Browse Prior Art Database

Method to Dynamically Adjust for Tape Speed Variations

IP.com Disclosure Number: IPCOM000050258D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Milling, PE: AUTHOR

Abstract

Described herein is a method to dynamically adjust for tape speed variations by updating data bit decision rules based on the most recent data bits read. This method decreases the probability of making an error when deciding whether a data bit read from a cassette tape is a "0" or a "1" by dynamically adjusting the decision rule based on the duration of previously decoded data bits.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 1

Method to Dynamically Adjust for Tape Speed Variations

Described herein is a method to dynamically adjust for tape speed variations by updating data bit decision rules based on the most recent data bits read. This method decreases the probability of making an error when deciding whether a data bit read from a cassette tape is a "0" or a "1" by dynamically adjusting the decision rule based on the duration of previously decoded data bits.

As background, it is assumed that each data bit is stored on a cassette tape as a square wave; for instance, a "0" bit is assumed to be stored on the tape as a 500-microsecond period square wave (Nominal "0" Size equals 500 microseconds), and a "1" bit is stored on the tape as a 832-microsecond period square wave (Nominal "1" Size equals 832 microseconds). The period of each square wave read from the tape is determined and used to decide whether the data bit is a "1" or a "0".

A static decision rule would be to decide that a data bit is a "1" bit if its measured period is greater than the mid-point between the Nominal "1". Size and the Nominal "0" Size values. This value can be computed by adding the Nominal "1" Size to the Nominal "0" Size and dividing by 2. Thus if the detected period is less than 666 microseconds, it is assumed to be a "0" bit, and if it is greater than 666 microseconds, it is assumed to be a "1" bit.

The static decision rule can lead to errors if the tape varies its speed during the read mode by a significant smount. It is preferable to utilize a dynamic decision rule whereby the real time basis is adjusted for the Expect...