The DEC 4000 AXP was part of the first generation of Alpha CPU based systems. Positioned as a departmental server, it was larger than the DEC 3000 AXP workgroup server, but smaller than the DEC 7000 AXP enterprise server. Originally, there were two models, 610 and 620, with 1 or 2 160MHz CPUs. Later, models 710 and 720 were added, with 190 MHz CPUs. All three of my DEC 4000s seem to have started life as a model 610 (according to the stickers on the back), but a second CPU was added to each of them later, turning them into model 620s. I changed one of them back to a model 610, by removing a (broken) CPU module.
CPU, memory, I/O and power supplies are all situated at the back of the machine, leaving room in front of the machine for storage. There are 4 disk drawers, each of which can hold up to 4 disks. The disk controllers these connect to can be set to either SCSI or DSSI mode.