From owner-freebsd-hackers Thu Jun 27 20:36:21 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id UAA02585 for hackers-outgoing; Thu, 27 Jun 1996 20:36:21 -0700 (PDT) Received: from MindBender.HeadCandy.com (root@[199.238.225.168]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id UAA02578 for ; Thu, 27 Jun 1996 20:36:15 -0700 (PDT) Received: from localhost.HeadCandy.com (michaelv@localhost.HeadCandy.com [127.0.0.1]) by MindBender.HeadCandy.com (8.7.5/8.7.3) with SMTP id UAA05788; Thu, 27 Jun 1996 20:35:38 -0700 (PDT) Message-Id: <199606280335.UAA05788@MindBender.HeadCandy.com> X-Authentication-Warning: MindBender.HeadCandy.com: Host michaelv@localhost.HeadCandy.com [127.0.0.1] didn't use HELO protocol To: Joe McGuckin cc: hackers@freebsd.org Subject: Re: What is EDO memory? In-reply-to: Your message of Thu, 27 Jun 96 19:40:03 -0700. <199606280240.TAA03861@ns.via.net> Date: Thu, 27 Jun 1996 20:35:37 -0700 From: "Michael L. VanLoon -- HeadCandy.com" Sender: owner-hackers@freebsd.org X-Loop: FreeBSD.org Precedence: bulk >What is EDO? Why doesn't it come in parity? >Is it faster than standard ram? This is my understanding of it... EDO (Extended Data Out) DRAM is capable of bursting faster than regular DRAM (Dynamic RAM). For example, it might take six clock cycles to get the first word, then four cycles for each additional word, once the intial address is setup by the memory logic. This is usually designated like: 6-4-4-4, indicating the bus cycles required for a burst of four words. This is why we have cache -- all those clock cycles are cycles where the CPU is twiddling its thumbs waiting for data. Cache runs faster than DRAM, so can retreive data without all those wait states if you get a cache hit. Most decent cache SRAM can do somewhere between 2-1-1-1 and 3-2-2-2. EDO RAM starts a transaction like regular DRAM, but after the initial address setup, is able to burst data through with less wait states, say two cycles instead of four for each following word: 6-2-2-2. EDO was originally touted as a way to make motherboards without cache. But, it's obvious the performance, in spite of being better than DRAM, just isn't as good as with a cache *and* EDO. Another kind of RAM just starting to catch on is SDRAM, or Synchronous DRAM. Supposedly it's supposed to be able to do like EDO, but at the full speed of the bus for bursts, so something like: 6-1-1-1. Although the setup time is still slower than cache, the following words are burst in quickly. SDRAM might actually be useful in low cost computers without cache. However, for the best performance, you'll still want cache in your machine (for faster setup times, and so the CPU can run from the cache while a DRAM refresh is in progress, or if a bus-master device is writing to memory while the CPU is doing something else). ----------------------------------------------------------------------------- Michael L. VanLoon michaelv@HeadCandy.com --< Free your mind and your machine -- NetBSD free un*x >-- NetBSD working ports: 386+PC, Mac 68k, Amiga, Atari 68k, HP300, Sun3, Sun4/4c/4m, DEC MIPS, DEC Alpha, PC532, VAX, MVME68k, arm32... NetBSD ports in progress: PICA, others... Roll your own Internet access -- Seattle People's Internet cooperative. If you're in the Seattle area, ask me how. -----------------------------------------------------------------------------