John W Kennedy wrote: > On Feb 4, 2009, at 7:18 PM, JOE Conner wrote: >> You are using base ten numbers that are internally represented in >> base 16 hexadecimal. > > Base 2 binary, actually. Base 16 was historically used by IBM > mainframes, but they are migrating to base 2 nowadays. (They also > support base 10, which Intel is unfortunately stalling on.) > > Yes, there is a difference between base 16 and base 2. In 1964, IBM > thought there wasn't. They were wrong. > Many early computers, including some from IBM worked in decimal, using a modified hexadecimal system. One method that was used in an ancient computer I used to work on was called "excess 6", IIRC. This method used four flip flops to hold a number, but if you read the binary it was actually 6 more than the decimal value. This made it easier for the stage to overflow and pass on the carry bit to the next stage. Setting one stage to 6, representing 0, was easier than detecting a binary equivalent of 10 for the carry etc. IIRC, it was IBM's commercial line that used decimal, whereas the scientific stuff ran binary.
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