Path: utzoo!attcan!uunet!yale!husc6!cfa!ward From: ward@cfa.harvard.EDU (Steve Ward) Newsgroups: comp.arch Subject: Re: History of personal computing (LONG Summary: oops, the devil made me do it, DRAM's Message-ID: <1077@cfa.cfa.harvard.EDU> Date: 10 Aug 88 22:23:17 GMT References: <5946@venera.isi.edu> <46500024@uxe.cso.uiuc.edu> <1075@cfa.cfa.harvard.EDU> Organization: Harvard-Smithsonian Ctr. for Astrophysics Lines: 41 Well, DRAM's used to work that way 15 years ago! Seriously, for some reason (the devil made me do it) I was thinking of those old, very dynamic, CCD-style memory devices. The absence of a clock line on current DRAM's should make one suspicous as to its true nature. Present DRAM's utilize a static X-Y array of capacitors read via sense (comparator) amps. There is one capacitor for one bit. The capacitor charge is renewed during the read cycle. (isn't this a logical shift register of length 1? :-) ) The read cycle is clearly the place and time to do this since one has to know what to refresh. Back to the original topic, magnetic cores used a destructive readout method that inherently destroyed in absolute terms the stored information. This may be splitting hairs, but I don't think that this is the case with reading a capacitor charge via a comparator. Allright, maybe in practical terms the charge is emaciated to the point of unreliability without immediate refresh. Though I had the wrong device, my point was that the readout process wasn't inherently destructive in the way it is for magnetic cores. I still have my flame retardent undies on. :-) Here is one write-in response: -> Your understanding of DRAM operation is wrong, not even close. No, DRAMs never -> use shift registers for storage. You probably confused DRAMs with bubble -> memories or CCD RAMS. DRAMs are similar to SRAMs in that a 2D array of memory -> cells is addressed using x-y decoding. DRAMs store the data bits in capacitors -> instead of the latches used by SRAMs. Reading the capacitor state is -> destructive because most of the charge flows out to the sense line. Get your -> facts straight before you pose as an authority. I don't recall posing as anything, let alone an AUTHORITY. Does this mean most people just BELIEVE whatever I write? Hmm, posibilities...... :-) :-) Steven Ward ward@cfa