Abstract: A system and method are disclosed for providing computers, particularly the Unisys A series computers, with the capability to function with disk drives of more than one sector format, especially if a predetermined sector format is inefficient and/or cost prohibitive. Interfacing is provided for processing I/O requests between a predetermined logical sector format (e.g., 180 byte sectors) and a variable physical sector format (e.g., 512 or 720 byte sectors). Read operations compare read request addresses to physical sector boundaries and discard unwanted data. Write operations, using at least one sector buffer, perform a read/modify/write cycle, such that the necessary physical sector data not associated with the write request is read into the sector buffer, modified and written back to the disk along with the write data inserted at the appropriate location. This system and method can effectively increase the usable capacity of selected disk drives by 15-20%.

Abstract: A non-return-to-zero synchronizer is described which creates an output pulse signal that is synchronized to a system clock signal, from an asynchronous input strobe signal which can occur at any point in a given system clock cycle. The first circuit element within the synchronizer captures the input strobe and toggles the state of its data output terminal in response to successive pulses of the asynchronous input strobe signal. The remaining portion of the synchronizer responds to each change in the state of the first circuit element and to produce an output pulse having a duration of one clock cycle. An alternative embodiment is described which utilizes a sequential logic circuit to generate the desired output pulse. Because the synchronizer uses a state change to indicate the occurrence of a strobe, the problem of resetting the initial circuit element to a particular logic level is eliminated.