9/28: Buses & Communication

• Buses: highways of the motherboard– system buses– local buses: PCI, ISA, EISA– expansion slots

• plug & play

• laptops: PCMCIA cards

• Ports: communicating with peripherals• serial ports

• parallel ports

• SCSI ports

• USB & Firewire

Buses: highways of the motherboard

• Alternative to wiring everything individually

• Function like a highway

• Buses are made of traces, microchips, and expansion slots.

• Components share them

• Different types:– system buses– local buses: PCI, ISA,

EISA

image courtesy of TigerDirect

Traces• Traces work like

the wires in cables: the circuits are used for: – power– data transmission– control commands– & addresses,

which are unique numbers assigned to each component on a bus. A component will ignore commands and data on the bus if another address is signaled.

image courtesy of How Computers Work

Microchips in Buses

• Microchips are used in some buses to increase the capacity of the bus in speed, in the number of components, and to relieve the load on the CPU.

image courtesy of How Computers Work

Expansion Slots

• Expansion slots are an easy way to expand and alter the computer’s setup.

• Plug & play: (PnP) a design that allows installation of adapter cards with reduced difficulty.

image courtesy of How Computers Work

System Buses

• Connect the CPU to other components.

• Buses, like everything else in computers, have grown: current standard is 32-bit.

• Contain address lines, command lines and data lines– address lines tell what component is involved.– command lines carry commands for the component.– data lines carry the actual data for/from the

component.

Local Buses

• The hubs of the local buses manage the connections and transfers of data, relieving load on CPU.

• ISA - Industry Standard Architecture: 8-bit and 16-bit, original one

• EISA - Extended ISA: 32 bit, better

• PCI - Peripheral Component Interconnect: 32 bit, operate at higher speeds (MHz), better yet.

• AGP – Advanced Graphics Port

Laptops: PCMCIA Cards

• PCMCIA cards function in a laptop like expansion cards function in a desktop

• No room in a laptop for physical expansion

• Networking, modems, etc. can be added to a laptop by using these cards.

images courtesy of Toshiba, & Belkin

Ports: not quite buses

• For communicating with peripherals– printers, external modems, keyboards, scanners, etc.

• Major varieties:– serial– parallel– SCSI– USB– Firewire

Serial ports

• Four wires total:– One wire to transmit data, – One wire to accept data,– Two wires for electrical grounding.

• Common uses:– modems– mice

Parallel ports

• Nine or Twenty-Five wires total:– Eight wires to transmit data, – Other wires for electrical grounding,– Some wires for commands & communication.

• Common uses:– printers– scanners

SCSI ports

• Advantages: many– much faster than serial or parallel ports– provides ability to daisy-chain peripherals

• Disadvantages: few– expensive– uncommon

• Common uses:– printers– external drives (hard disk, tape, CD-ROM, etc.)

USB (Universal Serial Bus) ports

• Four wires total:– One wire to transmit data, – One wire to accept data,– Two wires for electrical power.

• Common uses: any peripheral – mice -scanners– external modems - joysticks – keyboards - printers

images courtesy of www.allUSB.com

• aka IEEE 1394

• Developed by Apple

• Will probably replace USB someday

• Daisy-chaining, faster

• Common uses: any peripheral – mice -scanners– external modems - joysticks – keyboards - printers

images courtesy of Apple and firewirestuff.com

Firewire ports