[OT] More tape drive stories
Jerry Feldman
gaf at blu.org
Mon Sep 18 09:52:00 EDT 2006
On Monday 18 September 2006 8:55 am, Jon maddog Hall wrote:
> My favorite tape, for many reasons, was the Link Tape, often called "DEC
> TAPE".
The DEC Tapes were great. As you mentioned, the tracks were duplicated where
on a standard 9-track tape there was a parity bit (hence 9-tracks, 8 bits
of data, 1 parity). Another thing about DEC Tapes is that they were
effectively random access. The home position was in the center with an
equal amount of tape on the left and right reels.
WRP Punched Paper tape - remember that well from both graduate school and
Burger King. The Burger King POS in the early 1970s was a PDP8-M with no
front panel, an integrated modem, and up to 4 registers (each register was
shared by 2 clerks).
For the modem, we placed the bits(10 - 8 data + start + stop) in the
accumulator, and shifted the bit to be sent into the link, looped for the
number of MS equivalent to 1200bps, and sent the next one. The printer was
a drum printer where we formatted the accumulator for bits to strike the
hammers. The system had a power fail board, and non-volatile core memory
(4K 12-bit words except in Connecticut where we needed 8K). We would upload
program changes after we completed the data transfer. If the system needed
to be reloaded manually, a service guy had to be dispatched. He had to
remove the front panel, insert the paper tape board, and reload the program
from the paper tape reader in his kit. I believe that the ROM on the system
included the RIM loader (this was a short but inefficient paper tape reader
used to boot the real paper tape reader - Most of us PDP8 people used to
have to key this in by hand). BK used this in its stores until a
commercial microprocessor system was available at 25% of the price in about
1976 time frame. With 4K we could do the normal POS, save hourly sales,
inventory, and a few other things. We even added timecard data (by adding
another 8K - this never made it to production).
--
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix user group
http://www.blu.org PGP key id:C5061EA9
PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9
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