On 3/19/2013 7:27 PM, Toby Thain wrote:
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.
24-bit data is common for cost sensitive audio applications because
16-bit data is insufficient and 32-bit data is overkill.
GPUs typically have odd data widths for similar reasons.
In these types of applications, the notion of 8-bit bytes is mostly
irrelevant. As stated above, many of these devices can't even address
bytes. Interestingly enough, none of these /limitations/ preclude having
a compliant "C" compiler.
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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