Modular unitary disk file subsystem having increased data storage

Abstract

Higher data storage capacity is realized in a self contained fixed rotating disk expansion board subsystem preferably for a single electronics circuit board accessory slot of a host computer. This greater capacity, e.g. 42 megabytes of formatted storage on two 95 millimeter disks, is achieved by use of a plural zone arrangement wherein each zone contains data tracks in which user blocks are recorded and read out at a data rate unique for the zone. An improved phase locked loop within the data separator uses a separate voltage controlled oscillator for each zone and a commmon charge pump for generating control voltages applied to change the resonant frequency of all of the oscillators, An oscillator disable circuit disables every voltage controlled oscillator other than the selected oscillator, so that it is the only oscillator whose frequency is actually varied by the charge pump during readback/data separation and decode operations. A dual latch circuit extends the margin of a data window in the data separator to ensure that legitimate data bits read back from the data surface are latched for separation. A single microprocessor supervises operations of the subsystem and calculates physical sector location within each zone from logical sector location data supplied by the host computer.