The Alpha Development Unit (ADU) was a prototype Alpha system on which Digital did its operating system work before any Alpha system shipped; it was never sold. ¹⁾

The ADU consisted of: ²⁾

• A washing-machine-sized box holding the Alpha prototype hardware
• A DECstation 5000 on top, acting as host, I/O processor, and front end
• The two communicated over TURBOchannel, with the ADU appearing to the DECstation much like a TURBOchannel option

ULTRIX ran on the ADUs first, then OSF/1, whose development continued on them until the first DEC 3000 Model 500 (Flamingo) systems arrived. Support for the ADU was dropped before the first release of DEC OSF/1 for Alpha, although some engineers inside Digital kept theirs running through the first two releases. ³⁾

ULTRIX on Alpha was an advanced development effort only. It ran on the ADU, was never carried to the production machines, and was never a product. ⁴⁾ OpenVMS first booted on Manniquin, an EVAX emulator running on a VAX, before it ran on the ADU. ⁵⁾