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.
Microprocessor
Main memory
Input / Output
Backing Storage
Central Processing Unit
Input
CPU
RAM
ROM
Backing Storage
Output
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
Input
CPU
RAM
ROM
Backing Storage
Output
Main Memory
• Where the computer stores programs &
data
• Types:
– RAM
• Random Access Memory
– ROM
• Read Only Memory
Main Memory
• ROM Chip
– Permanent storage
– Data is safe when computer is
switched off
– Data can not be written to ROM
• RAM Chip
– Temporary storage
– Data is lost when computer
switched off
– Data can be written to RAM
Backing Storage
Input
CPU
RAM
ROM
Backing Storage
Output
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
C
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
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
Backing Storage Requirements
Different applications need different amounts
of storage.
A page of text:
A simple graphic
A high resolution photograph
A song
A video
Input
Input
CPU
RAM
ROM
Backing Storage
Output
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
Sound Card
• Sound Card
– To input sound the
sound must be
changed from
Analogue to digital.
– The sound card
carries out the
conversion process
called sampling.
Specialised Input Devices
• Voice Recognition
• Handwriting recognition
– Good for portable systems
• OCR
– Software used to scan text.
• Specialised input devices are especially
significant for
– disabled users
– virtual reality
Input
Mouse
Output
Input
CPU
RAM
ROM
Backing Storage
Output
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
C
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
Multimedia
Multimedia computers use a wide range of
input and output devices to achieve the
highest quality.
Types of Computer
•
•
•
•
Desktop
Laptop/Notebook
Palmtop
Mainframe