Abstract: A disk array system comprises a host computer, a plurality of parallel I/O interface disk drives on backplane, for example, ATA or SCSI disk drives, and a disk array controller. The disk array controller includes a local PCI bus and serial I/O interface controllers for coupling the parallel I/O disk drives to the host computer. The disk array controller is operatively configured to control the parallel I/O interface disk drives by the serial I/O interface controllers. The serial I/O interface controllers act as bus masters with respect to the local PCI bus, and access the parallel I/O disk drives through the local PCI bus read/write cycle operation. By way of controlling the parallel I/O interface disk drives through serial I/O interface controllers, the limitation on the effective transmission length inherently in the parallel I/O interface cable is loosened and the disk array controller is capable of controlling more disk drives.