Ram chips wanted!
Paul De Bra
debra at alice.UUCP
Thu Oct 6 08:17:20 AEST 1988
In article <6800049 at cpe> tif at cpe.UUCP writes:
>>I need memory chips for my 12MHz 286 so I can run Xenix better. The chips I
>>am looking for are 256k 80ns DRAM's.
>
>Obviously you can buy whatever you want but isn't 80ns faster than necessary
>for a 12MHz machine? Seems like we put 100ns in our 16MHz 386's.
>
How fast rams have to be to work at a given clock-speed depends on how much
time they get from the CPU, and how much time the surrounding hardware (mmu
and such) already consume. A rough estimate is that the surrounding hardware
takes 1 clock tick and the memory 1 or 2 clock ticks (depending on 0 or 1 wait
state). The reason that this is a useful estimate is that machines with faster
clocks use faster mmu's too. It boils down to the following table:
clock 0-wait 1-wait
6Mhz 165ns 250ns
8Mhz 125ns 185ns
10Mhz 100ns 150ns
12Mhz 83ns 125ns
16Mhz 62ns 94ns
20Mhz 50ns 75ns
25Mhz 40ns 60ns
This is only a ROUGH estimate, but it shows that a 12Mhz AT with 0 wait states
needs 80ns rams, and if a 16Mhz machine is using 100ns rams that means it is
running with at least 1 wait state (not accounting for a possible cache)
Paul.
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|Paul De Bra | I am completely surrounded by giant bugs ! |
|debra at research.att.com | There's millions of them, all over this code! |
|uunet!research!debra | Beam me up quickly...Please... |
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