage – Data is lost when computer

switched off– Data can be written to RAM

• ROM Chip– Permanent storage– Data is safe when computer is

switched off– Data can not be written to ROM

Backing Storage

CPU

RAM

Backing Storage

Input Output

ROM

Backing Storage

• Method used to physically store data.• Constantly increasing in capacity to meet

demands.• Magnetic Storage

– Floppy disc, Hard Disc, Magnetic Tape

• Optical Storage– CD, DVD

• Solid State– USB Flash Drive

Drive or Media

Drive Media

Magnetic Storage • Hard Disk Drive

– Usually main type of backing store– Non-removable media

• Floppy Disk – Plastic disk with rectangular cover– Removable media

• Magnetic Tape– Sequential Access– Think VHS tape– Removable media

Optical Storage

Optical Storage• CD-ROM

– Read by a laser beam that reflects of surface “pits” and “lands”

• DVD-ROM– Similar to CD but with larger capacity because of

multiple layers

• CD-Recordable (CD-R) / DVD-R– Write Once, Read Many

• CD-Rewritable (CD-RW) / DVD-RW– Still uses a laser but contents can be changed

USB Flash Drive

• Universal Serial Bus: – Computer interface used by

different devices.

• Solid State Memory– No moving parts

• Advantages– Portable– Can have large memory

(currently 8GB)– Difficult to damage

Access Types

• Random/Direct Access– Retrieves the data you want

straight away.• CD-ROM drive, Hard disc drive,

Floppy disc drive.

• Sequential Access– Move through record after record

to find the data you want.• Magnetic tape

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Capacity• The size of memory, hard disc space, floppy drive

space, programs, data files etc. are all measured by the number of bytes, kilobytes, megabytes or gigabytes (1024 megabytes) they can store.

500 floppy discs

=1 CD-ROM

Comparison of Backing Storage

• Speed (Data Transfer)• CD-R = 32x (4.6Mb Per Second)• Flash Drive = USB 2.0 (12Mbps)

• Capacity• CD-R = 750Mb• Flash Drive = 128Mb – 8Gb

• Cost• CD-R = Drive - £20 / Discs – 50p• Flash Drive = £52

Input

CPU

RAM

Backing Storage

Input Output

ROM

Input Devices (Navigational)

• Mouse

• Trackball

• Track pad

• Touch Screen

• Joystick

• SmartBoard

Input Devices (Data Input)

• Keyboard

• Graphics Tablet

• Scanner

• Digital Still camera

• Digital Video Camera

• Webcam

• Microphone

Specialised Input Devices

• Voice Recognition• Handwriting recognition

– Good for portable systems

• OCR– Software used to scan text.

• Sound Card– To input sound the sound must be changed from

Analogue to digital.– The sound card carries out the conversion process

called sampling.

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Mouse

Input

Output

CPU

RAM

Backing Storage

Input Output

ROM

Output Devices - Printers

• Laser– Fast

• 18 Pages Per Min (PPM)

– High quality– Expensive– Colour is out of most

peoples price range

• Inkjet– Slower than laser

• 2-5 Pages Per Min (PPM)

– Reasonable quality– Cheap– Most do colour as

standard

Output Devices

Comparison of Printers• Resolution

– Dots Per Inch (DPI)

• Speed– Pages Per Minute (PPM)

• Cost– Capital Cost– Running Costs

Output Devices

• Plotter

• Monitor (VDU)

• LCD– Liquid Crystal Display

• TFT– Thin Film Transistor

• Multimedia Projector

• Speakers

Output Devices

• Graphics Card– A device which controls the

quality of output on a monitor

• Sound Card– To output sound it must be

changed from digital to analogue– The sound card caries out the

conversion process called sampling

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Types of Computer

• Desktop

• Laptop/Notebook

• Palmtop