This paper describes the electrical architecture and design of the IBM eServere BladeCentert processor blades, expansion blades, and input/output (I/O) expansion adapters and units. The processor blades are independent, general-purpose servers containing processors, chipsets, main memory, hard drives, network interface controllers, power input control circuitry, and local systems management. The blade architecture is robust and flexible enough to enable the design of general-purpose Intelprocessor-based two-way and four-way blades, IBM POWEReprocessor-based blades, blades based on AMD Opterone processors, and common expansion blades. In addition, the processor blades, expansion adapters, and units use a serializeddeserialized (SerDes) interface for the internal I/O fabrics, thus giving blades the flexibility to support virtually any I/O protocol that supports SerDes. Support for I/O fabrics beyond the base Gigabit Ethernet is accomplished via optional I/O expansion adapters for Fibre Channel, Myricom Myrinet t, InfiniBand t, or additional Gigabit Ethernet. Additional storage or peripheral component interface capability can be added to the processor blades via expansion blades.