11 Sep
2017
11 Sep
'17
10:20 p.m.
On 9/9/17, Lawrence Stewart <stewart(a)serissa.com> wrote:
What, you didn’t like IBM 2741 terminals that
mechanically locked the
keyboard?
In the business world, these terminals were typically half-duplex and
attached 4 or 8 (or more) to a control unit that communicated with the
computer using bisynch protocol. It's like a telephone party
line--only one terminal can communicate with the computer at a time.
The remainder were locked out. [Note that Ethernet works pretty much
the same way.] If you wanted to talk to the computer, you pressed the
"Request" key. This caused the control unit to send an interrupt to
the computer, which in due course would then unlock your terminal and
talk to you. This works out OK for transaction processing, but it's
not a good fit for interactive time-sharing.
-Paul W.