Subject: Re: new 21164A 366 Mhz Alpha Computers
From: Brian Dady <[email-masked]>
To: Multiple recipients of list <[email-masked]>
Date: Sat, 27 Jan 1996 13:05:40 -0500

On Fri, 26 Jan 1996, Andrew Hofman wrote:

> >We have run EV5 chips as fast as 400 and 433Mhz in our lab.  Should
> >we announce those too?  Oops. . .
> >
> 
> The way I understand it (and I could be totally wrong), 266 and 300 MHz
> chips both roll off the same line, are produced from the same dies, etc. The
> only difference is in testing, where some are unreliable past a certain
> clock speed. These are stamped with a "266", while the small percentage that
> pass the 300 MHz test are sold for substantially more.
> 
> All that being the case, aren't you contradicting DEC's own rating for a
> given chip, as determined right at the factory? Are bigger heat sinks a
> solution to this?
> 

Speed binning is a process common to all IC's whether cpu's or drams.
Many parameters are tested, but speed is generally the paramater by which 
they are sorted.  Yes, the parts are generally the same except for the 
clock speed rating.  In some cases inoperable sections of a circuit may 
allow the chip to be used in different applications but this requires a 
change to the part number.  In some chips, redundant circuits allow them 
to be repaired to full functionality.  There is always a significantly 
higher price attached to the faster parts due to yield.  For example if a 
run of EV5's yielded 10% failing, 70% passing at 266 Mhz, and 20% passing 
at 300 Mhz, supply and demand cause the price to be adjusted accordingly 
even though they went through the same manufacturing process.  Also, more 
testing is required on the faster parts, and this raises the price even 
higher.

Power dissipation increases with clock speed, so for a large difference, 
a larger heat sink (or improved air flow) would certainly be required, 
otherwise reliability would be compromised.  Going from 266 Mhz to 300 
Mhz might not require a different heat sink, depending on the safety 
margin allowed in the 266 Mhz / heatsink design.

..enuf rambling!  
(my regular job is engineering in the ATE industry, logic & memory testers)
                                                   ///
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 Brian Dady --* Video Magic / modeller, animator ///  info != knowledge
 Santa Clara,   California / S/W developer   \\\///  knowledge != wisdom
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