At 14:19 -0700 10/25/10, Andrew Liu Anderson wrote: > > Also, at 3GHz, you cross-over into the SHF range of micro-wave on radio > spectrum. As frequency increases, "Skin Effect" of AC current becomes more > dramatic, to where it becomes impossible to use ordinary conductors to carry > your clock pulses, data, etc. from one component to the next. You have to > start using "Wave Guides", or hollow tubes to transmit information along an > information pathway. And the wave guides have to be tuned to the frequency > you are using. The long and the short of it is that to keep going up in > frequency, we would need to start going back up in size to accommodate wave > guides, relays, etc. Soon we'd be seeing room-size computers again... Or at > least IBM 360 console size. :-) Anyone remember punch-cards? ***
It's the last question that makes me do this. I had an IBM 024 punch in my office that nobody else wanted because it didn't print the letters on the top edge. The 026's did. It's really fun to check a FORTRAN deck for typos when all you have to look at is the holes. But 3 GHz translates to a wavelength of 1/3 of a foot because the foot - a metric unit now that the meter is defined in terms of the speed of light - is the distance that light travels in a nanosecond. Those clocks you're talking about would be a full cycle out of phase in two inches round trip if you tried that on a memory bus. What the manufacturer really means is that you, the designer, give me something slower, a few MHz, on a pin and I'll multiply it up to a 3 GHz clock that stays wholly inside the microprocessor. There we're dealing with much shorter path lengths. The time delay in a wave guide is still limited by the speed of light. Bigger and longer doesn't get better. Homework: A 3000 mile cross country fiber is being driven at a rate of 3 Gb/sec. How many bits are in the pipe waiting to be read out? -- --> Halloween == Oct 31 == Dec 25 == Christmas <-- -- You received this message because you are a member of G-Group, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list
