Transcript File

Introduction to Computers
Day 6
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Main Circuit Board of a PC
• The main circuit board (motherboard or
system board) is the central nervous system
of the computer. All the important
components are either mounted on it or
connected to it.
• Primary electronic circuitry resides in it.
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Main Circuit Board of a PC
• Consists of
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RAM slots
- ROM chips
CPU
- Clock chip
BIOS chip
- Expansion slots
Disk drive controller chip
Connectors for disk drives
Keyboard connectors
Connectors for serial and parallel ports
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Integrated Circuit
• An integrated circuit (IC) is a small chunk of
silicon semiconductor material that contains
hundreds of thousands to millions of
electronic circuits.
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Chips
• Integrated circuit chips are used in several
different ways
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CPU (microprocessor)
ROM chips
RAM (SIMMs)
Video display controller chip
Disk drive controller chip
Coprocessor chip
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RAM Chips
• Random Access Memory (RAM, main
memory, primary storage) is memory that
temporarily holds data and instructions that
will be needed shortly by the CPU.
• Data are stored and retrieved at random
from anywhere in the electronic RAM chip,
in approximately equal amounts of time, no
matter what the specific data locations are.
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RAM Chips
• RAM chips are often mounted on a small
circuit board, such as Single Inline Memory
Module (SIMM) which is plugged into the
motherboard.
• Two principal types of RAM chips are
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DRAM (Dynamic RAM) commonly used
SRAM (Static RAM) for specialised use
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RAM Chips
• RAM is of the four following types.
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Conventional memory
Upper memory
Extended memory
Expanded memory
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Conventional Memory
• Consists of the first 640 kilobytes of RAM
• This area is used for running the operating
system and applications programs.
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Upper Memory
• Memory located between 640 KB and 1MB
of RAM (384 KB).
• Microcomputers with ‘286’ or higher chips
use this area for storing parts of the
operating system, leaving conventional
memory available for running application
programs.
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Extended Memory
• All memory over 1MB. Used by ‘286’ or
higher chips.
• Not all programs can use extended memory.
Indeed, DOS and DOS programs can’t
access it. Programs to be able to use this,
they must being written with DOS
extenders.
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Types of RAM
64MB
Extended memory
1MB
Upper memory
640KB
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Expanded
memory
Conventional
memory
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Expanded Memory
• Lets 8088-chip-based PCs access memory
over the limit of 640KB conventional
memory.
• Used with ‘386SX’ or higher chips.
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ROM Chips
• Read-Only Memory (ROM, firmware)
cannot be written on or erased by the
computer user.
• Contain programs that are built in at the
factory.
• There are instructions for basic computer
operations, such as those that start the
computer or put the characters on the screen.
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ROM Chips
• Three variants of ROM chips
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PROM (Programmable ROM)
blank chips on which the buyer, using special
equipment writes the program. Once the program
is written it cannot be erased.
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EPROM (Erasable PROM)
like PROM chips, but new material can be
written.Erasing needs the use of UV rays.
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EEPROM (Electrically EPROM)
can be reprogrammed using special electrical
impulses. Need not be removed from the computer
in order to be changed.
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Other forms of Memory
• Performance of microcomputers can be
enhanced further by adding other forms of
memory
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Cache memory
Video memory (Video RAM)
Flash memory (flash RAM)
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Other forms of Memory
• Cache memory
a special high-speed memory area that the CPU
can access quickly
• Video memory (Video RAM)
are used to store display images for the monitor.
• Flash memory (flash RAM)
Card consists of circuitry on credit-card size cards
that can be inserted into slots connecting to
the motherboard. Is non-volatile. Used in
notebooks.
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Ports
• A port (interface) is a connection from the
main circuit board to a peripheral device.
The peripheral is connected to the port by a
special cable.
• Ports are arranged along the rear of the main
circuit board and provide connections
through the back of the system of the system
unit.
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Ports
• Ports commonly connect the main circuit
board to the following
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Keyboard
Monitor
Printer
Mouse
External modem
Joystick
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Ports
• A port is a socket on the outside of the
system unit that is connected to an
expansion board or the main board on the
inside of the system.
• Common types of ports
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Parallel ports
Serial ports
Video adapter ports
SCSI ports
Game ports
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• Parallel port
– Allows lines to be connected that will enable 8
bits to be transmitted simultaneously (printer).
• Serial port (RS-232 port, COM)
– Enables a line to be connected that will send
bits one after the other on a single line
(modem, mice, keyboard).
• Video adapter ports
– Used to connect the video display monitor
outside the computer to the video adapter card
inside the system unit. Monitors may have 9pin plug or 15-pin plus.
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• SCSI ports
– Small Computer System Interface (SCSI)
provides an interface for transferring data at
high speed for up to eight SCSI-compatible
devices (external hard-disk drives, magnetictape backup units, CD-ROM drives, Scanners).
• Games ports
– Allows you to attach a joystick or similar
game-playing device to the system unit.
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Expansion Slots
• Expansion card (adapter card) is a printed
circuit card with circuitry that gives the
computer additional capabilities. This is
inserted into an expansion slot on the main
board.
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Expansion Cards
• Memory Expansion cards (SIMMs)
• Expansion cards are used to connect the following
devices to the main circuit board
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Video monitor (Display adapter, graphics display cards)
Dirk drive (controller cards)
Scanner (controller cards)
External CD-ROM (controller cards)
Internal modem
- Sound
TV tuner
- Network
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Bus Lines
• A bus line (bus) is an electrical pathway
through which bits are transmitted within the
CPU and between the CPU and other units in
the system unit.
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Bus Lines
• Principal PC bus standards (architectures)
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Industry Standard Architecture (ISA)
Micro Channel Architecture (MCA)
Enhanced ISA (EISA)
PCI (Peripheral Computer Interface)
– Personal Computer Memory Card International
Association (PCMCIA)
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Bus Lines
• Industry Standard Architecture (ISA)
– First 8 bits, then 16 bits, is the most common PC
bus.
• Micro Channel Architecture (MCA)
– Used in IBM PS/2 line of microcomputers. 32 bits.
• Enhanced ISA (EISA)
– 32 bits. ISA cards will run in EISA slots.
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Bus Lines
• PCI
– The latest standard available in 32-bits and 64 bits
• Personal Computer Memory Card International
Association (PCMCIA)
– Completely open, nonproprietary bus standard for
notebooks, sub-notebooks and palmtops.
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Local Bus Extensions
• Used to bypass existing standards bus systems
(connect to peripheral computers directly to the
microprocessor).
– Peripheral Component Interconnect (PCI)
• 64-bit data path used in Pentium-based systems.
– Video Electronics Standard Association (VESA)
• 32 bits, used with ‘486 systems
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