The rx4640 is a zx1 based 4U server from HP.
It can have up to 4 Madison processors.
It supports either 16 or 32 DIMM slots which must be loaded in quads. Supported DIMM sizes are 256MB to 2GB.
It has 8 PCI-X slots. Slots 1 and 2 are used for core IO (SCSI and Ethernet). Slots 3-8 are hotplug capable. Slots 7 and 8 have 1GB/s bandwidth each. Slots 1 and 2, 3 and 4, and 5 and 6 are paired, sharing 500MB/s bandwidth between each pair of slots.
On the motherboard, there are EHCI USB ports, an IDE DVD-ROM drive and Diva serial ports / network console. It has two internal SCSI drive bays which support Ultra320.