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The CS20 is a 1U dual processor 21264 server designed by Alpha Processor, Inc., later API NetWorks, and the DS20L is Compaq's version of it. Apart from the front cover, the two differ only in their SRM firmware and the SCSI controller on the PCI riser card. ¹⁾

Except where noted, the following comes from API's specification for the CS20. ²⁾

• Two 667 MHz 21264A or 833 MHz 21264B CPUs with 4 MiB of DDR L2 cache each
• Two 64-bit 33 MHz PCI slots
• Onboard Ultra3 SCSI (Symbios 53c1000)
• 1U rackmount
• Up to 2 GiB of memory in eight DIMM slots on the DS20L ³⁾
• Two independent PCI buses, with most onboard devices on bus 0, so demanding cards perform better on the second bus ⁴⁾

Use the final SRM version, V6.6-10 on the DS20L (see final SRM versions).

If the DS20L environment variable sysvar is set to 5, it must be set to 12 and the console re-initialized before the firmware update utility is run, then reset to 5 and re-initialized after the update. ⁵⁾

Current kernels support the Shark (CONFIG_ALPHA_SHARK, or a generic kernel), which boots from SRM with aboot. ⁶⁾ See also Tsunami Systems.

The two onboard Ethernet controllers are Intel 82559s, one on each host PCI bus; ⁷⁾ they use the e100 driver. ⁸⁾ The DS20L's console lists its onboard Ultra3 SCSI controller as an Adaptec 29160, ⁹⁾ which uses the aic7xxx driver. ¹⁰⁾

The SRM console is used through the COM1 or COM2 serial port, at 9600 baud by default, ¹¹⁾ and in racks these ports are usually reached through terminal servers. ¹²⁾ To have Linux use the serial console as well, see Using SRM.

• Power supplies: the DS20L and CS20 power supplies are prone to failure, which shows as the front LED changing from flashing green to steady red. ^{13) 14)} On one DS20L the replacement capacitors failed as well. ¹⁵⁾
• Noise: the systems are loud. ¹⁶⁾ The DS20L is rated at a sound power level of 6.7 B, 51 dBA for bystanders, idle or operating. ¹⁷⁾
• Power: a DS20L typically draws 275 W. ¹⁸⁾