COMP 1017: Digital Technologies Session 7: Motherboards

What is a motherboard? The main PCB within a PC –or within another computer Contains all the essential components –and connectors for extras

What are the essentials (input)? Connectors and drivers for –Keyboard –Mouse Multi-purpose connectors for other input devices

What are the essentials (processing)? CPU Memory –But not storage Multi-purpose connectors for storage devices

What are the essentials (output)? Connector for screen output controller –Usually needs a separate circuit board Multi-purpose connectors for other output devices

Speed of computer components Very variable Fast components can waste time waiting for slower components Direct communication not normally possible between components of very different speeds

I/O devices sorted by bandwidth 10 B/s 100 B/s 1kB/s 10 kB/s 100 kB/s 1 MB/s 10 MB/s 100 MB/s Keyboard AudioMouse Joystick Scanner IDE HDD VDU TV Camera CD Rom

Slow devices Keyboard Mouse Joystick Audio

Fast devices VDU Hard drive CD-ROM Scanner

Even faster devices Processor Memory (RAM and cache) Graphics processors

Layout of component connections Extremely fast components talking directly to each other Fast components talking directly to each other Slow components talking directly to each other Connection North Bridge South Bridge

Buffers Areas of memory/storage where communications are stored before forwarding Message from slow device received and stored in buffer –Then sent quickly to fast device Message from fast devices stored –And then sent slowly to slow device

Resulting arrangement Pentium III 440 North Bridge South Bridge Main Memory Cache IDE DIsk Modem MouseKBd USB Printer SCSI Sound PCI Bus ISA Bus Organizing components by their speeds Incredibly Fast Very Fast Fast Slow Graphics

Bus Communications link between computer components Only one device can send a message at any one time –Others have to wait Can be parallel –several wires –so several bits can be transmitted simultaneously Or serial –One wire (cheaper) –But only one bit at a time (slower)

ISA bus ISA = Industry Standard Association Early ( ) communications standard between computer components Speed: up to 16 MB s -1 8 or 16-bit parallel connections

PCI bus PCI = Peripheral Component Interconnect Later ( ) communications standard between computer components Speed: up to 133 MB s bit parallel connection ‘Plug and play’ – no set-up needed

Motherboard with PCI and ISA slots from ISA slot PCI slot

More modern arrangement Idea copied from networking Hub connecting components of similar speed –Hub at centre; components at ends of ‘spokes’ Hubs communicate with each other

Hubs MCH = Memory Control Hub Connects very fast devices together in a ‘star’ configuration I(O)CH = Input-output Control Hub Connects together slower devices, also in a star configuration The two hubs communicate with each other

MCH and I(O)CH from

Motherboard with MCH and ICH from MCH ICH

Why are the components arranged this way? Longer wires mean more time to send messages –also means degradation of message at high speed Important for fast components to be close together Not so vital for slower components

Motherboard with MCH and ICH from ICH MCH Socket for processor Slots for RAM cards AGP slot

Motherboard from

Motherboard connectors from

Connectors Parallel port: usually for printers Serial port: old printers PS/2 connectors: ‘traditional’ mouse and keyboard connections VGA port: VDU output RJ-45 connector: Network connection

USB USB = Universal Serial Bus 480 Mb per second (USB 2.0) No need for masses of parallel connections Can be used for most peripherals Other similar standards available, e.g. Firewire, SCSI

Daughter boards Add-in boards that plug into slots on the motherboard e.g. ISA, PCI, AGP, memory,… Often have their own external connections through the back panel

Motherboard with expansion board from

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