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

KeyboardAudioMouse

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

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

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 (1981-1984) 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 (1990-1993) communications standard between computer components

• Speed: up to 133 MB s-1

• 32-bit parallel connection

• ‘Plug and play’ – no set-up needed

Motherboard with PCI and ISA slotsfrom http://www.ibase-i.com.tw/mb700pixel600.jpg

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)CHfrom http://www.3dnews.ru/motherboard/intel-ht-chipset/

Motherboard with MCH and ICHfrom http://www.tomshardware.com/motherboard/20040712/i865-i875-mobos-21.html

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 ICHfrom http://www.tomshardware.com/motherboard/20040712/i865-i875-mobos-21.html

ICH

MCH

Socket for processor

Slots for RAM cards

AGP slot

Motherboardfrom http://www.techiwarehouse.com/cms/articles.php?cat=13

Motherboard connectorsfrom http://www.techiwarehouse.com/cms/articles.php?cat=13

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 boardfrom http://www.answers.com/topic/motherboard

End