ClearPath Dorado 300/400/700/800/4000/4100 Server I/O Planning ...

PCI-Based I/O Hardware
• ASIC
An ASIC is a custom-designed chip for a specific application. ASICs improve
performance over general-purpose CPUs because ASICs are hardwired to do a
specific job and do not incur the overhead of fetching and interpreting stored
instructions.
• Signaling
The original standard, supported by the technologies of that time, was based on
5.0-volt signaling for the cards and the backplane. As the technology evolved,
3.3-volt signaling became a better choice. However, vendors offered backplanes
that had all the slots supporting either 3.3-volt or 5.0-volt PCI cards. This meant the
PCI cards could not be mixed within the same backplane. Then, PCI add-in card
vendors developed Universal cards that can plug into a 3.3-volt slot or a 5.0-volt
slot.
• PCI Revisions
− Revision 2.1
Supported 3.3-volt cards, 5.0-volt cards, and Universal cards.
− Revision 2.2
Minor changes.
− Revision 2.3
Supported 3.3-volt cards and Universal add-in cards; no support for 5.0-volt
cards.
1.2.2. I/O Bus Layout
The following figure shows the key components of the I/O complex and the primary
and secondary PCI buses that connect them.
The SIOH and P64 are Intel chips used for I/O processing. There is no further
description in this document.
The DVD Interface Card and the PCI Host Bridge Card are specific HBAs. They are
described later in this section.
The expansion rack contains up to seven additional HBAs or NICs. It is described later
in this section.
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