I don't think it's fair (except for the not washing
the boards properly part) to say this was badly
engineered. There might have been cost issues that we
can only guess about. I worked at company that made
terminals. I asked how come there were only a few
bypass caps instead of the traditional one per chip,
and the chief engineer (who wrote The famous
Microcomputer Design book, Don Martin of Martin
Research), who definitely knew how to build things,
told me that the board would start with them all in.
Then they would be removed until the board stopped
working. Then they'd put that one back in! Seriously,
they would look at the power supply and use just
enough with a little extra margin. Costs add up, same
with poly caps, crystals (which used to cost a lot
more than they do now), etc. Maybe an engineer would
have liked to use a part, but just couldn't get it
simply because of supply condsiderations. Skilled assy
line labor used to be cheaper, too. Everyone on our
assy line knew how to use a scope, and often using one
was part of the assy process. So at that time it was
cheaper to have a tech/assy line person tweek a pot
than it was to put in a crystal.
It's my understanding that electrommagnetic deflected
vector displays take very, very high-power deflection
coils and drivers, and this is where the real money is
in these units. I don't know if the Imlac is
electrostatic or electromagnetic deflection
(electromagnetic, I suspect).
I am working on a TTL-based vector display (128x128
dots only), from a 1975ish BYTE maganize. I'm using a
Tektronix 620 display, which I can get for $15 in
clean, paint, and use condition from a local surplus
place.
--- Bob Shannon <bshannon_at_tiac.net> wrote:
> Ben Franchuk wrote:
>
> <snip>
>
> > It is not that they did not know better, that is
> all they had to work
> > with.
>
>
> Clearly you haven't looked at the Imlac schematics!
> Engineers designed
> lots of hardware
> of the same era without resorting to the kinds of
> tricks used in the
> Imlac.
>
> Did you know that each Imlac had to have RC networks
> that control its
> clocks and timing signals
> tuned by hand, for each unit? The components used
> were garden variety
> ceramic caps with very
> loose tolerances, not poly or other higher quality
> components. The issue
> here is the quality of hardware
> engineering. HP machines of the same period are
> vastly better
> engineered, as are many other machines
> from the late '60's and early 70's.
>
> To suggest that nothing better was available to the
> engineering team at
> Imlac is laughable at best.
>
> >
> > Mind you cost cutting often did not help any
> computer product.The real
> > problem
> > is the Imlac is VECTOR display. Finding a new CRT
> would be a problem
> > with the
> > original design. A raster scan display design
> could be used but then you
> > need to buffer the display correctly to have
> unrefreshed data fade off
> > the screen.
>
>
> The vector display has nothing to do with the design
> quality whatsoever!
>
> What makes you say something like this Ben? For
> what the Imlac did,
> when it did it, VECTOR was
> FAR SUPERIOR to raster displays.
>
> Please note, the Imlac had a 1024 by 1024
> addressable display, prior to
> 1970. This greatly exceeds what
> was possible with raster graphics at the time, and
> the Imlac was
> designed for calligraphic applications where
> its short vectors made for a mugh higher quality
> display than a
> pixellated raster display of the same resolution
> would have. There is also the fact that
> manipulating raster display is
> far more computationally intensive than
> manipulating a vector display list. The Imlac CPU
> would not be well
> suited for raster graphics at all, but its more
> than sufficient for its intended use.
>
> The problems with the Imlac are issues of
> engineering quality, like the
> total lack of decoupling capacitors, poor
> grounding, and poor logic design. This is also
> reflected in the
> manufacturing of early units in the failue to wash
> the
> etchant off the boards (many Imlac boards now have
> fuzzy green etches,
> or no remaining etches at all) and poor metal
> preperation prior to
> painting, and the fact that the design was very
> quickly repackaged as
> the PDS-1D's.
>
> The CRT used in the Imlac was common enough in its
> day, and that same
> tube was also used in much higher quality products
> as well.
>
> The last comment about the display refesh is hard to
> understand. The
> Imlac does not use a storage tube, and it
> must keep the display refreshed in the same way as
> any raster graphics
> display does. I'm not at all sure I understand your
> point here, can you
> expand on this point?
>
> If your suggesting re-implementing the Imlac with a
> raster display, this
> is totally impractical. My ReImlac project will use
> a real vector
> display, as that is the only way to duplicate the
> capabilities of the
> original machine. Remember, the Imlac does not have
> jagged vectors even
> when drawing at any angle. To try to do this on a
> raster display would
> reqire a resolution far far greater than 1024 by
> 1024. The anti-alising
> along would take more logic than the full original
> machine does.
>
> On the other hand, a Wells Gardner vector monitor is
> more than able to
> display the vector video from an Imlac exactly the
> way a real Imlac
> does. So will most small oscilloscopes, or even a
> modified TV monitor.
> Small vector display monitors are fairly common on
> eBay at very
> affordable prices. So whats the problem with a
> vector display?
>
> To be true to the original, I'm sticking with a true
> vector display.
> After all, I'm quite addicted to vector (and point
> plot) displays, and
> this was my main attraction to the Imlac. If this
> were replaced by a
> raster display, you might as well run a software
> emulator and not bother
> re-implementing the Imlac in hardware at all.
>
> The vector display of the Imlac is a thing of beauty
> and is a huge part
> of what makes an Imlac so unique. To call this
> "...the real problem..."
> is heracy!
>
>
>
>
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Received on Sat Sep 14 2002 - 14:28:00 BST