3 Oct
2024
3 Oct
'24
5:51 p.m.
The IBM 360 single precision floating point has a range of 10**-79 to 10**75; double
precision and extended precision has the same number of bits for the exponent.
From: "Paul Koning via cctalk" <cctalk(a)classiccmp.org>
To: "cctalk" <cctalk(a)classiccmp.org>
Cc: "David Wise" <d44617665(a)hotmail.com>om>, "CAREY SCHUG"
<sqrfolkdnc(a)comcast.net>et>, "Paul Koning" <paulkoning(a)comcast.net>
Sent: Thursday, October 3, 2024 10:39:47 AM
Subject: [cctalk] Re: Might be antique computer parts --1620
On Oct 3, 2024, at 12:01 PM, CAREY SCHUG via cctalk
<cctalk(a)classiccmp.org> wrote:
I worked on a model 1 with 40k memory (my very first computer experience) and floating
point, and later a model 2 stripped. I believe the model 2 still used table lookup for
multiply.
Sure enough, that's what the Model 2 manual I just found on Bitsavers says. I always
though that both add and multiply were in hardware. Interesting. Another major enhancement
in model 2 is index registers.
floating point in model 1 (and I think model 2) was
limited to a 98 digit mantissa, still more precision than the hardware in any subsequent
computer AFAIK. since the exponent was 10**-99 to 10**99 a broader range than any computer
till many years later I think.
100 digits says the model 2 manual.
Exponents larger than that do appear in machines of that era. The CDC 6000 series goes up
to 10**322 (11 bit signed binary exponent) and the Electrologica X8 to 10**644 (12 bit
signed binary exponent). Both are early 1960s. I don't remember what the IBM 360's
range is; the exponent field is fairly small but it's a power of 16 rather than the
usual power of 2 (or power of 10 as in the 1620).
...
don't know if the disk i/o RPQ overlapped, I saw one through a glass window once.
No, just like all the other I/O instructions they block the CPU.
paul