PowerRAC Chassis 320 — 3U Rackmount for UP2000 Series Motherboards

The PowerRAC Chassis 320 was a 3U rackmount enclosure that Alpha Processor, Inc. designed specifically for its dual-processor UP2000 series motherboards. It combined heavy steel construction, redundant cooling, full-length PCI support and a roughly 600 W power supply to make dense Alpha clusters, render farms and ISP servers practical.

Why a custom chassis

API's entire strategy relied on the PC ecosystem. The single-processor UP1000 was a standard ATX board that dropped into any off-the-shelf tower. The UP2000 was a different story. Its Tsunami-class chipset is a multi-chip design, with separate control, data-path and PCI interface parts, and the board needed extra area for them and for its wide memory banks. The result was an oversized board that did not fit comfortably in generic PC cases, and two Alpha 21264 modules produced far more heat than a typical desktop processor.

Integrators could build their own enclosures, but many of API's target customers, particularly universities, studios and service providers, wanted a validated package. The PowerRAC Chassis 320 filled that gap: a rackmount case engineered around the UP2000's mounting pattern, power draw and airflow needs.

Design and construction

The chassis follows the conventions of late-1990s server hardware. It is built from heavy-gauge steel rather than thin sheet metal, which gives rigidity when the unit is racked, reduces vibration and helps with electromagnetic shielding. In a rack full of loaded nodes that stiffness mattered: a flexing chassis could stress the board, loosen connectors and make servicing difficult.

Cooling

Cooling was the central engineering challenge. A pair of Alpha processors, their backside cache SRAMs and a full set of PCI cards generate a large amount of heat in a small space. The PowerRAC 320 uses multiple fans arranged for front-to-back airflow, with redundancy so that the failure of a single fan does not immediately put the processors at risk. Front-to-back flow also suited standard data centre layouts with cold and hot aisles.

Expansion and storage

The 3U height was chosen deliberately. It is tall enough to accept full-length, full-height PCI cards standing upright, so there was no need for riser cards or low-profile adapters. That meant customers could fit high-end SCSI and RAID controllers, cluster interconnect cards and multi-port network adapters. Front-accessible drive bays provided room for hard disks and removable media such as CD-ROM or tape.

Main characteristics

The roughly 600 W supply left headroom above the needs of two processors, several gigabytes of memory, a stack of drives and fully populated PCI slots. Mounting rails were included so units could slide in and out of a standard rack for service without being unbolted and lifted.

Target workloads

The PowerRAC 320 was aimed at buyers who needed many Alpha nodes in limited space:

• Linux compute clusters — dense Beowulf-style installations in universities and research labs, where a rack of dual-Alpha nodes could deliver very high floating-point throughput.
• Render farms — film, animation and visualisation studios running CPU-heavy renderers around the clock.
• ISPs and hosting providers — 64-bit web, mail and database servers in colocation racks where floor space was billed by the unit.
• Technical servers — simulation and engineering servers that needed large memory and plenty of I/O.

In a standard 42U rack, a 3U chassis allows over a dozen dual-processor nodes, with room left for switches and power distribution. For its time that was a reasonably dense Alpha installation, well ahead of racking pedestal workstations.

Deployment considerations

Density brought its own problems. A full rack of dual-Alpha nodes drew a substantial amount of power and rejected a matching amount of heat, so sites had to plan circuits and air conditioning carefully. The redundant fan arrangement helped keep individual nodes running, but cluster operators still monitored temperatures closely, because a hot spot at the top of a rack could push processors toward their thermal limits. Cable management was another practical concern: each node typically needed power, one or two network connections, a cluster interconnect cable and often a serial console line, and the rear of a fully populated rack could quickly become crowded.

The one-year warranty was typical for merchant-market server hardware of the period. Integrators who resold complete systems often layered their own service contracts on top, handling spares and on-site replacement for customers who could not tolerate long outages.

Operating system and software support

The chassis itself is operating-system neutral; software support is determined by the UP2000 board inside it. In practice most PowerRAC 320 systems ran Linux, using the Alpha ports of Red Hat, SuSE or Debian and Compaq's optimising compilers for scientific work. Tru64 UNIX was validated primarily on Compaq's own hardware, so it was not a mainstream choice in API enclosures, and Windows NT for Alpha had already been cancelled by the time these systems shipped.

Positioning within the API product line

The PowerRAC 320 completed the UP2000 package: board, processor modules and enclosure from a single vendor. It was API's answer to rackmount AlphaServers, offering comparable node density at lower cost with more freedom over components. The idea of dense, rack-optimised Alpha servers continued in API NetWorks' later CS20, a 1U dual-processor system. For support information see the support pages.