The AlphaServer DS20 is a one- or two-processor 21264 server with its CPUs on daughtercards and two PCI buses. ¹⁾ It was built from the same design as the AlphaPC 264DP and sold as a pedestal that also fits M-series cabinets. ²⁾

Except where noted, the following comes from the Windows NT catalog. ³⁾

• One or two 500 MHz 21264 CPUs with 4 MiB of level 2 cache, on daughtercards
• 21272 (Tsunami) core logic with two PCI buses
• Five 64-bit PCI slots, one 64-bit PCI/ISA combination slot, and 16 DIMM slots
• Memory in kits of four industry-standard ECC DIMMs, up to four kits for 4 GiB; kits of 128 MiB, 256 MiB, 512 MiB, and 1 GiB
• Onboard diskette controller, two serial ports, one parallel port, keyboard and mouse controller; SCSI and Ethernet are PCI options
• Ten internal storage slots: floppy, CD-ROM, one further 5.25-inch removable media bay, and seven hot swap StorageWorks disks, up to 128 GB with 18.2 GB disks
• Hot swap disks, redundant power supplies, ECC memory, heat, fan, and power supply sensors
• The original DP264 and DS20 motherboards have an onboard dual-channel Adaptec AIC-7895 SCSI controller, designed in for Windows NT systems, which is disabled because of a bug in the chip. ^{4) 5)}

The console and kernel identify Tsunami family machines by a variation name; a DS20E reports Catamaran: "Booting GENERIC on Tsunami variation Catamaran using machine vector DP264 from SRM". ⁶⁾

The DS20E is a separate design from the DS20, sold as a pedestal or a rackmount system. ⁷⁾

• Up to two 21264 CPUs: 500 MHz 21264 (EV6) with 4 MiB of secondary cache or 667 MHz 21264A (EV67) with 8 MiB ⁸⁾, and later 833 MHz 21264B (EV68) with 8 MiB ^{9) 10)}. Upgrade kits were KN310 for 500 MHz and KN311 for 667 MHz, in per-operating-system variants, of which the -BD suffix is the Linux one. Dual processors must match in speed and cache size ¹¹⁾
• Up to 16 200-pin DIMMs in four banks of four, populated in numerical order with four identical DIMMs per bank, up to 4 GiB ¹²⁾
• Five 64-bit PCI slots and one slot shared between 64-bit PCI and 16-bit ISA; slot 1 takes half-length cards only ¹³⁾
• A combination IDE CD-ROM and floppy drive, one half-height removable media bay, and a disk cage holding either four 1.6-inch hot swap drives on an Ultra2 backplane or six 1-inch drives on an Ultra3 backplane ¹⁴⁾
• Two 375 W power supplies with a bay for a third, sharing a single power cord; the system powers down as soon as fewer than two are running ¹⁵⁾; two serial ports, one parallel port, an Ethernet port, keyboard, mouse, and a USB port that Compaq did not support ¹⁶⁾
• Other onboard devices, as listed in the Linux boot log in the reference guide, are an SMC37c669 Super I/O, two DS21142/3 Tulip Ethernet controllers, and the ATAPI CD-ROM on ide0 ¹⁷⁾
• The DS20E has the same onboard AIC-7895 SCSI controller as the DS20, in PCI slot 6; the SRM console lists it, but Compaq's release notes say that it is not supported on the DS20E (see Conflicting information) ^{18) 19)}

• On the DS20E, the SRM console's os_type variable takes unix or vms, and both start the SRM console at power-up or reset. ²⁰⁾
• The DS20E's remote management console (RMC) can be reached only through COM1. Its default escape sequence is Ctrl+] Ctrl+] rcm (not rmc), which gives the RCM> prompt, and quit returns to the console. ²¹⁾ For the serial console itself, see Using the SRM Console: Serial console.

Current kernels support the DS20 and DS20E, with CONFIG_ALPHA_DP264 or a generic kernel, booted from the SRM console with aboot. Compaq documented Linux alongside Tru64 UNIX and OpenVMS in the DS20E reference guide, which calls for SRM V5.6-3 or later; ²²⁾ the final version is V7.3-1 (see Final versions). See Tsunami systems for notes shared with the other Tsunami machines.

• The DS20E's onboard DS21142/3 Ethernet controllers use the tulip driver. ²³⁾
• Add-in QLogic SCSI cards (qla1280) need firmware from linux-firmware, which installers do not always include. ^{24) 25)}

• Power: a DS20E draws about 500 W at idle. ²⁶⁾ Its power supplies are universal, auto-ranging units for 100 to 240 V. ²⁷⁾
• Weight and noise: a pedestal DS20E weighs 36 kg typically and up to 40 kg. ²⁸⁾ The declared noise level is 46 to 47 dBA at the bystander position with no disk or one, and 51 dBA with six disks. ²⁹⁾
• Missing second CPU: on some early DS20 CPU modules the second CPU could disappear from the configuration after a power cycle; show cpu shows whether both are present. Later module revisions fix the problem. ³⁰⁾
• CPU daughtercards: ES40 CPU daughtercards do not fit a DS20, and not every DS20 CPU module can be paired with every other; see Common problems. ³¹⁾

The following sources conflict with each other or with the account given above. They are listed here for further investigation.

• DS20E onboard Adaptec SCSI
  • AlphaServer DS20E / AlphaStation DS20E Release Notes, p. 3: "The USB and the Adaptec controller are listed in the console show config command display, but they are not supported on the DS20E."
  • "Re: systemd woes continue", Frank Scheiner, debian-alpha, 17 Jul 2019: the DS20E and DS25 "have integrated Adaptec SCSI controllers", which are not affected by the missing QLogic firmware.