I checked the Bell Labs Eng & Sci history and I have some corrections
to what I wrote:
>> they got University of Chicago to split the cost with them
>> fifty/fifty to install centrex;
The goal of Centrex was more than Direct Inward Dialing. There were
two other goals as well around 1960 for Centrex:
- Outward dialing with direct billing to extension
- Encouragement of use of new DDD network.
As mentioned, PBX operators served as a gatekeeper for long distance
calls since there was no way to charge back to an individual
extension. Centrex included extension identification and billing and
it was a key part of it. This way extensions could dial out directly
and get billed back. Originally this was done with CAMA (ONI) but
later regular AMA with ANI.
With DDD being implemented, the Bell System wanted callers to get away
from "Get me Joe Smith at ABC Company, Kansas City" to "get me
311-555-2368" or better still, dialing it himself. By dialing
extensions directly, people would get used to dialing for themselves
and not using an operator. Likewise for outward calls.
> Somehow the dial system could decode allowable exchanges and reject
> distant ones. People were allowed to dial out to the city and
> adjacent suburbs only, any other 7 digit call that generated a message
> unit charge was not allowed and no 1+ calls were allowed.
> Maybe the trunks were restricted at the CO by special arrangement.
The Bell history said this toll restriction was done by panel or
#1xbar at the Central office; that is, the trunks could only make
local calls. This was introduced in 1953.
> In other words, in the old days, until probably around 1975, a manual
> cord switchboard was cheaper to build than the equivalent dial system
> to replace it. After 1975, electronics made dial equipment cheaper.
> The huge drop in the cost of electronics and concurrent growth in
> power (look at the cost of logic and memory chips in 1975 vs today)
> enabled automatic systems to be everywhere
According to the history, the newest 608 boards were still being
shipped in 1968. (My high school got a 555 in 1968, I don't know if
it was new or reconditioned.) I'd love to know when the last cord
boards of various types were made. (When did the last conventinal 500
set come out?)
My guess is that by 1980-1985 cord switchboards were rapidly replaced
by electronic gear, either rented from Bell or bought privately. I
wished some of the big ones (or at least the jack faces) could've been
salvaged somehow but they were awfully big and heavy. Small 555s seem
to be around. Even small installations required Bell maintenance from
time to time, too.
The history details developments of electronic PBXs. This took time
and did not come easy, especially for small installations where the
high cost of electronic common control would be spread among few
stations and thus not be economical. Also, I suspect Bell had a large
inventory of traditional cord boards and wanted them used as well so
the newest style PBXs and console-switchboards were priced at a
premium. (IBM did the same with older computers).
> [TELECOM Digest Editor's Note: When there was any need of repair
> service, for example on the board itself, a repair person was there
> in usually 30 minutes.
I'm sure there was at least one, probably more, Bell employees at your
site full time to handle repairs and extension change orders.
> Finally he was finished, put his tools back in his holster and turned
> to leave, but he paused, looked at me and said, "You know, if I
> mentioned this to Mrs. Parsons (our chief operator) you would get
> fired -- be out on your ass! -- as soon as she heard about it."
I think "Mr. Hamilton" saved you. I wonder what the repairman had to
Our little PBX in school had a big red sticker "LIQUIDS SPILLED ON THE
SWITCHBOARD WILL DISRUPT YOUR SERVICE".
In my high school we had a Teletype for computer time sharing. It
failed and the repairman (from Bell whom we rented the TTY from at
$100/month) found lots of raisons gumming up the works. One kid liked
to eat them while working. The repairman said any future repairs of
that nature would be billed. We teased the kid forever with that.
The school system eventually bought its own TTYs. The Bell ones had
the built in equipment ASR (buttons on the side, automatic
connection). Our new ones had an external modem and DAA box and plain
phone with a 2-way switch. We also had offline Teletypes. We found
that offline units also had a modem in them and a way to connect them
to an idle phone line (and not using any DAA). The School District
didn't like this since (1) it tied up phone lines not meant for that
purpose and (2) it violated the rules.
One rich kid rented his own Teletype from Bell for a month. We were
When I got my first home PC, I realized I had a device that did
everything our old Teletypes did, only at a faster speed (2400 vs
110), and here it was in my home. Actually, I didn't need to dial up
to anything since GW-BASIC was included in the machine. I avoided
eating raisons while on the PC.
[TELECOM Digest Editor's Note: You referred to him as 'Mr. Hamilton'
but around Chicago he was known as 'Mr. Green'. For example, a
lawyer might go into court and ask for a continuance on the case or
the judge might grant a continuance because 'Mr. Green has not yet
had a chance to give his testimony.' Or if 'Mr. Green' had been in
judge's chambers or the lawyer's office, then often-times the judge
or the prosecutor and other lawyers would decide it is 'in the best
interest of justice' to dismiss the case. PAT]