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Iván Izaguirre
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DOS turns the drive off at the end of each access. At the start of the next it reads the data latch eight times, comparing each read with one 14 cycles later, to tell whether the disk still turns; if it does not seem to, it waits for the motor to come up to speed, close to a second. With the Disk II card and a DSK, PO or NIB diskette that wait was paid on every access, and a DOS 3.3 boot took 36 million cycles where the real machine takes five. Two things made the disk look still: - The motor stopped as soon as the drive was turned off. The 556 timer of the controller keeps it turning for about a second, as the sequencer card already does, and the writable diskette does not move while stopped. - The diskette gives a nibble on every read, and the 48 0xff sync nibbles of the gap after a sector, where an access ends, read the same sixteen times in a row. The latch of a turning disk is never the same nibble twice: it holds the next one being shifted in, with bit 7 clear. Every other read now gives that, which programs reading nibbles skip. DOS 3.3 reaches its banner in 5.4 million cycles, and the System Master loads Integer BASIC in 4.7 million where it took 59 million, as with the WOZ image on the sequencer card. Tests pin the boot time and check that a diskette INIT formats starts the machine.