Bus Architecture

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Bus Architecture
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What is a bus?

• In computer architecture, a bus is a subsystem
  that transfers data or power between computer
  components inside a computer or between
  computers. Unlike a point-to-point connection, a
  bus can logically connect several peripherals
  over the same set of wires. Each bus defines its
  set of connectors to physically plug devices,
  cards or cables together.

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Industry Standard Architecture (ISA)

• ISA originated as an 8-bit system in the IBM PC
  in 1981, and in 1984 a 16-bit version was
  introduced.
• Bus speed 8.33Mhz
• PnP support Original version none, Later version
  offered poor PnP support.

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ISA Expansion Slots
8-bit slot
16-bit slot
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Micro Channel Architecture (MCA)

• 16-bit bus which operates at 10Mhz which was
  introduced by IBM in its PS2 systems.
• First bus to be software configurable.
• Incompatible with ISA cards.
• Proprietary architecture.

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Peripheral Component Interconnect (PCI)

• 32-bit PnP bus capable of operating as a 64-bit
  bus.
• Bus Speed 33 or 66Mhz
• By far the most widely used in modern computers.
• Permits IRQ sharing.

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PCI Express (PCIe)

• PCI Express is a serial connection that
  operates more like a network than a bus. Instead
  of one bus that handles data from multiple
  sources, PCIe has a switch that controls several
  point-to-point serial connections.

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PCIe Architecture and Connectors
Smaller PCIe cards will fit into larger PCIe
slots. The computer simply ignores the extra
connections. For example, a x4 card can plug into
a x16 slot. A x16 card, however, would be too big
for a x4 slot.
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PCIe Motherboard Connectors
PCI Express slots (from top to bottom x4, x16,
x1 and x16)
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Accelerated Graphics Port (AGP)

• The Accelerated Graphics Port (also called
  Advanced Graphics Port) is a high-speed
  point-to-point channel for attaching a graphics
  card to a computer's motherboard, primarily to
  assist in the acceleration of 3D computer
  graphics. Some motherboards have been built with
  multiple independent AGP slots. AGP is slowly
  being phased out in favour of PCI Express.

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Available Versions

• AGP 1x, using a 32-bit channel operating at 66
  MHz resulting in a maximum data rate of 266
  megabytes per second (MB/s) 3.3 V signaling.
• AGP 2x, using a 32-bit channel operating at 66
  MHz double pumped to an effective 133 MHz
  resulting in a maximum data rate of 533 MB/s
  signaling voltages the same as AGP 1x.
• AGP 4x, using a 32-bit channel operating at 66
  MHz quad pumped to an effective 266 MHz resulting
  in a maximum data rate of 1066 MB/s (1 GB/s) 1.5
  V signaling.
• AGP 8x, using a 32-bit channel operating at
  66 MHz, strobing eight times per clock,
  delivering an effective 533 MHz resulting in a
  maximum data rate of 2133 MB/s (2 GB/s) 0.8 V
  signaling.

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Compatibility

• AGP cards are backwards and forwards compatible
  within limits. 1.5 V cards will not go into 3.3 V
  slots and vice versa, though "Universal" slots
  exist which accept either type of card. AGP Pro
  cards (rarely used) will not fit into standard
  slots, but standard AGP cards will work in a Pro
  slot.

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Universal Serial Bus (USB)

• A serial standard for connecting devices.
• Up to 127 devices can be connected to the USB
  bus.
• USB current standard is USB 2.0 which supports a
  transfer rate of 480Mbps.

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USB Connectors and Hubs
USB A and B female connector
USB Hub
USB male A connector