Download - COMP 1017: Digital Technologies
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