Bus Architecture
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.
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.
ISA Expansion Slots
8-bit slot
16-bit slot
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.
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.
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.
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.
PCIe Motherboard Connectors
PCI Express slots (from top to bottom: x4,
x16, x1 and x16)
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.
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.
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.
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.
USB Connectors and Hubs
USB A and B
female
connector
USB Hub
USB male A
connector