23 Jan
2018
23 Jan
'18
10:35 a.m.
A few notes:
The experimental Ethernet speed was in fact 2.94 MHz: It's the Alto clock
divided by 2.
The Alto based printer was called "SLOT" -- Scanning Laser Output
Terminal. It was plugged into the Alto backplane and presented itself as a
hardware peripheral controlled by microcode (as was the case for all Alto
I/O). It was an Alto task, of course.
The vampire tap transceiver used RG-8 cable originally. That's before they
added the lines around the cable and added additional shielding.
The XGP was used at the Stanford AI Lab and was, as mentioned early, a dry
process. And it did use a roll of paper.
23 Jan
23 Jan
11:15 a.m.
On Jan 23, 2018, at 1:35 PM, Mark Kahrs via cctech
<cctech at classiccmp.org> wrote:
A few notes:
...
The vampire tap transceiver used RG-8 cable originally. That's before they
added the lines around the cable and added additional shielding.
The cable spec given in the Ethernet standard doesn't mention additional shielding.
It does differ from RG-8 in that it calls for foam dielectric and a higher velocity factor
(0.77 rather than 0.66). Another common difference (not required by the spec) is that
RG-8 is polyethylene while Ethernet coax is usually PTFE.
paul
1:17 p.m.
On Tue, Jan 23, 2018 at 11:15 AM, Paul Koning via cctalk
<cctalk at classiccmp.org> wrote:
The cable spec given in the Ethernet standard doesn't mention additional shielding.
It does differ from RG-8 in that it calls for foam dielectric and a higher velocity factor
(0.77 rather than 0.66). Another common difference (not required by the spec) is that
RG-8 is polyethylene while Ethernet coax is usually PTFE.
FWIW, here is a spec sheet for Belden 89880 Thicknet 10BASE5 cable,
which apparently DEC used for their part number 17-00324-00 cable.
https://catalog.belden.com/techdata/EN/89880_techdata.pdf
It does mention a Nominal Velocity of Propagation (VP) of 78%, and
Ring-band stripes every 2.5 meters to aid users in tap placement,
among other specifications.
You could buy a 1000-ft spool on eBay for only $480, vs $9,818 at Mouser.
1:22 p.m.
On Jan 23, 2018, at 4:17 PM, Glen Slick via cctalk
<cctalk at classiccmp.org> wrote:
On Tue, Jan 23, 2018 at 11:15 AM, Paul Koning via cctalk
<cctalk at classiccmp.org> wrote:
Yes, that looks like the stuff. A smoky orange color due to the translucent jacket. I
once saw at DEC a run of prototype cable, which was bright yellow with black stripes.
Perhaps polyethylene jacket, which would explain why it was changed before becoming a
product -- that was right around the time when the "plenum rated" cable specs
were appearing.
paul
The cable spec given in the Ethernet standard doesn't mention additional shielding.
It does differ from RG-8 in that it calls for foam dielectric and a higher velocity factor
(0.77 rather than 0.66). Another common difference (not required by the spec) is that
RG-8 is polyethylene while Ethernet coax is usually PTFE.
FWIW, here is a spec sheet for Belden 89880 Thicknet 10BASE5 cable,
which apparently DEC used for their part number 17-00324-00 cable.
https://catalog.belden.com/techdata/EN/89880_techdata.pdf
<https://catalog.belden.com/techdata/EN/89880_techdata.pdf> 
11:24 a.m.
On Tue, Jan 23, 2018 at 10:35 AM, Mark Kahrs via cctech <
cctech at classiccmp.org> wrote:
A few notes:
The experimental Ethernet speed was in fact 2.94 MHz: It's the Alto clock
divided by 2.
The Alto based printer was called "SLOT" -- Scanning Laser Output
Terminal. It was plugged into the Alto backplane and presented itself as a
hardware peripheral controlled by microcode (as was the case for all Alto
I/O). It was an Alto task, of course.
There was also the later Orbit controller, which talked to a number of ROS
(Raster Output Scanner) devices, including the Dover. The Orbit controlled
the ROS and the printer and had special hardware + microcode to assist in
the generation of raster bands (16x4096 pixels) for imaging. This allowed
the Alto to keep up with the Dover (which was approximately 1 page/second)
in real time while generating 384dpi output.
(Incidentally, not all Alto I/O was implemented as hardware + microcode --
just the high-bandwidth stuff; there was memory-mapped hardware at the top
of the address space for keyboard/keyset/mouse and various other devices.)
Also: The latest version of ContrAlto (
https://github.com/livingcomputermuseum/ContrAlto) emulates the Orbit and
Dover ROS in case anyone's itching to print some PRESS files :). Bitsavers
has a set of disks I put together with Spruce (one of a number of
Alto-based print servers) if you want to play around with it.
- Josh
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participants (4)
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derschjo＠gmail.com -
glen.slick＠gmail.com -
mark.kahrs＠gmail.com -
paulkoning＠comcast.net