Buses

1
Buses

• ISA bus
• 8-bit industry standard architecture bus used on
  the original 8088 PC
• Later revised to have a 16-bit path
• Micro channel architecture (MCA) bus
• A proprietary IBM PS/2 bus, seldom seen today,
  with a width of 13 or 32 bits and multiple master
  control, which allowed for multitaskiing
• EISA (extended ISA) bus
• 32-bit bus that can transfer 4 bytes at a time at
  a speed of about 20 MHz

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Buses

• Universal serial bus (USB)
• Designed to make installation and configuration
  of I/O devices easy, providing room for as many
  as 127 devices daisy-chained together
• Uses only a single set of resources for all
  devices on the bus
• Expected to eventually replace serial and
  parallel ports
• Windows NT does not support it, but Windows 95
  with the USB update, Windows 98, and Windows 2000
  do

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USB Ports
4
FireWire or i.Link or 1394

• An expansion bus that can also be configured to
  work as a local bus
• Similar in design to USB, using serial
  transmission of data, but faster
• Supports data speeds as high as 1.2 Gbps
• Viable option for connecting network cards,
  camcorders, DVD, and other high-speed,
  high-volume devices

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FireWire or i.Link or 1394

• Likely to replace SCSI, providing an easy method
  to install and configure fast I/O devices
• Must be supported by the operating system
• IEEE 1394.3
• New standard developed by the 1394 Trade
  Association
• Designed for peer-to-peer data transmission

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Local I/O Buses

• A local bus that provides I/O devices with fast
  access to the CPU
• Must connect to the CPU by way of the memory bus

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Example of a Proprietary Local Bus
8
VESA (Video Electronics Standards Association) VL
Bus

• Used on 80486 computers for connecting 32-bit
  adapters directly the the local processor bus
• Has been replaced with the PCI (peripheral
  component interconnect) bus

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VESA Local Bus Expansion Slot
10
PCI Bus

• Now the standard local I/O bus not only with
  Pentium CPUs but also with RISC CPUs
• Has a 32-bit data path and runs at 33 MHz when
  the system board runs at 66 MHz
• Advantage
• Devices connected to it can run at one speed
  while the CPU runs at a different speed
• Interfaces with the expansion bus and the memory
  bus, serving as the go-between for the two,
  controlling the input and output to the expansion
  bus

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PCI Bus Expansion Slots
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The PCI Bridge
14
Accelerated Graphics Port

• A slot on a system board for a video card that
  provides transfer of video data from the CPU that
  is synchronized with the memory bus
• Does not allow for expandability can only
  support a single card
• Runs at same speed as the memory bus, connects
  directly to it, and has a 32-bit-wide data path

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Accelerated Graphics Port

• Most powerful feature DIME (direct memory
  execute)
• To work at full potential, system board must run
  at minimum of 100 MHz

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Accelerated Graphics Port
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Audio Modem Riser (AMR)

• A slot on some newer system boards that can
  accommodate a small modem card or sound card
• Makes it possible to add the card at a low cost
  without using up a PCI or ISA slot

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Setting the CPU and Bus Speeds

• Change the speed of the memory bus
• Whatever the memory bus speed is, the PCI bus
  speed is half or one third of that
• Change the multiplier that determines the speed
  of the CPU
• The choices are normally 1.5, 2, 2.5, 3, 3.5, and
  so forth

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System Board Speeds
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Setting Speeds Using Jumpers
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On-Board Ports

• Ports that are directly on the system board, such
  as a built-in keyboard port or on-board serial
  port
• When buying a new computer or system board, look
  for the ability to disable ports, floppy drive
  connectors, or hard drive connectors coming
  directly from the system board by changing the
  hardware configuration

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On-Board Ports
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Hardware Configuration

• Communicates to the CPU what hardware components
  are present in the system and how they are set up
  to interface with the CPU
• Provided on system board in three ways
• DIP switches
• Jumpers
• CMOS

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Setup Stored on a CMOS Chip

• Retains data even when computer is turned off

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Setup Stored on a CMOS Chip
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Chapter Summary

• System board
• Central site of computer logic circuitry
• Location of the most important microchip in the
  computer, the CPU