IBM 2260 acoustic delay line
phb.hfx at gmail.com
Sun Dec 13 00:03:20 CST 2015
On 2015-12-12 11:37 PM, William Donzelli wrote:
> The IBM 2848, the control unit for the 2260 terminals, contained
> mercury (!) delay line for the video memory. There may have been some
> compensation for the transmission to the terminal, but I have have not
> seen the technical details - I think it was not a concern, probably.
> Line loss is really not a problem. It might have been if the lines
> were miles long, but in typical installations, that was not anywhere
> near a problem.
> As for speed - not an issue for basically baseband video.
> On Sat, Dec 12, 2015 at 10:13 PM, Eric Christopherson
> <echristopherson at gmail.com> wrote:
>> On Sat, Dec 12, 2015, Jon Elson wrote (in the big top posting thread):
>>> On 12/12/2015 07:22 AM, Mike wrote:
>>>> The one question I do have for the older gentlemen on here is what in the
>>>> world did the computers without a screen to look at do? Now I know about
>>>> the tape, cassette tape's and even the paper with the hole punches in them
>>>> but what kind of applications were they use for? Mathematics or? ? ?
>>> Later they got some
>>> IBM 2260's, which were Zenith 9" TV sets and a keyboard connected to an
>>> interface box in the machine room. Very primitive, but very interactive,
>>> great for quick program editing and submission.
>> I'm reading about those terminals and find it just fascinating how they
>> used acoustic delay line memory to remember the pixels. But I have lots
>> of questions:
>> 1. Did the cables connecting the 2260s to the display controller
>> actually contain the delay lines themselves, over the whole length; or
>> were the delay lines just inside the controller and then some electronic
>> signal was sent out to the terminals?
>> 2. I would think that the wave travelling along the delay line would
>> weaken over time. How was it refreshed?
>> 3. What kind of speed could be acheived, and did this depend on the
>> number of connected terminals?
>> Eric Christopherson
I just read the section of the 2260 and 2848 Theory of Operation
Manual, found on bit savers, regarding the delay lines and they are not
mercury delay lines, in fact I do not believe that IBM ever used mercury
While I started as a service rep too late for this display system I did
get to work on other machines that used delay lines just like the one
pictured in this manual, like the 1260 "electronic" proof machine and
test scoring machines. The easiest way to think of the delay line is it
is like a very long shift register. At the start of the delay line an
electromagnet introduces a pulse into the wire, using a
magnetostrictive effect, that will travel the length of the wire and is
sensed by a transducer at the other end. In between the ends you have
a solid state register to extract and insert data into the stream. The
manual also notes that NRZ encoding is used on the delay line. The
delay lines are 5.5545ms long and the bit rate of the delay line (500ns)
which would give you a little over 11K bit of storage. The bit rate of a
single delay line was not fast enough to keep up with the display so two
delay lines are interleaved to provide a 250ns bit rate. The delay
lines used as the display buffer contain the serialized data that would
become the video signal at the CRT. If you are really interested in
how these delay lines work the relevant material starts at on page
2-29 (pdf page 73).
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