Drive Selector

This circuit makes it possible to use double-sided disk drives with a computer that supports only single-sided units. Many of the older generation of com- puters were designed to oper- ate in conjunction with Shugart- compatible, single-sided disk drives. These have rapidly been superseded, however, by the more economical double- sided drive, which has a greater storage capacity. The Shugart standard supports the use of four disk drives, which are selected with drive select lines DSO-DS3. Two further lines, HS0 and HSI , con- trol the head selection on each of these drives. When this cir- cuit is installed between the computer"s disk controller out- put and two double-sided drives, the disk operating system (DOS) can recognize four logical drives. When the computer selects drive A or B, the situation is similar to before the conversion. Selection of drive C or D, however, causes the second head in the relevant drive A or B to be activated. In this way, the total storage capacity o...