Re: bit addressing Byte Addressability And Beyond

On Wed, 01 May 2024 14:33:16 -0400, Stefan Monnier wrote:

I agree that with 64 bit addresses and memory that is pennies per
megabyte the tradeoffs are different but that horse left the barn 50
years ago.  And I still don't think that bit operations are common
enough to be worth using bits in every non-bit address.

 
Historically, the advantages vs disadvantages have indeed been rather
against bit-addressing.  AFAICT when the DEC Alpha came out was the most
favorable time: the first time that the cost was low enough (they
already had byte-addressing without byte-granularity of accesses,
they had plenty of address bits to waste, and there wasn't too much
existing 64bit code to break) to make the idea palatable.
 
Practical benefits are fairly limited, but it would just be The Right
thing to do, making it "easy" to eliminate some arbitrary restrictions
in languages like C such as the inability to take the address of a
struct's bitsized field.  It would also have given an extra 3 bits to
play with for tagging purposes :-)

The TMS340[12]0 were bit-addressed 32 bit processors.

<https://en.wikipedia.org/wiki/TMS34010>

I never programmed one in C but the addressing worked well for doing
graphics operations.