Patent ID: 8200870

Claim:
A switch coupled between a plurality of host units and a device for communicating therebetween and comprising: a) a first serial advanced technology attachment (SATA) port coupled to a first host unit and including a first host task file, said first port for accessing the device by the first host unit, the first host task file responsive to commands sent by the first host unit; b) a second SATA port coupled to a second host unit and including a second host task file, said second port for accessing the device by the second host unit, the second host task file responsive to commands sent by the second host unit; c) a third parallel ATA (PATA) port including a device task file, coupled to a device, for accessing the device by the first or second host units, the device supporting queuing of commands sent by the first and second host units and generating an original queue depth value indicative of the number of commands that the device can queue from either of the first or second host units; and d) an arbitration and control circuit, coupled to said first host task file, said second host task file and said device task file for selecting one of the first host or second host units to concurrently access the device, through the switch, by accepting commands, from either of the first or second host units, at any given time, including when the device is not in an idle state, the arbitration and control circuit being responsive to the original queue depth value and altering the original queue depth value to be an altered original queue depth value so that when the original queue value is odd, the altered original queue depth value is one half of the original queue depth value after subtracting one so that each of the first and second host units is assigned less than the number of commands indicated by the original queue depth value but that a total number of commands queued by the first and second host units remains the same as the original queue depth value thereby misrepresenting the original queue depth value to the first and second host units to be less than the original queue depth value thereby preventing commands sent by the first and second host units from being lost by an overrun of the original queue depth value by either of the first or second host units.