On 19/03/13 9:43 AM, Johnny Billquist wrote:
On 2013-03-19 14:30, Armistead, Jason wrote:
I had trouble with Timothe’s link to the USPTO, but found this same
patent in PDF form at
http://www.brouhaha.com/~eric/retrocomputing/dec/dectape/3387293.pdf
As a relative newbie who started my serious journey into computing with
an Apple ][ I’ve never fully understood DEC’s fascination with word
lengths that weren’t multiples of 2 ...
It wasn't just DEC. Back in the day, most everyone used various word
lengths that wasn't a power of two. I can't really make many comments on
why other word lengths were more popular.
12, 15, 18, 36, 60 ...
24 is still common in DSPs (and maybe 48 and 56?) - and even word
addressing is still used.
> I've seen mentioned that
floating point formats was pretty nice to do with something like 60 or
72 bits. Reason being that you had large enough exponents for useful
things, and enough precision for most calculations.
So a word length that related to this made sense.
Number of bits being a power of two started with IBM in the 60s, and
became common with the PDP-11 in the 70s. (Or so I'd like to think.)
And, not insignificantly, the rise of 8-bit microprocessors.
(Though octal was still standard notation for addresses and many
constants on PDP-11, hence C's octal literals.)
--Toby
Johnny
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