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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– 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– 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– DRAM (Dynamic RAM) commonly used– SRAM (Static RAM) for specialised use

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RAM Chips

• RAM is of the four following types.– 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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Upper memory

Conventional memory

Extended memory

64MB

1MB

640KB

0

Types of RAM

Expandedmemory

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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

– PROM (Programmable ROM)blank chips on which the buyer, using special

equipment writes the program. Once the program is written it cannot be erased.

– EPROM (Erasable PROM)like PROM chips, but new material can be

written.Erasing needs the use of UV rays.

– 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– Cache memory– Video memory (Video RAM)– Flash memory (flash RAM)

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Other forms of Memory

• Cache memorya 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– 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– 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 9-pin 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, magnetic-tape 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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• Memory Expansion cards (SIMMs)

• Expansion cards are used to connect the following devices to the main circuit board

– 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

Expansion Cards

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• 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.

Bus Lines

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• Principal PC bus standards (architectures)– Industry Standard Architecture (ISA)– Micro Channel Architecture (MCA)– Enhanced ISA (EISA)– PCI (Peripheral Computer Interface)

– Personal Computer Memory Card International Association (PCMCIA)

Bus Lines

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• 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.

Bus Lines

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• 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.

Bus Lines

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• 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

Local Bus Extensions