1 Introduction to Computers Day 6

2 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.

3 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

4 Integrated Circuit An integrated circuit (IC) is a small chunk of silicon semiconductor material that contains hundreds of thousands to millions of electronic circuits.

5 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

6 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.

7 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

8 RAM Chips RAM is of the four following types. –Conventional memory –Upper memory –Extended memory –Expanded memory

9 Conventional Memory Consists of the first 640 kilobytes of RAM This area is used for running the operating system and applications programs.

10 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.

11 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.

12 Upper memory Conventional memory Extended memory 64MB 1MB 640KB 0 Types of RAM Expanded memory

13 Expanded Memory Lets 8088-chip-based PCs access memory over the limit of 640KB conventional memory. Used with ‘386SX’ or higher chips.

14 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.

15 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.

16 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)

17 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.

18 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.

19 Ports Ports commonly connect the main circuit board to the following –Keyboard –Monitor –Printer –Mouse –External modem –Joystick

20 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

21 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.

22 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.

23 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.

24 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

25 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

26 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

27 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

28 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

29 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