Byte sizes (was Re: 2.8M 3.5' floppy (was: three and a quarter loppy?)

[Scott Stevens]

On Mon, 14 Mar 2005 11:52:06 -0800 (PST)
"Eric Smith" <eric at brouhaha.com> wrote:

> der Mouse replied to my description of PDP-10 byte addressing (0-36
> bits) and someone else's claim that a byte is the smallest addressable
> unit of storage:
> > That sounds a whole lot like a hardware-supported way of addressing
> > an object of an arbitrary size in bits.  And that would mean that
> > bytes of any size *are* individually addressible.
> 
> Any size from 0 to 36 bits.
> 
> The problem with the "smallest addressable unit" definitition is that
> it would mean that the byte size of a PDP-10 is *only* zero bits,
> because that's the smallest.  (Or one bit, if you can define it in a
> way to rule out the zero bits case.)
> 
> Also, the MC68000 has bit-manipulation instructions that can address
> individual bits, but it is not considered to have one-bit bytes.
> 

Lots of embedded controllers, including some of the 4-bit ones that I've
programmed professionally (8 bit byte ??!!??) have bit manipulation
instructions. 
This is one of those discussion threads where the stuff people bring up
is more interesting than the actual issue of 'the size of the byte.'

> Eric
>