Some links to one of my favourite Unices (IRIX is probably still my fave in terms of an elegant workstation OS). Nowadays it has to be said the only contenders in the commercial Unix race are Solaris and AIX with various Linux distributions leading the open-source charge.

Personally I've found Tru64 on Alpha hardware to be very very simple to install (for Tru64 v 5.1b its still a single cd install with a footprint less than 400Mb) and configure while being very easy to manage and with outstanding stability. In my time I've had the pleasure of using everything from Alphastation 500's through to quad processor ES45 Alphaservers.

In a high performance environment I have good anecdotal evidence to suggest that the same code running on a dual processor Itanium II machine will run at about 40% the speed of slightly older quad processor Alpha machine. So the Itanium has a lot of potential but the Alpha can still hold its own.

The Alpha hardware is also built to a very high spec and very very solid (I guess its easy to see the DEC influence in the steel chassis) compared to the 'cheap' feel of modern x86 based server cases.

Wikipedia has some excellent (and brief) articles on:

The history of Tru64/Ultrix/OSF/1.

The history of the Dec Alpha processor.

The evolution of OpenVMS.

Excellent Tru64/Alpha resource - Tru64.org.