The iSBC 21SG board design is based on the Intel 8089 8/16-Bit HMOS I/O Processor which features direct-memory-access (DMA) transfers, multiple-sector transfers, transparent error detection and correction (with automatic recovery and retry) and data management. The board operates in a multiprocessor environment and is fully compatible with all Intel 8- and 16-bit computers. The number of tracks per surface is software selectable for each drive unit. Seek operations on more than one drive can be overlapped with read/write operations on other drives.

The iSBC 21SG board is fully compatible with Intel 8~86 16-Bit HMOS Microprocessor 2~-bit addressing. and can be used in Intel MULTIBUS 24-bit address systems. The board includes two Intel iSBX bus connectors. J3 and J4. that allow other storage devices such as flexible-diskette drives or magnetic cartridge-tape drives to be operated with MULTIBUS interface compatible systems. For example: the Intel iSBX 218A Flexible Diskette Controller Board attaches to iSBX bus connector J4 allowing the iSBC 21SG board to control as many as four flexible-diskette drives.

As another example the Intel iSBX 217B/C Magnetic Cartridge Tape Interface Board attaches to iSBX bus connector J3. allowing the iSBC 21SG board to control as many as four tape drives.

The iSBC 21SG board is a single, multi-layer printed-circuit board assembly. It may be installed in any Intel backplane or custom-designed configuration that is physically and electrically compatible with the Intel MULTIBUS interface.
The host central processing unit (CPU) communicates with the iSBC 21SG board via four blocks of information in host memory. Once the iSBC 21SG board is initialized. a CPU I/O write to the board wake-up address initiates activities. The board accesses the four blocks in the host memory to determine the specific operation being performed, fetches the required parameters. and completes the specified operation without CPU intervention.