The AlphaPC 164UX is an ATX form factor motherboard based on the EV56 (21164A) microprocessor and the 21174 core logic chip. It was designed by DeskStation Technology under the code name "Ruffian", which is also the name of its Linux platform. It can only boot Linux through MILO, and no current kernel has been reported to boot on it; see Linux.

• Alpha 21164A CPU at 466, 533, or 600 MHz, the same CPUs as the AlphaPC 164LX; the clock is selected by jumpers ¹⁾
• 2 or 4 MiB onboard L3 backup cache (synchronous SSRAM)
• 21174 core logic chip
• 6x 168-pin DIMMs (three banks), supports 32 MiB to 1.5 GiB of unbuffered ECC SDRAM. The manual's specifications give 3 GiB, but its configuration table ends at 1.5 GiB with 256 MiB DIMMs, ²⁾ and 1.5 GiB is the largest configuration reported in use. ^{3) 4)}
• 1x 33 MHz 64-bit PCI slot
• 5x 33 MHz 32-bit PCI slots
• 1x ISA slot
• DEC 21052 PCI-to-PCI bridge
• Intel 82371SB PCI-to-ISA bridge and EIDE
• DEC 21143 10/100 Mbit Ethernet
• Symbios 53C875 Ultra Wide SCSI controller
• SMC FDC37C666 Super I/O controller (floppy, 2x serial, parallel)
• PS/2 keyboard and mouse
• 1 MiB flash ROM
• DeskStation ARCSBIOS firmware (for Windows NT)
• ATX board, 30.48 cm x 24.38 cm (12.0 in x 9.6 in), with mounting holes to the ATX 2.01 specification; the board exceeds the ATX height limits at the CPU and at the SCSI connectors ⁵⁾

All configuration jumpers are on block J28: ⁶⁾

Options 6, 10, and 12 are reserved and left out. ⁷⁾

The AlphaPC 164BX is the same board as the 164UX, except that it lacks the Ethernet and Ultra Wide SCSI controllers and has only a 2 MiB L3 cache.

The only firmware for the board is DeskStation's ARCSBIOS, which is distinct from both ARC and AlphaBIOS. No SRM console or AlphaBIOS was ever released for it, so operating systems and installers that require SRM cannot be used. ^{8) 9)}

• ARCSBIOS updates are flashable, and the last versions (a few Y2K updates) were distributed by API, which never had the ARCSBIOS sources. ^{10) 11)}
• The alphalinux/firmware repository keeps ARCSBIOS images 1.3.061 (UXbios_1.3.061.tgz) and 1.3.062 (UXbios_1.3.062.zip, files dated November 1998), together with the user and technical reference manuals. ¹²⁾
• If the primary image cannot be loaded, the Safe ARCSBIOS starts automatically, signaled by one long and two short beeps; it can also be selected with J28 option 11. It is used to reflash the firmware. ¹³⁾
• There is no flash management utility for loading MILO into the flash ROM. ¹⁴⁾

Current kernels include support for the board (CONFIG_ALPHA_RUFFIAN, or a generic kernel), ¹⁵⁾ but it can only boot Linux through MILO, and Linux 2.6.22.19 is the last kernel reported to boot on it; 2.6.23 was the first that did not. ¹⁶⁾ The cause is the PT_NOTE program header that Linux 2.6.23 added to the kernel image, which MILO mistook for a loadable segment. A MILO fix was committed in May 2026, but has not yet been tested on a 164UX. ¹⁷⁾ See MILO: Booting Linux.

The onboard devices are supported by these drivers:

• IDE (Intel 82371SB, PIIX3): ata_piix ^{18) 19)}
• Ethernet (DEC 21143, 164UX only): tulip ²⁰⁾
• SCSI (Symbios 53C875, 164UX only): sym53c8xx ²¹⁾

ARCSBIOS starts MILO through a DeskStation-specific loader, ldmilo.exe; the linload.exe used on AlphaBIOS systems does not work, because ARCSBIOS has its own console application interface. The version of ldmilo.exe later rebuilt by DEC works much like linload.exe, except that the MILO image must be named milo. ²²⁾

• ldmilo.exe, MILO, and the PALcode go on a small FAT partition, and an ARCSBIOS boot entry points OsLoader at ldmilo.exe and passes MILO commands in OsLoadOptions. ²³⁾
• The board cannot boot from CD-ROM, only from floppy or a FAT partition on a hard disk. ²⁴⁾ Current distribution installers, which boot from SRM, cannot be used.

• Onboard Ethernet: the 21143 often fails to auto-negotiate, particularly at 100 Mbit. ^{25) 26)} Forcing the media type (for example options tulip options=14 for MII 100baseTx full duplex) may help. ²⁷⁾
• Memory: boards with four DIMMs are sensitive to the choice of modules, because the 21174 does not drive the memory lines to the JEDEC standard; the AlphaPC 164LX, which uses the same chipset, is affected in the same way. ²⁸⁾ Hard Data shipped UX systems with up to 1.5 GiB using selected modules. ²⁹⁾
• PCI slots: the onboard SCSI controller is behind the 21052 PCI-to-PCI bridge. ³⁰⁾ A VGA card used as the console must be in the single 64-bit slot, in front of the bridge. ³¹⁾
• Real-time clock: the RTC chip is soldered to the board. A 164UX that powered on but did not work was repaired in 2026 by replacing the RTC chip, after the old one was removed and a socket fitted. ³²⁾

DeskStation Technology designed the board and its firmware, and sold it as the Ruffian RPX164-2. DeskStation ported Linux to it in 1997, while prototypes were already running Windows NT at 633 MHz. ^{33) 34)}

Around late 1997, the rights to the design and to the ARCSBIOS firmware were bought by Samsung, which set up its Alpha subsidiary Alpha Processor, Inc. (API) in 1998, and the board was renamed AlphaPC 164UX/BX. ^{35) 36) 37) 38)} Samsung boards are labeled UX2 and UX4 after their L3 cache size. The cache chips are soldered to the board, so a 2 MiB board cannot be upgraded to 4 MiB. ³⁹⁾

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

• Maximum memory
  • AlphaPC 164UX/BX Motherboard Windows NT User's Manual: "Main memory 32MB to 3GB memory array"
  • "Ruffian maximum memory and debian", unai, debian-alpha, 12 Nov 2002: "the user's manual tell one place up to 3GB, but in other place up to 1,5GB"
  • "Re: hardware ramblings Re: Request For Comment: ", Maurice Hilarius, axp-list, 11 Apr 2001: "the UX version with 1.5GB capacity."