The other day I was touring one of the HP support labs where they have a
LARGE collection of HW that is used for reproducing customer problems.
(I was there to see some of the new Generation 9 machines that are coming
out...) ANYWAY, they pretty much have all of the HW that they have
support contracts for... and that generate enough questions to reserve
floor space for the HW.
Guess what still has floor space? A DEC 7000 and Vax 6000. Not a
PDP-7, but still enjoyed seeing them...and knowing that enough places are
still using them to cause HP to reserve floor space for them in the
lab...(proof, as always, is in the pictures :
http://s1290.photobucket.com/user/theearlsquirrel/library/ )
Earl the Squirrel
[John Foust, quoting me]
>> I don't understand why this technique was used. Perhaps it's
>> easier/cheaper to produce a nonsmooth surface made of a uniform
>> material than to produce a smooth surface of a nonuniform material?
> I'm not quite sure what you mean here.
The goal is changes in reflectivity on a fairly small scale.
There's no reason in principle this couldn't be done with a smooth
surface by making the surface not all the same material. (A
larger-scale example of this is ink on paper: inked paper reflects less
light than un-inked paper does.) I was speculating that, on the scales
of interest here, it's easier/cheaper to produce a non-smooth surface
of a uniform material (how pressed CDs are actually made) than to
produce a smooth surface of a nonuniform material (the alternative).
> Wikipedia has an explanation of the process:
> http://en.wikipedia.org/wiki/Compact_Disc_manufacturing
Yes, but it does not discuss why that process was chosen over various
alternatives.
>> Is it possible that it's clear only in visible light, with some sort
>> of reflective layer present in the (infrared, IIRC) wavelengths
>> used?
> But as you mentioned, detection normally uses the phase shift, and
> that's dependent on the frequency of the light.
Yes, but I think the light normally used for CD reading is outside the
visible range. This raises the possibility that the disc might be
clear in the visible range but not in the range used for reading.
Your experience trying to read it argues against that, though. Oh
well, it was a nice theory while it lasted.
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Folks,
Thanks to building reductions we're having to offload all our old VAX kit
and I'd much rather see it go to someone who can use them, even as spares.
There's also a load of UNIBUS and QBUS spares, too many to list.
Big stuff:
VAX 7710, various processors + memory
AlphaServer GS60e
Possibly VAX 6610
Less big stuff:
Alpha 2100 + spares
Alpha 2000
Alpha 800
Alpha 1000 x3
AlphaStation 2xx x4 (spares only)
2 MicroVAX 2000
Various VAXstations, 3100s etc + spares
Several BA415 VAXen, 3400/3800/4200/4300
VAXstation 4000s
Possibly an Alpha1200 and DS20 (big box version)
Collection only, obviously these things are HEAVY.
Cheers,
--
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk
At 05:57 PM 11/17/2014, Don Hills wrote:
>I think you're actually more likely to be able to read it in modern drives,
>which are designed to handle lower reflectivity as found on burnt CD-R and
>CD-R/W discs.
So far, no luck on that front. I think it would require a tweak in firmware.
At 06:07 PM 11/17/2014, drlegendre . wrote:
>Slap a layer of Mylar on the back and give it a shot..? Might even work
>with something of lower reflectivity, like white paper..
Adding a reflective layer to the back was a first and obvious idea,
but upon deeper reflection I don't think it's the right answer.
The pits receive the sputtered aluminum. If adding a backing
layer was the answer, you'd think CD-ROMs would've been made
that way in the first place, as it's easier. It's not a matter
of boosting reflectivity in general, it's about accentuating the
difference between pits and lands.
(I tried Krylon "Looking Glass" spray paint on a couple test discs.
Although this paint does a wonderful job of mirror-izing glass,
it turns out more gray on plastic.)
If the anecdote about early CD drives being able to read non-aluminized
discs is true (and I believe the stories) then it would seem the answer
would be to find a drive that used the old Phillips read heads and
somehow ask it to dump a raw image of the bits it finds, in order
to allow another system to interpret the image. High Sierra wasn't
adopted until late 1986, and ISO-9660 after that.
The CM100 apparently only works on PC and XT era hardware. I saw
mentions on the web that even a 25 Mhz PC is incompatible.
At 02:51 PM 11/17/2014, Mouse wrote:
>I don't understand why this technique was used. Perhaps it's
>easier/cheaper to produce a nonsmooth surface made of a uniform
>material than to produce a smooth surface of a nonuniform material?
I'm not quite sure what you mean here.
Wikipedia has an explanation of the process:
http://en.wikipedia.org/wiki/Compact_Disc_manufacturing
>Is it possible that it's clear only in visible light, with some sort of
>reflective layer present in the (infrared, IIRC) wavelengths used?
The pits surface is normally aluminized and then covered with
some sort of acrylic or lacquer. I too wondered if there's not some
optical characteristic of that boundary that could work like
aluminum. But as you mentioned, detection normally uses the
phase shift, and that's dependent on the frequency of the light.
You'd need to develop an entirely different optical path.
- John
> From: Ben Sinclair
> what is the best way to connect the wire-wrap jumpers? I've never
> actually wire wrapped anything, but is that what I should do?
Well, I use wire-wrap, but anything that makes a good connection and doesn't
get in the way (of other cards, etc) is fine, really. Don't feel you have to
use wire-wrap, or anything.
If you want to wire-wrap, there are two ways to go. They used to make manual
tools for wrapping the wire, but I've never used those; I learned with a gun.
Those are available on eBay now for relatively cheap, since wire-wrap is now
more or less obsolete (if you're slightly patient - I paid $25 for a kit
containing two guns, a bunch of different tips for different gauge wire,
several packages of pre-stripped wires, several of the strippers that cut the
wire and strip the right amount, and some un-wrap tools - a great deal :-);
that's the way I'd go.
They are pretty easy to use; the only real trick is to learn how to apply just
the right amount of up-down force while doing the wrap. Too much up, and you
tend to pull the gun up as it wraps, and you don't get a nice tight wrap. Too
much down, and you get an ugly ball at the bottom of the post as the wrap
winds around itself. The trick is to try and hold the gun neutrally weighted,
and as it wraps let it push _itself_ up the pin, producing a nice tight wrap.
And of course you can do test wraps, and undo them if they come out looking
bad. It doesn't take long to get reasonably good with it.
Noel
> From: shadoooo
> still I'm very interested to unibus (possibly qbus) boards.
Actually, if someone in the UK wanted to be rewarded with a modest fee,
I'd happily pay for them to go pick up all the cards and ship them to
me (in the USA). Any I don't need I'd be happy to pass along.
No matter what, they shouldn't go in the dumpster/recycle, if at all possible!
Noel
I've come across a program called "geepro" for burning EPROMs under Linux,
but I've yet to identify a known-good programmer. Could someone please
recommend one? Geepro's documentation says that it supports the Willem
4.0. On Ebay I see the "GQ-4X" which is claimed to be a "Willem
Universal". Will that work?
--
David Griffith
dgriffi at cs.csubak.edu
> As I understand it, the depth of the pits are about a fifth of the
> wavelength of the light used to read them, so the detector sees a
> phase shift.
I thought the pits were, in theory, 1/4 wavelength deep, so that the
reflection from the pit is 180 degrees out of phase with the reflection
>from the surrounding area, producing destructive interference (ie,
manifesting as a drop in reflectivity). Of course, .25 is about .2....
I don't understand why this technique was used. Perhaps it's
easier/cheaper to produce a nonsmooth surface made of a uniform
material than to produce a smooth surface of a nonuniform material?
(That's the other way I'd expect to produce reflectivity variations.)
Is it possible that it's clear only in visible light, with some sort of
reflective layer present in the (infrared, IIRC) wavelengths used?
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