Meaning of "architecture width" - Re: 68K Macs with MacOS 7.5 still in production use...

On 09/15/2016 11:18 PM, ben wrote: Nope, that can't be. 1620 is a decimal machine (normally) and while the memory interface is 12 bits, two of those bits are parity bits, so you can't count those. That leads to "bytes" of 10 bits, two of which are flag/sign bits, so they don't really enter into computation. That is, the smallest unit on which one can do arithmetic is two decimal digits, with one flag bit serving as field demarcation and the other serving as sign. While you might call this a 10 bit machine, that's misleading. There are special bit patterns that mean things (such as 8-2 bit, which means a record mark, but the special combinations must be read, as there's no way to generate or test for them programatically. There are no visible registers; i.e., there's no way to query the P-counter directly. My point is that there are many machines that defy simple labels. Harvard architecture machines can be sioppery--take the humble PIC it its simplest form--12 bit instruction words that may also contain data, but 8 bit computation and data registers. I'm aware of supercomputers with 512 bit memory paths that, for example, can compute 128 bits per cycle, but have 64-bit GP registers. --Chuck