On 6/5/19 10:27 AM, John Labovitz via cctalk wrote:
Character-based I/O on mainframes and even minicomputers was fairly rare
at that point. On some systems it was impossible; on others it was very
CPU-intensive. I remember trying to do character I/O on a Tandem NonStop;
it wasn’t easy, or effective. Having a dedicated microcomputer solved
a lot of problems.
Ah. Now the need for another computer makes sense.
My dad actually built a successful company in the 1980s to do just that:
he build front-end controllers, which were essentially large number
of serial ports connected to a rack of Z80 boards, which would then
be connected to a mini (a Tandem) or mainframe via some bulk-oriented
format. For example, I wrote code for him that let a typical terminal (eg,
Wyse, VT-100) emulate a Univac block-style terminal. All the input, screen
management, etc. was done on the Z80 machines, then shipped over in a
multiplex fashion first to the Tandem and then to a Univac as block forms.
ACK
You’re getting warmer. ;-)
Modems started out as straight modulators-demodulators, connecting two
remote devices (computers, terminals, printers) over a point-to-point
leased line specially installed from the local telephone company —
basically like a T1 line would be installed today. The POTS line was
hard-wired (via screw-down terminals) on one side of the modem and the
digital data connector (eg, DB-25) on the other. Usually the connections
were always on; I suppose the billing was probably by data usage, or
even fixed price, instead of by time.
ACK
We used some 56 kbps (bit robbed) lines for terminal multiplexers at my
job around 2000. They were always on and (I think) just billed at a
monthly rate for the line.
Maybe someone created that monstrosity (;-), but the typical usage was
that you used an acoustic coupler modem that had cups where a typical
handset would fit. The modem itself only had a data connection to the
terminal (or printer or card reader/punch). Next to the modem was a
regular telephone — you dialed the number on the phone, and once
you heard the carrier squeal, you’d quickly set the handset into the
coupler. Usually you’d see a spurt of random characters on the screen
which was the modem getting confused by the carrier being gradually synced
up. To hang up, you’d simply pull the handset out of the coupler and
hang it up as normal.
ACK
I do recall a little handheld device with a touchtone keyboard that you
could fit over the microphone of a normal handset. It wasn’t automated,
but at least you didn’t have to use the rotary dial. (This presumed,
of course, that the telco switch was DTMF-compatible.)
I remember things like that.
I also remember a pager for kids that didn't even have a display. It
simply dialed the number by playing the DTMF tones into a mouth piece.
--
Grant. . . .
unix || die
