Ram chips wanted!

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In article <8266 at alice.UUCP>, debra at alice.UUCP (Paul De Bra) writes:
. 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)

This table is fine if you are using normal DRAM, but there are other types
of memory available.  For instance, there is static RAM, static column cache
RAM, and other more esoteric types which are only now starting to come into
the marketplace.  These other types usually run faster than DRAMs, although
they have other drawbacks such as greater power requirements, less chip
density (necessitating more chips for the same amount of memory), possibly
greater support requirements, etc.


Jonathan Bayer
Intelligent Software Products, Inc.