[RC5] Golomb Rulers (was "sexy" projects)

Joe Zbiciak j-zbiciak1 at ti.com
Tue Mar 3 20:49:47 EST 1998


'Thomas Womack' said previously:

| I've read about those; I haven't had the chance to do VLSI design myself,
| but I checked the pricing fairly carefully before posting. Yes, it's
| possible to do the design for free - but what gets you, and what I can see
| no way to avoid, are fabrication costs.

MOSIS is pretty expensive for large quantities.  I'm sure you could
cut a pretty good deal, though, if you wanted an even number of wafer's 
worth of a chip.  (Typically, MOSIS wafers have many different chips on
them, so most of the $ probably goes into mask generation/verification 
for each of the different chips.  With only one type of chip on the 
whole wafer, I imagine that portion of the cost goes down.)

Imagine fabricating a Pentium (~120 sq mm device) at MOSIS.  They charge
$920 / sq mm for the first 25 parts, and $690 / sq mm for each additional
batch of 25.  This translates to $3900 - $5200 a chip!  And that's for an
MMX Pentium in 0.35 micro technology.  Obviously, the cost of the fab for
short runs is *much* higher than it would be for more sizable runs.

When you consider that an MMX Pentium probably sells for 1/30th of this
price, and is probably fabbed for less still, it becomes apparent that
the cost target originally proposed only makes sense for large runs of
such a DES super-cracking device.


| Doing it three orders of magnitude
| faster for a factor of fifty less cost is impressive - but you need another
| two orders of magnitude cost reduction to make hardware approaches at all
| cost-effective.

I will say that you're right, $10,000 for a full-custom device which
cracks a DES encoded message in "a few minutes" is probably far
fetched.  In quantity, though, I would say not.  Perhaps add a factor
of 2 or so.

Regards,

--Joe

-- 
 +----------- Joseph Zbiciak ----------+  Eliminate idle cycles!
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