28 Jan
2008
28 Jan
'08
6:14 p.m.
Some people get rather upset at the lack of symmetry,
and lack of certain
instructions that might be handy, such as a load immediate into segment
registers.
There certainly are problems, not the least of which is the "shift 4
and add" segmentation rather than "shift N and add" where N is 11, 12,
14, or 16. Of course 16 is the right answer now, but in 1977 there
were logical reasons to want 11, 12, or 14. Never could come up with
a good reason to choose 4 except to artificially limit the expansion
address space to 1MB.
Lack of load immediate into segment isn't a big problem. Lack of "add
immediate to effective address" is a much bigger problem.