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Method Of Assigning Separate Physical End Of Tape (PEOT) Points On A Tape Device For Read Forward And Write Commands

IP.com Disclosure Number: IPCOM000052084D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Kirkpatrick, CR: AUTHOR [+3]

Abstract

The position of the tape on a tape drive is known to the microcode by counting tachometer (T2) pulses from a 500-line tachometer on the file reel, between each tachometer (T1) pulse from a single line tachometer on the machine reel. This count represents a radius on the file reel, since the tape on the file reel is manufactured to a radius tolerance.

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Method Of Assigning Separate Physical End Of Tape (PEOT) Points On A Tape Device For Read Forward And Write Commands

The position of the tape on a tape drive is known to the microcode by counting tachometer (T2) pulses from a 500-line tachometer on the file reel, between each tachometer (T1) pulse from a single line tachometer on the machine reel. This count represents a radius on the file reel, since the tape on the file reel is manufactured to a radius tolerance.

BOT (beginning of tape) and EOT (end of tape) therefore can be represented by a certain count' Another count, PEOT (physical end of tape is used to prevent pulling the tape off the file reel.

Two values (counts) are used for PEOT. The lowest count (farthest in from actual tape end) represents the radius for PEOT when in a Write Mode. Another higher count (nearer to actual tape end) represents the radius for PEOT when in a Read Mode. In either case, when PEOT is reached, the tape stops and the tape drive will not accept any forward commands.

This Write-Short Read-Long condition ensures that all data written on a tape can be read by any tape drive, and yet prevents tape from being pulled off the file reel. All functions are microprocessor-controlled. The flow chart for the control is illustrated in the figure.

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