5 Jul
2016
5 Jul
'16
7:22 a.m.
On Jul 2, 2016, at 1:37 PM, Fred Cisin <cisin at xenosoft.com> wrote:
On Sat, 2 Jul 2016, Eric Christopherson wrote:
Fred, I tried for years to understand the difference between .COM and .EXE. One post of
yours, and it?s clear. Thank you!
Genius.
Clever? yes. Genius? no, or you
would have to count too many of us.
But I would have thought CP/M would at least
require a .com file to
have a header.
http://peetm.com/blog/?p=55
NO.
A .COM file is a pure image of memory, starting at location 100h.
The "header" or "zero page" or "program segment prefix" is
generated on the fly during the loading of the program.
(There is a lot more to know about it) The first thing that I did in CP/M was to create a
zero length program. it seemed intuitively obvious as a needed capability.
Didn't everybody realize that and do it?
It never occurred to me to try to SELL it! In those days, there was almost an assumption
that price would be proportional to program length.
I would urge caution in this regard. Depending on the distribution of the dots on the
price/length plot, it?s not inconceivable that a least-squares fit would result in you
having to PAY people to accept your program, depending on where the line crosses the
?price? axis ?.
For those who wanted "source code" for it:
SAVE 0 A:JMP100.COM
(SAVE was one of the five CP/M internal commands, ERA,REN,DIR,TYPE)
?. uh oh. Too late.
:-)
- Mark