Hardware Reference
In-Depth Information
boards. Peripherals, such as SCSI adapters, network cards, video cards, and more, can
be plugged into PCI bus slots. PCI Express is a faster development of the PCI bus.
•
ISAbus
—Thisisan8MHz16-bitbusthathasdisappearedfrommodernsystemsafter
appearingintheoriginalPCin8-bit,5MHzformandinthe1984IBMATinfull16-bit
8MHz form. It is a slow-speed bus, but it was ideal for certain slow-speed or older
peripherals. It has been used in the past for plug-in modems, sound cards, and various
other low-speed peripherals. The ISA bus is created by the South Bridge part of the
motherboard chipset, which acts as the ISA bus controller and the interface between
theISAbusandthefasterPCIbusaboveit.TheSuperI/Ochipusuallywasconnected
to the ISA bus on systems that included ISA slots.
Some older motherboards feature a special connector called an
Audio Modem Riser
(AMR) or a
Communications and Networking Riser
(CNR). These are dedicated connect-
ors for cards that are specific to the motherboard design to offer communications and
networking options. They are
not
designed to be general-purpose bus interfaces, and few
cards for these connectors are offered on the open market. Usually, they're offered only
as an option with a given motherboard. They are designed such that a motherboard manu-
facturer can easily offer its boards in versions with and without communications options,
without having to reserve space on the board for optional chips. Normal network and mo-
dem options offered publicly, for the most part, are still PCI based because the AMR/
CNR connection is somewhat motherboard specific.
Figure 4.38
compares these connect-
ors. Current motherboards have largely abandoned AMR and CNR slots.
Figure 4.38
The AMR slot (top left) and CNR slot (top center) compared to PCI slots. When the AMR slot
is used, the PCI slot paired with it cannot be used.
