On 2022-06-17 19:02, Seymour J Metz wrote:
I'm not aware of any serial 1s' complement or 2's complement machines.
In this forum, just a few letters ago, I stated that Pilot ACE,
DEUCE, and ACE were serial machines that held negative values in
twos complement form.
You've made claims;
They weren't "claims". They are statements of facts.
that doesn't mean that they are true. There is
nothing that precludes any representation in an array machine.
Don't talk nonsense.
These are statements of facts from my knowledge of how
those serial machines worked.
You are
begging the questions by the assumptions that you are making.
I made no assumptions.
On the other hand, your assertions are nonsense.
________________________________________
From: IBM Mainframe Assembler List [[email protected]]
on behalf of Robin Vowels [[email protected]]
Sent: Friday, June 17, 2022 4:54 AM
To: [email protected]
On 2022-06-17 18:04, Seymour J Metz wrote:
FSVO serial. The early electronic machines that I'm aware of were
parallel.
FWIW, there were papers claiming that 1s' complement was simpler.
Not in a serial machine.
What's more, I've already pointed out that in an array machine,
ones complement was impossible because you only got one look
at the operands and the result. The result had to be stored
in the same cycle as the operands were available, because the
next cycle the sum or difference of the next operands was required
to be performed. In a serial machine, the sum of a pair of
corresponding bits produces at the same moment the sum bit.
I
believe that the tradeoffs vary depending on the technology used.
________________________________________
From: IBM Mainframe Assembler List [[email protected]]
on behalf of Robin Vowels [[email protected]]
Sent: Friday, June 17, 2022 2:40 AM
To: [email protected]
Subject: Re: When did logical instructions appear?
----- Original Message -----
From: "Paul Gilmartin"
<[email protected]>
To: <[email protected]>
Sent: Friday, June 17, 2022 7:20 AM
On Jun 16, 2022, at 10:43:36, Robin Vowels wrote:
Computers have had instructions for signed and unsigned binary
since at least 1951. When negative values are expressed using
twos complement notation, ordinary addition will give the same
result whether the operation is signed or unsigned.
It puzzles me that some of the oldest computers employed sign-
magnitude notation when 2's (1's, 10's) complement would have
needed fewer gates and fewer clock cycles.
For a serial machine (and most of them were in the early days),
twos complement was the simplest. It needed only one cycle
for add and subtract. Even subtract (complement and add one)
was done in a single cycle, "on the fly". It was unnecessary to
add the one; complement commencing after the first non-zero bit.
Ones complement was a PITA, because a carry out of the high end
required a 1 to be added in the next cycle. This was no good at
all for array machines such as Pilot ACE, DEUCE, and ACE,
because the word just summed would not have been around
to add the final "1" produced by the carry out -- the arithmetic
unit already working on summing (or subtracting) the next pair
of words.
Perhaps an accommodation to the engineers' habits.
