Subject: Re: [stella] What's magic about a byte? From: Chris Wilkson <ecwilkso@xxxxxxx> Date: Thu, 14 Apr 2005 01:17:58 -0400 |
Heh. Yeah, I'm a hardware geek. :) Here's another one...a little (not much) less technical, and maybe an urban legend, but perhaps a bit more interesting from the human-technology interface perspective... Are Religion/Mythology responsible for "modern" word sizes? The story: So MIT was supposed to provide the onboard computers for NASA's Gemini program. But some authority figure in NASA balked because the plan was for a 13-bit data word. "Too unlucky!" Back to the drawing board. The irony is that the final Gemini computers, from IBM, used a 13-bit instruction and a 26-bit data word. Heh. A trilogy of 13's!!! Rumor has it that the original MIT design was scaled back to 12-bits to make the superstitious people happy, but it took too long. The design eventually became the PDP-8 minicomputer. Having learned from its mistakes, MIT designed the machine used in Apollo to have a 16-bit word instead. Whee! -Chris On Thu, 14 Apr 2005, Ruffin Bailey wrote: > On Apr 13, 2005, at 11:57 PM, Chris Wilkson wrote: > > > On Wed, 13 Apr 2005, Ruffin Bailey wrote: > > > >> Why would the number of bits in a byte have to have anything to do > >> with > >> powers of 2? The max number, whether 7 bit, 13 bit, or 8 bit would > >> still be a binary number. ?? > > > > Because decoders and encoders using bits as control lines will always > > address 2^n locations. Either you implement them, or you don't. But > > if you need 5 states, you need 3 bits to represent that. Then you have > > created 3 bogus states. You need to define them or else "Bad Things" > > can happen. You can define them by hardwiring, but you might as well > > make them useful if you can. > > > > In the case of decimals digits, you need 4 bits to encode each > > character > > with. If your system is already 6 bits, just to encode the text > > characters, > > you're wasting 2 bits when doing BCD. You might as well make your word > > 8 bits wide so you can encode 2 digits without waste. > > ... thus earning the mit.edu behind his email nick. ;^) > > Ruffin Bailey > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ > Unsub & more at http://stella.biglist.com > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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