Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!elroy.jpl.nasa.gov!ncar!noao!arizona!dave From: dave@cs.arizona.edu (Dave P. Schaumann) Newsgroups: comp.sys.amiga.hardware Subject: Re: 32 bit memory??? Keywords: 32 bit memory is there really a difference???? Message-ID: <887@caslon.cs.arizona.edu> Date: 17 Feb 91 06:20:23 GMT References: Organization: U of Arizona CS Dept, Tucson Lines: 42 In article anderson@mrcnext.cso.uiuc.edu writes: >Friend says that there really isn't such a thing as "32-bit" memory. Dang. The jig is up. Hey, everybody, no more raking in big bucks on the "32-bit" scam. >[...] >but he says that the only difference is the size (ie: 1x8, 256x4...) >and the refresh speed (ie: 80ns, 100ns...). Ok. Here's a basic hardware lecture. You got your CPU, and you got your memory. They communicate through a "bus", which is really just some wires. The size of this bus determines how much data can be read and written to memory in one operation. On the 6502, the bus could transfer 8 bits at a time. That is why the 6502 is called an 8-bit CPU (even though addresses are 16 bits). Now, the 68000 is a 16-bit CPU (ie, 16-bit communication between the CPU and memory). This means, for example, if you want to load a long word from memory into the CPU, it takes 2 memory fetches, even though it is one machine op. Now this memory-CPU bus is sometimes called the Von Neuman (sp?) bottleneck, since memory response time is typically ~10 times slower than the CPU clock speed. This means that every time you want to read memory, the CPU has to wait for about 10 clock cycles. Perhaps now you begin to see the advantage of a 32-bit bus. A longword load will now go nearly twice as fast. A smart CPU will also be able to take advantage of this for byte and word accesses too, since memory is typically accessed in a sequential manner. I'm not familiar with the hardware architecture of the 680x0 family, so I can't really be more specific about Amiga hardware than that. But that's the jist of Why 32 Bit Memory Is A Good Thing. >Please help, I wouldn't mind if actually is right. Sorry. No such luck. -- Dave Schaumann | DANGER: Access holes may tear easily. Use of the access | holes for lifting or carrying may result in damage to the dave@cs.arizona.edu | carton and subsequent injury to the user.