tmkk@uiuc.edu (K. Khan) (06/25/91)
I have been trying to upgrade a Dell system 200 for a friend. She bought the machine used, and has no owners manual or other documentation. So, I called Dell's customer service number and found out that I could install up to 4 1M SIMMs into the slots on the motherboard. My friend went out and purchased 4 1Mb 70ns SIMMs (the original 256K SIMMs were 120ns, but the place she ordered from did not have anything slower than the 70ns chips). The chips arrived, we plugged them in, and NOTHING. The machine does not recognize them. Another call to Dell confirmed that the system 200 does accept 1Mb SIMMs and that there are no DIP switches or jumpers which need to be changed. He suggested that the 70ns chips were, and this is a quote, "too fast." This sharply contradicts my understanding of RAM accesss times - it's like saying a car with a top speed of 200 MPH is "too fast" to be driven on a highway with a speed limit of 55 MPH. The speed rating on a RAM chip represents the FASTEST rate at which the data can be accessed; slower access rates are also OK, you just can't access any faster than the rated speed without problems. Isn't that right? So, tell me the truth: is it possible for a RAM chip to be too fast for a particular machine, or was this Dell technician merely an intense bonehead? Oh, and if you can help with the original problem of getting 4 1Mb SIMMs to work in a Dell system 200, I'd appreciate that too! ;-)
hdrw@ibmpcug.co.uk (Howard Winter) (06/26/91)
[about whether DRAM chips with a faster speed rating than needed should work] You are right, he is wrong - the speed rating is related to the time the chip needs for its output data to stabilise after the 'Read' signal is asserted (for the purists - this is s Gross Simplification). Having chips that are too fast just means they sit around with valid data for longer - They should work perfectly. The only other parameter which could affect things is how often they need to be refreshed, and I can't imagine that's going to be a problem - the refresh allowance is normally very generous - otherwise unreliable memory would result. Also this doesn't sound like your problem. Power requirement normally goes up with faster chips, but unless the PSU is almost at its limit in the original setup, that's unlikely to be it either. BUT there are two modes of accessing SIMMs - and this is where I can't remember the details, but I think its page mode and interleave mode. Not all DRAMs can do both, I think, so it could be yours are being driven by the Dell in a mode they aren't designed to use. Someone else can probably fill in the details of this - sorry I can't do so. Good luck Howard. -- Automatic Disclaimer: The views expressed above are those of the author alone and may not represent the views of the IBM PC User Group. -- hdrw@ibmpcug.Co.UK Howard Winter 0W21' 51N43'
mig@cunixa.cc.columbia.edu (Meir) (06/26/91)
I know nothing about your Dell 2000, but you need to make sure that it will take 4 meg SIMMS. Maybe it will only take 1 MEG and lower. Then, go into setup and manually enter the amount of memory.... I think that too fast memory is not the problem, here. * * * * * * ====================== Meir Green * * * * * * ====================== (Internet) mig@cunixb.cc.columbia.edu * * * * * * ====================== meir@msb.com mig@asteroids.cs.columbia.edu * * * * * * ====================== (Amateur Radio) N2JPG
dwgordon@matt.ksu.ksu.edu (Dwight W. Gordon) (06/26/91)
hdrw@ibmpcug.co.uk (Howard Winter) writes: >[about whether DRAM chips with a faster speed rating than needed should work] >You are right, he is wrong - the speed rating is related to the time the chip >needs for its output data to stabilise after the 'Read' signal is asserted >(for the purists - this is s Gross Simplification). Having chips >that are too fast just means they sit around with valid data for >longer - They should work perfectly. >-Howard. Not exactly correct. There is a possibility that the data may become valid too soon. I teach my students about microprocessor timing in my courses. One of the problems that can occur is data latency from a previous device access. Old data from some other device may be on the bus at the same time that the RAM data appears. This causes a bus conflict. This may manifest itself in the form of a parity error. (I used to consult for a company that repaired IBM desktops. Original IBM-PC/XTs used a combinational logic design to detect parity. Results were sent to the NMI*. Bus conflicts caused parity errors - sometimes.) With a reasonable design this problem is unlikely unless you go overboard (<80nS parts in a board designed for 120nS). These numbers are just examples. Without a complete timing analysis of the system (which, I suspect, not even some manufacturers are doing), there is no guarantee. - Dwight - -- Dwight W. Gordon, Ph.D. Kansas State University dwgordon@matt.ksu.ksu.edu Electrical and Computer Engineering dwgordon@ksuvm.bitnet Durland Hall Phone 913-532-5600; FAX 913-532-7810 Manhattan, KS 66506-5105
axa12@po.CWRU.Edu (Ashok Aiyar) (06/26/91)
Since you mentioned thta after you installed the new SIMMs, you geet absolutely not response from the computer (normally at least the initial diagnostics flash up), I wonder if there is any (ever so remote) possibility that you burned the SIMMs accidentally by static? I have installed 80ns SIMMs in a DELL (I don't remember the model, but it was a 25Mhz 386), and there was no problem. Just a thought, -- Ashok Aiyar axa12@po.cwru.edu aiyar@cwbio.bioc.cwru.edu