This must have been quite a machine when it was new in 2000. The single Pentium III 866 it came with has been upgraded to dual 1GHz Pentium III CPUs (with 133MHz FSB)), RDRAM memory upgraded from 256MB to the full 2GB), and has a 10,000 RPM Ultra 160 SCSI 36GB hard drive (upgraded from a 9GB unit). The graphics card is a Matrox G400 32MB card, a slight upgrade on the original dual head Matrox G400 16MB AGP card.
I was unable to find CPUs with the correct heatsinks, or the heatsinks on their own, for a sane price. Almost noone has them, one company in the States offered me some for a "special" price of $230 each, and there are some on ebay for an even higher price. I ended up buying kits for the Proliant DL380 G1 rackmount servers and modifying the heatsinks to fit the PC, with 3 CPUs (one as a spare) and 3 voltage regulators (part of the bundle), and transatlantic shipping, costing less than the unit price of a single CPU with the correct heatsink. Details of the modifications to the heatsinks can be found here.
Update January 2026: on powering it up I was greeted with a blank screen and one long beep followed by three short beeps. After trying the obvious by reseating the memory modules and processors with no improvment, I consulted the service guide which informs that this beep code means "System ROM is bad; System is running in Failsafe boot block mode", and that the recommended action is "Reflash the ROM using a ROMPaq diskette." In failsafe mode it is possible to reflash the BIOS according to the given procedure, so I prepared a floppy with the correct SoftPaq using the Contura 420C. On booting the AP550 with the floppy inserted, I was greeted with the normal display and no error messages! My assumption is that a part of the BIOS flash is probably slightly corrupted with a bit in an indeterminate state such that it could be read as a 0 or a 1, so therefore judged that it's best to just reflash the BIOS anyway to ensure that the firmware is properly stored. Having done this, I've still had a few odd errors suggestive of potential memory problems, but both Compaq Diagnostics and Memtest86+ haven't been able to identify any fault so far. Fault and resolution therefore TBD. Rather upsetting as this is such a nice machine.
Inside the workstation before the upgrades.
Just look at the heatsink on that Slot 1 Pentium 3. This is the original CPU and heatsink.
And now with more CPUs and RAM :-D
A close up with the new CPUs and the additional VRM needed for the second CPU. Part 329267-001 is the original option part, but I couldn't get one. Part 327563-001 didn't work, but 155681-001 works fine.
Showing both CPUs working
