APL\360

[Chuck Guzis]

On 1/29/21 11:40 AM, Nemo Nusquam via cctalk wrote:
> On 29/01/2021 14:20, Fred Cisin via cctalk wrote:
>> We don't need another BIG-endian/little-endian debate!
>> (when a 16 bit number is stored in bytes, does the high order byte
>> come first, or the low order byte?)  (cf. intel V Motorola)
> Amen to that (but did it not originate with DEC vs. IBM?)
> 
> N.

It was the result of sub-word addressable architecures.

Most old (pre S/360) digit/character-addressable architectures were
big-endian (i.e. higher-order characters occupied lower addresses)

Even PDP-11 isn't strictly little-endian, though Intel X86 definitely is.

Numbering of bits in a word is also interesting.  Is the high order bit
in a 64 bit word, bit 0 or bit 63?  Both conventions have been employed.

This really gets interesting on bit-addressable architectures.  STAR for
example, is bit addressable, but big-endian, with alignment of data
dependent on the data type (e.g. bytes must have the lower 3 bits of
their address as 000; halfwords as 00000 and so on.  However, it's
possible to extract any group of bits from a bit-addressed datum.

--Chuck


--Chuck