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PA-RISC Buses

EISA

The Extended ISA bus replaced the older ISA bus present in some HP Unix systems and thus inherited several details from it. EISA buses are available in several older series 700 systems, either onboard or through a seperate adaptor, which made it possible to use third-party, generic expansion cards.

For available expansion cards, see EISA expansion-cards.

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GSC/HSC

The General System Connect bus is the primary I/O bus on most of the older, numbered 700s workstations. It connects most of the I/O devices to the system bus. Some CPUs directly attach to GSC (PA-7100LC and PA-7300LC).

General features:

There are several variations of the GSC bus:

  1. Original GSC (GSC-1X) — peak data rate 142MB/s
  2. GSC+ (Extended GSC) — maximum frequency of 40MHz with peak data rates of 160MB/s (132MB/s with 33MHz, 144MB/s with 36MHz)
  3. GSC-1.5X provides additional extended write operations
  4. GSC-2x — peak data rate 256MB/s

Expansion cards for GSC were available in different formfactors (FFs):

For available expansion cards, see GSC expansion-cards.

References

PA-RISC Linux: Glossary
The PARISC-Linux Project (May 2005).
HP-UX Workstation HCL (Hardware Compatibility List) PA-RISC (pp. 188-189, 191, 198)
Hewlett-Packard Company (July 1998, 14th ed.).

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HP-PB

The HP-Precision Bus is the I/O bus in most older Series 800 servers. There are basically two formfactors: single and double (like 2U VME).

References

HP-UX Workstation HCL (Hardware Compatibility List) PA-RISC (p. 190)
Hewlett-Packard Company (July 1998, 14th ed.).

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PCI

With the PCI bus, HP tried to change its workstation designs to faciliate a standard expansion/device bus. This made it possible to use cheaper off-the-shelf products such as I/O chips and cards without having to to build (HP-proprietary) GSC/SGC interfaces.

There also were much more PCI expansion cards available than for instance HP GSC or SGC ones, driving the design costs of expansion cards down. Some of HP’s PCI expansion cards are relabeled 3rd party products or OEM designs which only were modified with an HP PA-RISC compatible firmware and supplied with an HP-UX driver.

Missing drivers is the limiting factor in using generic third-party PCI expansion cards in HP PA-RISC systems with HP-UX. In most cases HP supplied drivers only for their own (HP-branded) products. Using for example Adaptec SCSI cards or Intel network adapters is in most cases impossible since no proper HP-UX drivers exist for them.

With open source operating systems as Linux or OpenBSD it is more likely that a driver for the specific expansion card already exists and was/can be ported to the PA-RISC port.

PCI buses used in PA-RISC computers overview
PCI Clock Width Data rate
max		 Signalling
PCI-32/33 33MHz 32-bit 133MB/s 3.3V/5V
PCI-32/66 66MHz 32-bit 266MB/s 3.3V
PCI-64/33 33MHz 64-bit 266MB/s 3.3V/5V
PCI-64/66 66MHz 64-bit 533MB/s 3.3V
PCI-X 66MHz 64-bit 533MB/s ?
PCI-X 100MHz 64-bit 800MB/s 3.3V
PCI-X 133MHz 64-bit 1066MB/s ?

Any PCI card should run in any PCI slot if the voltage (3.3V or 5V) is correct. Slower cards in faster slots will reduce the overall PCI bandwidth of that particular bus.

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Runway

Runway is the system bus newer PA-RISC CPUs (PA-7200 and PA-8000 upwards) connect to. It is a synchronous, split-transaction bus.

References

A High-Performance, Low-Cost Multiprocessor Bus for Workstations and Midrange Servers
William R. Bryg, Kenneth K. Chan, and Nicholas S. Fiduccia (February 1996: Hewlett-Packard Journal).

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SGC

The System Graphics Connect bus is basically the mainbus of the older series 700 computers. Thus the SGC-expansion cards directly attach to the mainbus in these systems. There are also two different form-factors: EISA and DIO.

For available expansion cards, see expansion-cards.

References

HP-UX Workstation HCL (Hardware Compatibility List) PA-RISC (p. 195)
Hewlett-Packard Company (July 1998, 14th ed.).

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