Four clusters of 16 CPU's each are each associated with a solid state memory and a main memory. Each CPU is uniquely associated with a channel arbitrator which interconnects the associated CPU to serial ports. Each channel arbitrator is associated with a set of 16 serial channels. Each serial channel is in turn interconnected to a channel adapter which includes software and firmware adapted for interacting with a specific peripheral device. Each channel adapter also has software and firmware which is device-independent for data transfer with the channel arbitrator. The channel arbitrator includes a memory port for accessing main memory through the CPU, a port for accepting service requests and providing interrupts to the CPU's, direct memory access control logic, arbitration control logic, serial ports associated with the channel adapters, and a parallel port is associated with solid state memory. Direct memory access requests are queued at the channel while higher-priority serial transfer requests are serviced. Direct memory access is provide in 64-word blocks designated by perimeter packets indicating a number of blocks, starting address in main memory, starting address in solid state memory, and an indication of the direction of transfer.