The AlphaPC 164 is an ATX form factor motherboard produced by Digital Semiconductor. It is a member of the EB164 family (along with the EB164, AlphaPC 164LX, and AlphaPC 164SX), and was the first Digital Semiconductor board to use the 21164A (EV56) CPU. ^{1) 2)} Before release it was sometimes called the "EB164+". ³⁾

• 366, 400, 433, 466, or 500 MHz 21164A (EV56) CPU ⁴⁾; the original 21164 (EV5) is not used ^{5) 6)}
• 21172 core logic chipset (CIA-2)
• One bank of 4 or 8 36-bit 70 ns SIMMs, supports 16 MiB to 512 MiB of DRAM (128-bit or 256-bit data bus)
• 1 MiB synchronous SRAM L3 cache
• 4x 33 MHz PCI slots (2x 64-bit, 2x 32-bit)
• 2x ISA slots
• Intel 82378ZB PCI-to-ISA bridge
• CMD PCI0646 IDE on PCI
• SMC FDC37C935 Super I/O controller (floppy, 2x UARTs, parallel port, keyboard and mouse, time-of-year clock)
• 1 MiB flash ROM
• Windows NT ARC firmware or SRM console (see Firmware)
• ATX form factor power supply with a high-current 3.3V rail (see Power Supply)
• 12.0 in x 9.6 in (30.48 cm x 24.38 cm)

The board is configured with jumper blocks J1, J30, and J31. ⁷⁾

• The CPU speed is set by the clock oscillator (crystal) together with the speed-select jumpers described in the Technical Reference Manual. Changing speed requires a crystal of the matching frequency, e.g. 50.0 MHz for 500 MHz. ⁸⁾
• The CPU supports the EV56 byte/word extension (BWX), so code compiled with -mcpu=ev56 runs on the board. ⁹⁾ The 21172 core logic cannot make byte and word accesses to I/O space, so the kernel uses sparse I/O addressing on this board.
• The CPU fan has a rotation sense connection, and the board will not run without a working fan. ¹⁰⁾

• SIMMs are installed 4 at a time: 4 SIMMs give a 128-bit memory bus and 8 SIMMs give a 256-bit memory bus. All installed SIMMs must be the same size, so the maximum of 512 MiB requires 8x 64 MiB SIMMs. ¹¹⁾
• Standard page mode DRAM SIMMs are required; EDO SIMMs offer no benefit and may not work. ¹²⁾
• 1 GiB configurations, beyond the documented maximum, have been reported to work only with modules from one vendor. ¹³⁾

• The board does not drive the ATX PS_ON signal, so a standard ATX power supply will not turn on unless PS_ON (pin 14) is connected to ground, e.g. with a latching switch. ^{14) 15)} Some boards have a factory rework wire tying PS_ON to ground, so they power on whenever the supply has AC power (see pc164-engineering-fix.jpg in the gallery).
• A 500 MHz 21164A draws about 11.5 A from the 3.3V rail, and the board itself about 5 A more, which exceeds the 3.3V capacity of many ordinary ATX power supplies. ¹⁶⁾
• The time-of-year clock battery is a replaceable CR2032 coin cell at B1. ¹⁷⁾ A depleted battery causes a variety of firmware problems. ¹⁸⁾

• Boards were sold with either the ARC console (for Windows NT and Linux) or the SRM console (licensed for Digital UNIX). ¹⁹⁾
• Only one console fits in the flash ROM at a time. With SRM in flash, the ARC firmware can be loaded from a FAT floppy using the arc command. ²⁰⁾
• Firmware is updated with fwupdate.exe from a floppy. If the update fails from the console, the fail-safe loader can be used with the firmware image and update utility on a DOS floppy. ^{21) 22)}
• AlphaPC 164 firmware development stopped before that of the 164LX and 164SX. ²³⁾ The last SRM release is V5.6. ^{24) 25)} The SMMTABLE.TXT file on the V7.3 firmware CD lists SRM 5.5 as the last version for the board but names no update file for it (the entry is [ARCHIVE]NOFILE.EXE). ²⁶⁾
• The SRM console only probes the primary IDE channel, so devices on the secondary channel cannot be booted from SRM (Linux can use them). ²⁷⁾
• SRM cannot boot from Adaptec 2940UW or 39160, Symbios 53C895, or Mylex DAC1164P controllers. The KZPCM (IntraServer 4280UE-4, with two NCR 53C875 channels) works for both disk and network booting. ²⁸⁾ Network booting from SRM works with Digital Ethernet cards such as the DE435, DE450, and DE500. ²⁹⁾
• With SRM V5.5-1, the Matrox Millennium, ELSA Gloria Synergy (Permedia 2), 3Dlabs Oxygen VX1 (Permedia 3), Diamond Stealth III S540 (Savage4), and TGA/TGA2 cards work as console devices, but the 3dfx Banshee does not. ³⁰⁾ ATI Radeon (R100, RV100, RV200) cards do not work with SRM, but do work with ARC and MILO. ³¹⁾

Current kernels support the AlphaPC 164 with CONFIG_ALPHA_PC164 or a generic kernel; it boots from SRM with aboot. ³²⁾ Linux treats the board as the PC164 variation of the EB164 family. ³³⁾ The onboard CMD646 IDE controller uses the pata_cmd64x driver. ³⁴⁾

The SMC FDC37C935 Super I/O controller's devices use the standard PC drivers:

• Serial ports: 8250, at the standard PC addresses listed in the Alpha serial port table. ³⁵⁾
• Parallel port: parport_pc; floppy: floppy; keyboard and mouse: i8042. ^{36) 37) 38)}
• Clock: the Alpha platform code reads the time-of-year clock itself rather than using rtc-cmos. ³⁹⁾

• Interrupt masking: the interrupt masking hardware is broken, so Linux relies on a software workaround, CONFIG_ALPHA_BROKEN_IRQ_MASK, which PC164 and generic kernels enable automatically. ⁴⁰⁾ Without it the system hangs under heavy network or disk load. ⁴¹⁾ SRM reports the board as the EB164 variation rather than PC164. ⁴²⁾

• The Aspen "Durango" is Aspen's name for the AlphaPC 164. ⁴³⁾
• Vobis, a German computer retailer, sold systems based on the AlphaPC 164. ⁴⁴⁾

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

• Maximum memory
  • AlphaPC 164 Motherboard Product Brief: "16MB-to-512MB memory array"
  • "Re: 1 GB RAM in PC164", Wolfgang Dreyer, axp-list, 13 Jun 1997: "Yes but as far as i know only one vendor of memory modules worldwide works."
• CPU speeds
  • AlphaPC 164 Motherboard Product Brief: "366, 400, 433, 466, and 500 MHz"
  • "Re: Kernel 2.4.17", Jay Estabrook, axp-list, 8 Jan 2002: "PC164 EV56 (433-500) CIA-2 AlphaPC164"