truel@iuvax.cs.indiana.edu (Bob Truel) (08/09/89)
In article <460@mit-amt.MEDIA.MIT.EDU> adam@mit-amt.MEDIA.MIT.EDU (Adam Glass) writes: >You're quite wrong. Mac II series computers will work just fine with 150ns >SIMM chips. For all normal use, there is no apparent slow down at all. In >fact, you can't tell the difference between the two except if you have a >SIMM tester or you happen to look at the chips. I don't know about these new dynamic memory, but it used to be that speed rating had nothing to do with how fast the chip did anything. That is, 150ns chips do not run slower than 120ns chips at all (as Adam suggested in a previous post) only hotter at the same speed. So 150ns chips should run at the same temperature at 150ns as 120ns chips run at 120ns. If you run them faster then they will use up more energy and burn out. I am not sure whether your mac is at any risk from RAM burning out (I doubt it) but it always seems a good idea to avoid potential disasters if you are doing anything besides game playing on your mac. Furthermore, this is the reason why 80ns chips will not speed up your mac. The faster chips are still being fed the same clock cycle and so are still running at ~120ns (although cooler). If I had one improvement for the macintosh II hardware, it would be to fix this. With the 680x0 family's asynchronous bus, it would be a simple matter to put the memory acknowledge hardware on the SIMMs themselves. A chip full of buffers wired in series would give a good delay. Of course this would mean nonstandard SIMMs I suppose, but banks of SIMMs could have jumpers on the motherboard for the same purpose. Wait States: Just say NO. -- Robert N. Truel "Life sucks, of course, but it didn't have to suck quite like this" -- RJSJR truel@silver.bacs.indiana.edu truelr@iubacs.BITNET
jtw@lcs.mit.edu (John Wroclawski) (08/10/89)
In article <24441@iuvax.cs.indiana.edu> truel@iuvax.cs.indiana.edu (Bob Truel) writes: In article <460@mit-amt.MEDIA.MIT.EDU> adam@mit-amt.MEDIA.MIT.EDU (Adam Glass) writes: >You're quite wrong. Mac II series computers will work just fine with 150ns >SIMM chips. For all normal use, there is no apparent slow down at... I don't know about these new dynamic memory, but it used to be that speed rating had nothing to do with how fast the chip did anything. Um, sorry to disagree, but. The speed rating (access time) of a memory chip is the guaranteed maximum time between when when you set the inputs (address, etc) and when the data appears on the output lines. (Actually, a chip will have different access times for the different inputs - row address strobe, column address strobe, and chip enable...) Chips with faster access times make the data available faster. However, as you point out, this doesn't speed up a Mac II, which cares only that the data be available in 120ns. The reason that a 150ns SIMM generally works in a Mac II is that the 150ns is a worst-case time, assured over the chip's entire permissible range of temperature, power supply voltage, etc. Under normal conditions an average "150ns" SIMM will produce the data much faster than that, and things will work fine. However, if the SIMM actually ever does take the full 150ns, you will lose. Since this will only happen some of the time, you will probably lose in a particularly confusing manner. -john jtw@lcs.mit.edu