The components of a computer

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        The components of a computer
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Types of computer
Computers can be categorised into four types

• Microcomputers
• - desktop, laptop, notebook and palmtop
  personal computers (PCs)
• - used in businesses, schools/colleges and
  homes - cost from a few hundred pounds to a few
  thousand
• Minicomputers
• - often used as multi-user systems, with 100s
  of workstations or terminals
  attached to a central minicomputer, e.g.
  EPOS. - cost from 10,000 to about 150,000.
• Mainframe computers
• - used by large organisations which may have
  1000s of terminals, often remote - cost
  hundreds of thousands
• Supercomputers
• - largest category of computer used mostly by
  scientific industrial research departments,
  NASA, the Weather Centre, stock exchanges - cost
  millions

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CPU

• Controls the transmission of data from input
  devices to memory
• Processes the data held in main memory
• Controls the transmission of information from
  main memory to output devices

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How CPUs work?

A microprocessor -- also known as a CPU or
central processing unit -- is a complete
computation engine that is fabricated on a single
chip.
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• Using its ALU (Arithmetic/Logic Unit), a
  microprocessor can perform mathematical
  operations like addition, subtraction,
  multiplication and division. Modern
  microprocessors contain complete floating point
  processors that can perform extremely
  sophisticated operations on large floating point
  numbers.
• A microprocessor can move data from one memory
  location to another.
• A microprocessor can make decisions and jump to
  a new set of instructions based on those
  decisions.

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Clock Speed

• To synchronize the steps of the fetch-decode
• execute cycle, all processors have an internal
• clock which generates regularly timed pulses.
• All activities of the fetch-decode-execute
• Cycle must begin on a clock pulse.

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Word Size

• The number of bits that the CPU can process
  simultaneously. Normally groups of 8, 16, 32,
  64, 128 bit words are processed as a unit during
  input, output and logic instructions.
• Word size is a major factor in determining the
  speed of a processor.

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Bus Size

• Buses are the lines along which data is
  transmitted. This data can be in the form of
  data and instructions as well the addresses of
  the data and the instructions.
• The width of a data bus determines how many bits
  can be transmitted simultaneously and the maximum
  address which can be referenced.

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Bus Size cont

• For 8 bits 28 1 255
• i.e. 0 to 255 which is 256 locations.

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• An address bus (that may be 8, 16 or 32 bits
  wide) that sends an address to memory
• A data bus (that may be 8, 16 or 32 bits wide)
  that can send data to memory or receive data from
  memory
• An RD (read) and WR (write) line to tell the
  memory whether it wants to set or get the
  addressed location
• A clock line that lets a clock pulse sequence the
  processor
• A reset line that resets the program counter to
  zero (or whatever) and restarts execution

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Instruction Set

• Instructions in machine language are in the form
  of binary codes, with each different processor
  using different codes for the instruction set
  supported by its hardware.

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• The instruction set for a typical computer
• includes the following types of instructions
• Data Transfer
• Arithmetic Operations
• Logical Operations
• Test and Branch Instructions

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Main memory

• Instructions and data are held in main memory,
  which is divided into millions of
  individually-addressable storage units called
  bytes.
• One byte can hold one character, or it can be
  used to hold a code representing, for example, a
  tiny part of a picture, a sound, or part of a
  computer program instruction.
• The total number of bytes in main memory is
  referred to as the computers memory size.
  Computer memory sizes are measured as follows
• 1 Kilobyte (Kb) 1000 bytes (to be exact, 1024
  bytes)
• 1 Megabyte (Mb) 1,000,000 (1 million) bytes
• 1 Gigabyte (Gb) 1,000,000,000 (1 billion)
  bytes
• 1 Terabyte (Tb) 1,000,000,000,000 (1 trillion)
  bytes

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Random Access Memory (RAM)

• Ordinary memory
• Used for storing programs which are currently
  running and data which is being processed.
• This type of memory is volatile - it loses all
  its contents as soon as the machine is switched
  off.

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Read Only Memory (ROM)

• Non-volatile, with contents permanently etched
  into the memory chip at the manufacturing stage
• Used for example to hold the bootstrap loader,
  the program which runs as soon as the computer is
  switched on and instructs it to load the
  operating system from disk into memory.

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PROM

• Short for programmable read-only memory, a memory
  chip on which data can be written only once. Once
  a program has been written onto a PROM, it
  remains there forever. Unlike RAM, PROMs retain
  their contents when the computer is turned off.
  The difference between a PROM and a ROM
  (read-only memory) is that a PROM is manufactured
  as blank memory, whereas a ROM is programmed
  during the manufacturing process.

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• To write data onto a PROM chip, you need a
  special device called a PROM programmer or PROM
  burner. The process of programming a PROM is
  sometimes called burning the PROM.
• An EPROM (erasable programmable read-only memory)
  is a special type of PROM that can be erased by
  exposing it to ultraviolet light. Once it is
  erased, it can be reprogrammed. An EEPROM is
  similar to a PROM, but requires only electricity
  to be erased.

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• What is an EPROM?
• EPROM(Erasable Programmable Read Only Memory) can
  be programmed and erased enabling them to be
  re-used. Erasure is accomplished using an UV
  (Ultra Violet) light source that shines through a
  quartz erasing window in the EPROM package.

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• Acronym for erasable programmable read-only
  memory, and pronounced ee-prom, EPROM is a
  special type of memory that retains its contents
  until it is exposed to ultraviolet light. The
  ultraviolet light clears its contents, making it
  possible to reprogram the memory. To write to and
  erase an EPROM, you need a special device called
  a PROM programmer or PROM burner.
• An EPROM differs from a PROM in that a PROM can
  be written to only once and cannot be erased.
  EPROMs are used widely in personal computers
  because they enable the manufacturer to change
  the contents of the PROM before the computer is
  actually shipped. This means that bugs can be
  removed and new versions installed shortly before
  delivery.

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• What is an EEPROM?
• Pronounced double-ee-prom or e-e-prom, short
• for electrically erasable programmable read-
• only memory. EEPROM is a special type of
• PROM that can be erased by exposing it to an
• electrical charge. Like other types of PROM,
• EEPROM retains its contents even when the
• power is turned off. Also like other types of
• ROM, EEPROM is not as fast as RAM. EEPROM
• is similar to flash memory (sometimes called
• flash EEPROM). The principal difference is that
• EEPROM requires data to be written or erased
• one byte at a time whereas flash memory allows
• data to be written or erased in blocks. This
• makes flash memory faster.

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• What is a Flash EPROM?
• A flash EPROM is similar to an EEPROM except that
  flash EPROMs are erased all at once while a
  regular EEROMs can erase one byte at a time. In-
  circuit writing and erasing is possible because
  no special voltages are required. To accomplish
  in-circuit operation, you have to write special
  application software routines. Flash EPROMs are
  also called nonvolatile memory..

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Cache Memory

• Very fast memory used to improve the speed of a
  computer, doubling it in some cases
• Acts as an intermediate store between the CPU and
  main memory
• Stores the most frequently or recently used
  instructions and data for rapid retrieval
• Generally between 1Kb and 512Kb
• Much more expensive than normal RAM

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Memory Cache speeds up a computer by storing data
the computer has recently used. There are 2
types Internal External
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External Cache If the computer cannot find what
it needs in the Internal Cache, it looks in the
external cache. This is usually located on the
Motherboard. In some CPU chips the External
cache is built in.
Internal Cache When the computer needs data it
first looks in the Internal cache. This is
located on the CPU chip and provides the fastest
way for the computer to get data.
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Virtual memory
Space on a hard disk used to temporarily store
data and swap it in and out of RAM as needed.
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Motherboard
This is the main circuit board that all of the
other internal components connect to. The CPU
and memory are usually on the motherboard. Other
systems may be found directly on the motherboard
or connected to it through a secondary
connection. For example, a sound card can be
built into the motherboard or connected through
PCI (Peripheral Component Interface).
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Auxiliary Storage

• Hard disks
• - all standalone PCs have in-built hard disk
• - typical capacity for Pentium PC is gt 40 Gb
• - used for storing software including the
  operating system,
• other systems software,
  application programs and data
• Floppy disks
• - thin sheet of mylar plastic in hard 3½
  casing
• - capacity 1.44Mb
• CD-ROM
• - holds about 700Mb
• Zip disks
• - hold up to 250Mb

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Power supply An electrical transformer regulates
the electricity used by the computer.
Hard disk This is large-capacity permanent
storage used to hold information such as programs
and documents.
Operating system This is the basic software that
allows the user to interface with the computer.
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Integrated Drive Electronics (IDE) Controller
This is the primary interface for the hard
drive, CD-ROM and floppy disk drive.
Peripheral Component Interconnect (PCI) Bus The
most common way to connect additional components
to the computer, PCI uses a series of slots on
the motherboard that PCI cards plug into.
SCSI Pronounced "scuzzy," the small computer
system interface is a method of adding additional
devices, such as hard drives or scanners, to the
computer.
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AGP Accelerated Graphics Port is a very
high-speed connection used by the graphics card
to interface with the computer.
Sound card This is used by the computer to
record and play audio by converting analog sound
into digital information and back again.
Graphics card - This translates image data from
the computer into a format that can be displayed
by the monitor.
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Parallel Port
Serial Ports
USB Ports
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SERIAL PORT Considered to be one of the most
basic external connections to a computer, the
serial port has been an integral part of most
computers for more than 20 years. Although many
of the newer systems have done away with the
serial port completely in favor of USB
connections, most modems still use the serial
port, as do some printers, PDAs and digital
cameras. Few computers have more than two serial
ports.
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Parallel Ports

• If you have a printer connected to your computer,
  there is a good chance that it uses the parallel
  port. While USB is becoming increasingly popular,
  the parallel port is still a commonly used
  interface for printers. Parallel ports can be
  used to connect a host of popular computer
  peripherals
• Printers
• Scanners
• CD burners
• External hard drives
• Iomega Zip removable drives
• Network adapters
• Tape backup drives

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Universal Serial Bus (USB) Ports
The goal of USB is to end all of these headaches.
The Universal Serial Bus gives you a single,
standardized, easy-to-use way to connect up to
127 devices to a computer. Just about every
peripheral made now comes in a USB version. A
sample list of USB devices that you can buy today
includes Printers Scanners Mice Joysticks
Flight yokes Digital cameras Webcams
Scientific data acquisition devices Modems
Speakers Telephones Video phones Storage
devices such as Zip drives Network connections
Connecting a USB device to a computer is simple
-- you find the USB connector on the back of your
machine and plug the USB connector into it.
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A typical "B" connection
The rectangular socket is a typical USB socket on
the back of a PC.
A typical USB connector, called an "A" connection
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Input and output devices

• Input devices
• - Keyboard
• - mouse
• - barcode readers
• - Scanners
• Output devices
• - printer
• - plotter
• - VDU
• Can you name some others?