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Dicell Gray Coding of Disk File Track Addresses

IP.com Disclosure Number: IPCOM000049797D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Pennington, DH: AUTHOR

Abstract

Disk file servo systems using sectored position information typically must derive track-crossing information indirectly during the seek mode. This usually involves building a hardware model of the system to simulate track crossings. Track-crossing information is vital during the seek, in that it provides an accurate means for calculating the distance yet to be traveled.

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Dicell Gray Coding of Disk File Track Addresses

Disk file servo systems using sectored position information typically must derive track-crossing information indirectly during the seek mode. This usually involves building a hardware model of the system to simulate track crossings. Track-crossing information is vital during the seek, in that it provides an accurate means for calculating the distance yet to be traveled.

An alternate method for calculating the distance to travel is to read the track address at sector time and subtract it from the desired track address. This is an accurate and direct means of deriving distance to go without the need for a hardware model of the system.

In order to read the track addresses during the seek mode, the addresses must be readable whether or not the head is centered over a track. If addresses are to be read while the head is off the track, it is critical that the address on the adjacent track not interfere with the read process. Instead, the adjacent address should support the read process except for resolving the least significant bit, which describes specifically which of the two tracks the head is over. This is achieved by Gray Coding the addresses so that only the least significant bit differs between addresses. In addition to Gray Coding, the address bits must further be encoded so that adjacent bits don't magnetically cancel out each other.

A working means of Gray Coding the track addresses is as follows. Fig. 1 illustr...