Group Approves New PCI Bus That Doubles Throughput
Windows Magazine - July 1999
Servers and high-powered workstations are about to get a big
bandwidth boost. The PCI Special Interest Group (SIG), which
manages the PCI specification, has approved a new PCI bus that
doubles throughput. IBM, Hewlett-Packard and Compaq-normally
competitors in the PC server market-developed the new bus,
dubbed PCI-X, last year.
The faster bus was designed for high-speed I/O devices, such as
Gigabit Ethernet cards, Ultra3 SCSI and Fibre Channel. The three
companies turned the specification over to the PCI SIG Steering
Committee for review last September, which approved the new
technology with almost no changes. The next step is member
review, where PCI SIG members can request technical changes to
the specification.
PCI-X is not likely to be found in cheaper, low-end machines for
some time, since it adds to the cost of the motherboard. Currently,
PCI supports one 64-bit bus running at 66MHz, while the rest run
at 32 bits or 64 bits at 33MHz. Maximum throughput for a system
is 532MBps. PCI-X doubles all of that, cranking up one bus to
133MHz at 64 bits and the rest of the buses to 66MHz at 64 bits for
a maximum throughput of 1.06GBps. It will initially be used in
servers and workstations, since they need all the throughput they
can get.
To receive the benefit of the high-speed bus, vendors will have to
create their own PCI-X cards that run at the higher speed. Adaptec,
3Com and LSI Logic have all signed on to support
the new bus. Both PCI and PCI-X buses and cards will be backward
compatible, according to Richard Baek, executive director of the SIG.
A PCI card will work in a PCI-X slot, and any PCI-X card placed in a
standard PCI slot will automatically step down its speed to run at 33MHz.
The SIG expects its membership to approve the spec by the third
quarter and for products to begin appearing six to nine months after
that. Expect a number of PCI-X-based systems to be announced at
Comdex in November, according to Baek.
The PCI SIG also approved Mini PCI, a variation of the PCI bus
for communication peripherals used in mobile products, such as
laptops and handheld devices. The Mini PCI spec is out for
member review, with approval expected some time this quarter.
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