on 8/31/05 4:27 PM, John Niven at [EMAIL PROTECTED] wrote: > On Aug 31, 2005, at 11:44 AM, Jeff Walther wrote: >> The pinout shows a separate data_in and data_out pin for each bit of >> the SIMM. In other words, it's an eight bit SIMM, but instead of >> simply having eight data pins Data[0:7] it has eight Data_In[0:7] and >> eight Data_Out[0:7] pins. > > The "by one bit" DRAMs had separate input and output pins. Most users > just tied them together and hooked them to a bi-directional bus. I > haven't looked into this, but I always assumed that what the IIfx did > was keep the In and Out busses separate so that the timing operations > could be overlapped thus speeding up memory operations. > >> That could imply that the IIfx SIMM requires bizarre dual data ported >> chips, but the chip examples I've identified (thanks Bob) seem to be >> normal DRAM chips. > > I assume the mother board has the "bizarre dual data ported chips" so > the SIMMs are unique in NOT hooking the In and Out pins together :-) > > > John > Didn't IIfx RAM's have nine bits for error detection? I seem to remember that there was something different about them and the RAM for a IIfx was unique to that Mac. All other Macs of that vintage had interchangeable RAM.
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