PCI can connect more devices than VL-Bus, up to
five external components. Each of the five connectors for an external component
can be replaced with two fixed devices on the motherboard. Also, you can have
more than one PCI bus on the same computer, although this is rarely done. The
PCI bridge chip regulates the speed of the PCI bus independently of the CPU's
speed. This provides a higher degree of reliability and ensures that
PCI-hardware manufacturers know exactly what to design for.
PCI
originally operated at 33 MHz using a 32-bit-wide path. Revisions to the
standard include increasing the speed from 33 MHz to 66 MHz and doubling the
bit count to 64. Currently, PCI-X provides for 64-bit transfers at a speed of
133 MHz for an amazing 1-GBps (gigabyte per second) transfer rate!
PCI cards
use 47 pins to connect (49 pins for a mastering card, which can control
the PCI bus without CPU intervention). The PCI bus is able to work with so few
pins because of hardware multiplexing, which means that the device sends
more than one signal over a single pin. Also, PCI supports devices that use
either 5 volts or 3.3 volts.
|
Bus Type |
Bus Width |
Bus Speed |
MB/sec |
|
ISA |
16 bits |
8 MHz |
16 MBps |
|
EISA |
32 bits |
8 MHz |
32 MBps |
|
VL-bus |
32 bits |
25 MHz |
100 MBps |
|
VL-bus |
32 bits |
33 MHz |
132 MBps |
|
PCI |
32 bits |
33 MHz |
132 MBps |
|
PCI |
64 bits |
33 MHz |
264 MBps |
|
PCI |
64 bits |
66 MHz |
512 MBps |
|
PCI |
64 bits |
133 MHz |
1 GBps |