>>>Someone asked the question about what good are reading tapes NL. >>>There are valid reasons and these go back to the early years before >>>diskettes, etc, when people wanted to tansfer data. Early, early on >>>the universal mode of transfer was 7-track tape, BCD, Even-parity >>>with no labels. > >> Even parity universal? I'm practically positive that you go back to >> the 7090 and 7094, where odd parity was the norm. > >For NRZI, which was common before phase encoding of 1600BPI, >odd parity is best. I believe, though, that even parity was >all to common for 7 track tape. With even parity, one can't >write the character with all bits zero, as it results in no >magnetic transitions on the tape. A character is recognized >by at least one track having a magnetic transition. > >I don't know specifically which systems allowed/used >even parity seven track, but I do recall that it was used.
There was the fortune or maybe misfortune in the US Government of having IBM lose a court case for 35+ IBM systems in the Dept of Defense back in the late 1960s or early 1970s. A Federal judge ruled it stifled competition and therefore he carved up the award to so many Honeywell, RCA, CDC, SDS, DEC, etc, and a few IBM thrown in for good measure. So I there was a need to send data from one computer to another. 7trk, BCD, Even Parity, and no labels worked the best for me if indeed the other computing center said they could do 7 track tapes. Just simply asking for 9 track might bring some unknown type from a Brand-X system. Even with IBM systems the tape might have a paper label saying it was 9-trk and could not be read. My first shot was to try to 7-trk and most time I got lucky indeed it was. Those were very interesting times. Jim ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
