🚀 go-pugleaf

>I've heard that crap from several people. Actually you could find out how
>fast a simm can run but you have no guaranty that it could run that
>fast continuously (assuming you pick the high speed).
>Anyone done that is playing with fire, the 70nS part may work fantastic
>as a 60nS for 99.9% of the time then oooppss!
>As far as the manufacturers, too funny to comment.
>
>Michel Catudal
>Proud user of OS/2 Warp
>
Short Answer:  If you want to run 60 and 70 ns parts in the same machine, treat them all 
like 70 ns parts.

Long Answer:  There are three phases of part production for timing graded parts such as 
DRAMs:

1)  Early Production.  In this case, they test the parts and determine which are faster 
parts and which are slower parts and mark them accordingly.  (Speed Variations occur 
because of variations in the IC fabrication processing).  If you purchase slower parts in 
this phase, they have been tested as _NOT_ being fast.  70 ns parts in this phase _ARE_ 
70 ns parts.

2)  Early-Mid Production.  In this phase, the company has committed to delivering two 
grades of parts, but their process has improved to the point that all that they put out 
are the faster parts.  They will mark some as slower because they have promised to sell 
two part types at two different speed grades.  If you purchase slower parts in this 
phase, they are just as fast as the fast parts.  How can you tell whether this is the 
case?  You can't.  Companies don't want to operate in this mode too long because they 
don't make as much money (it's like selling Premium gasoline at Regular prices).

3)  Mature / Late Production.  In this phase, the company simply stops selling the slower 
parts.  Companies like to switch to this mode as soon as possible.

The timing of a digital machine (such as your computer) depends on:

Speed of memory
Speed of other parts associated with the memory access path
Loading of the data and address busses (a function of how many cards and SIMMS are in the 
machine  More stuff => Slower Logic)
Voltage of the machine (Higher Voltage => Faster Logic)
Temperature of the machine (Higher Temperature => [typically] Faster Logic)
Other Assorted Factors (jokingly called "Phase of the Moon").

You might get by with using slower parts at higher speeds.  This could be because you 
have faster other logic than advertized, your machine might be cooler than the maximum 
temperature specification, and the electrical loads on the address and data busses might 
be lower than the worst case.  You might get lucky, and have it dependable.  I personally 
find, however, that a computer crash _ALWAYS_ takes me more time to recover from than I 
would save by having marginally faster memory access.

Hope this helps clarify things. - k.