see below, plz.
Dick
----- Original Message -----
From: "Davison, Lee" <Lee.Davison_at_merlincommunications.com>
To: <classiccmp_at_classiccmp.org>
Sent: Saturday, May 12, 2001 2:24 AM
Subject: RE: Converting TTL monitor to Analog
>
> well, the boxes with intended for multidrop or high-bandwidth
> serialized
> compressed digital video are not on topic for this thread. We're
> trying to
> establish whether there really are digital interfaces to the old
> (get
> it...classic computers... over 10-years old ... using interfaces of
> that era)
>
> Sorry but digital video wasn't new when I started in broadcasting in the early
80s.
> The BBC used digital for distribution and moving captions were stored
digitally
> (remember the translucent spinning globe? Megabytes of data compressed into
> a 600kbyte EPROM store).
>
Nothing digital was new back in the early '80's. However, workstations in the
early '80's had video DAC outputs that operated at 275 MHz (and cost about $3
per MHz) and that stuff didn't go in the monitor, which, IIRC, cost on the order
of $12k for a useable (analog) 19" type. Generally speaking, those weren't
multi-sync type monitors, either.
Back then, all the technology was in place, but the market was so limited none
of the economies of scale that later came into play to make these things
affordable were available.
>
In the early '80's, a 600KB EPROM store would have cost as much as a
medium-priced VAX. I remember paying $120 each for 2732's in the early '80's.
That was 4KB with 450ns access time.
>
> So you'be suggesting 5 bnc's? three for video and two for sync
> signals?
>
> No, one.
>
While it was common to put negative-going sync on positive-going analog video,
and while monitors with the necessary video bandwidth to display 1kx768
(nominally) pixels at considerable resolution (6 bits/color, using TRW
Triple-DAC's costing close to $1k in "production" quantity) This wasn't done
with digital signals on the monitors I saw. Even with common ECL, the bandwidth
just wasn't there to produce the necessary number of bits within the necessary
amount of time to produce a 60 (or even 50) Hz vertical rate with the necessary
number of horizontal sweeps and pixels per sweep. The "fast" DACs of the time
were commonly of the 70ns variety. The "ultra-fast" ones would operate in a
compromised mode, maybe to 4-bit resulution, at an 80 MHz conversion rate per
DAC. That would have required an overall bandwidth (via a single BNC) on the
order of 250 MHz, and most of the logic capable of transferring that sort of
bandwidth was used in really expensive hardware, like military supercomputers.
PC enthusiasts normally didn't spend that sort of dough on their video systems.
>
> Lee.
>
>
>
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Received on Sat May 12 2001 - 09:18:04 BST