Modems and external dialers.

[Grant Taylor]

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