System Bus

System Bus

1. Bus Interconnection

   • Data bus
     • Data lines that provide a path for moving data among system modules
     • The width of data bus is the key factor in determining the overall system performance
     • May consists of 36, 64, 128, or more seperate lines
   • Address Bus
     • Width determines the maximum possibles memory capacity of the system
     • also used to address I/O ports
   • Control Bus
     • -Command signal specify operations to be performed
     • Used to control the access and the use of data and address information
     • Control signal transmit both commands and timing informations among modules

2. Bus Hierachy

   • The standard I/O Bus
     • Used for slower peripherals (modems) and also compatibility with older devices
     • The industry Standard Architecture (ISA) bus
   • The local i/o bus (High Speed I/O Bus)
     • High speed i/o bus used for connecting performance critical peripherals to the memory ,chipset, and processor
     • EX: Video cards
     • Two most common local i/o buses are the VLB and PCI

3. Characteristic Of Bus

   • Bus Bandwidth
     • Measured in bits per second
     • Bandwidth=Bus Width * Bus Speed
     • For very slow bus,bandwidth=1/2 (Bus width*Bus Speed)

4. PCI and PCI Express

   • A popular high bandwidth , processor independent bus that can function as a mezzanine or peripehal bus
   • Delivers better systems performances for high speed I/O susbsystems
   • PCI Special Interest Group(SIG)-created to develop further and maintain the compatibility of the PCI specification

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