🚀 go-pugleaf

amc@ai.wustl.edu (Adam M. Costello) writes:

>In article <1990Sep1.133213.6765@jarvis.csri.toronto.edu> leblanc@eecg.toronto.edu (Marcel LeBlanc) writes:
>>much rather pay for an extra 512K of RAM!  The RAM costs less than the ROM,
>>and has much faster access times (especially the SC RAM).  Remember that all

>RAM costs less than ROM?  I'm surprised.  How much less?  RAM is faster than
>ROM?  I'm surprised.  How much faster?  It seems to me that ROM must be simpler
>than RAM, so it should be easier and cheaper to make it faster.  Why isn't it?

"Why" is a good question, but I don't have the answer (maybe somebody else
will post an answer).  The best guess that I can offer is that ROM must be
custom produced.  Each ROM must have a separate custom mask (probably
metalization), and is only produced in relatively small quantities, whereas
RAM is mass produced at commodity prices.  However, I do know that my
company can buy 1Mb EPROMs (more expensive than ROMs if you have high enough
volumes to recover the ROM NRE costs) for ~$10 each (1000 quantity) with
200ns access times.  1Mb DRAMs can be bought for ~$6-$7 with <100ns access
time (so <200ns cycle time).

This is probably why Commodore distibutes the "SetCPU" program to copy the
Kickstart ROM to SC RAM even on the A3000 (note the SC DRAM has a best cycle
time below 40ns).  If somebody has more info, please post.

>AMC

Marcel A. LeBlanc  --  Electrical Engg Computer Group, Univ. of Toronto
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