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

Eric Smith eric at
Mon Mar 14 13:52:06 CST 2005

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.


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