jamesd@lakesys.UUCP (James Dicke) (10/04/88)
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. I want to stock a 2.5 MEG board but the ram chip prices are just too high (about $600 per meg new). If you have any and are willing to sell or have a complete full ramboard not being used please contact me. Thank you. James Dicke (414) 462-8973
tif@cpe.UUCP (10/05/88)
Written 11:02 pm Oct 3, 1988 by lakesys.UUCP!jamesd in cpe:comp.unix.xenix >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. Paul Chamberlain Computer Product Engineering, Tandy Corp. {convex,killer}!ninja!cpe!tif
debra@alice.UUCP (Paul De Bra) (10/06/88)
In article <6800049@cpe> tif@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. |-------------------------------------------------------------------------- |Paul De Bra | I am completely surrounded by giant bugs ! | |debra@research.att.com | There's millions of them, all over this code! | |uunet!research!debra | Beam me up quickly...Please... | |--------------------------------------------------------------------------
jbayer@ispi.UUCP (id for use with uunet/usenet) (10/07/88)
In article <8266@alice.UUCP>, debra@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.stacy@mcl.UUCP (Stacy L. Millions) (10/09/88)
In article <6800049@cpe>, tif@cpe.UUCP writes: > > Written 11:02 pm Oct 3, 1988 by lakesys.UUCP!jamesd in cpe:comp.unix.xenix > >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. I have a 12MHz 0ws 68000 machine from a few years back that uses 150ns DRAM, the manufacturer admitted that they were pushing the chips past specs, but also said they had a low failure rate doing it. I missed the original article, are you looking for more RAM to put on the mother board or on an expansion card? If it is going on an expansion card than the fastest speed you have to worry about is 10 MHz. I am not aware of any systems that go faster than 10MHz on the I/O bus, even at 10MHz alot of cards fail. -stacy -- "He to whom the early bird runs best learns wisdom and patience! ... I can never remember proverbs" - Charlie Brown S. L. Millions ..!tmsoft!mcl!stacy