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Browse Prior Art Database

Floppy Disk Rotational Position Prediction

IP.com Disclosure Number: IPCOM000053023D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Evangelisti, CJ: AUTHOR [+2]

Abstract

A method is described for predicting the rotational position of a floppy disk device. Significant performance advantages are possible if a program can predict the current rotational position of the read/write head on a disk I/O device.

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Floppy Disk Rotational Position Prediction

A method is described for predicting the rotational position of a floppy disk device. Significant performance advantages are possible if a program can predict the current rotational position of the read/write head on a disk I/O device.

Augmentation to the type of controller normally used with floppy disk devices is shown in the figure and consists of a program-accessible clock 1, a rotational synchronization procedure 2 and a rotational prediction procedure 3. These elements could be embodied within a microprocessor replacement for existing controllers or as an add-on to existing controllers for a floppy disk file 5.

The program-accessible clock, a common feature of a microprocessor, must have sufficient resolution to match the speed of the drive (normally 32 microseconds per byte). This could be the same 1 MHz clock required by the controller itself. The clock is used by the sync routine 2 to compute a reference time 4 and by the predict routine 3 to predict the disk head position shown at 6.

The purpose of the sync routine 2 is to compute the reference time 4. This is the time when the read/write head was last positioned at some standard reference point (e.g., track index point, or beginning of sector 1). This is done by first initiating a read of some known position on the current track (e.g., the next sector identification field). On completion of the read operation, the clock is read. Thus, we know the position of the read/write head at some known time. From this we compute the reference time 4. For example, for an IBM 3740 disk the following formula gives the number of microseconds...