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[ THE KAY*FOG RBBS | Filename=CPM-CC22.ART | posted 07/05/86 | 171 lines 10k ]
The CP/M Connection Originally published in
by Computer Currents
Ted Silveira 5720 Hollis Street
(copyright and all rights reserved) Emeryville, CA 94608
March 11, 1986
EMULATING CP/M
Several times in the last few months, I've mentioned CP/M emulators
that allow you to run CP/M programs on an IBM PC or clone. I've now had
a chance to play with one of these emulators, a package called
Acceler8/16 from Intersecting Concepts.
[What a CP/M Emulator Does]
A CP/M emulator is a program that makes an MS-DOS computer imitate
a CP/M computer, by creating CP/M environment within the memory space of
the MS-DOS computer. When a CP/M program runs, it sees nothing amiss
and chugs merrily away. In the background, meanwhile, the emulator is
running madly about, intercepting the CP/M program's instructions to its
fictional CP/M computer and translating them into instructions the real
MS-DOS computer can handle. Software emulators are usually cheap but
slow.
Recently, however, software emulators have gotten a hardware boost
from the NEC V20 chip, a pin-for-pin replacement for the 8088 chip
that's the brain of most MS-DOS computers. The NEC V20 not only runs
the same instructions that the 8088 does (and 10-20% more efficiently to
boot) but also can run the instructions used by the older 8080 chip.
And the 8080 just happens to be the chip for which CP/M was written
(though almost all CP/M computers now use the Z80 chip with its extended
instruction set, which causes some problems I'll mention later). When
the NEC V20 chip is flipped into its "8080 mode," it can execute 8080
instructions directly, so the emulator software doesn't have to do
nearly as much work. As a result, a CP/M emulator that takes advantage
of this chip runs about 300% faster than a software-only emulator.
[Acceler8/16]
Intersecting Concept's Acceler8/16 package was one of the first of
these software/hardware emulators, though there are now several others.
The full package consists of Media Master (a disk conversion program),
Accel (the emulator), and an NEC V20 chip to install in your MS-DOS
computer.
[Media Master] Media Master temporarily converts one or more of an
MS-DOS computer's drives so that it can read a "foreign" disk, such as
one from a Kaypro or Osborne CP/M computer. It can read and write a
large number of formats, both single and double-sided, including all the
common formats--Morrow, Kaypro, Osborne, Heath/Zenith, Televideo, Xerox,
etc.--and some I've never heard of--Beehive Topper, Idea Bitelex, and
Royal Alphatronic. It won't do Osborne or Xerox single-density, only
double-density.
Unlike some disk conversion programs, which convert a drive to a
foreign format and then leave it converted while you run other programs,
Media Master converts your drive only as long as Media Master itself is
running. From the Media Master menu, you can get directories of any
drive, erase files from any drive, type or print files, and of course
copy files from one drive to another, all with one or more of your
drives converted to a foreign format. But as soon as you exit Media
Master, you're returned to your native format on all drives. That means
you can't run the CP/M emulator, stick in a Kaypro disk, and run a CP/M
program--you have to copy the program to an MS-DOS format disk.
I tried out Media Master on several disk formats, and it handled
them all, with one exception. I found that while Media Master handled
single-sided Morrow CP/M disks without problems, on double-sided Morrow
disks (formatted on my Morrow MD3), it sometimes reported the disk space
used incorrectly (though the files and file sizes were correct). I also
found that my Morrow MD3 refused to read disks formatted by Media Master
in the Morrow format.
I talked to Mark Graybill at Intersecting Concepts about this
problem, and he quickly traced it to a bug in the Morrow MD3 format
table, a bug that apparently exists only in the particular version I
have (3.0) and not in earlier or later versions. The company's policy
is to fix such bugs free (applause), so a new disk is on its way. Any
of you who also have this problem should contact Intersecting Concepts.
[Accel] Accel, the actual CP/M emulator program, comes in four
versions. The first is a plain vanilla version. The other three
emulate the video characteristics of a Kaypro, an Osborne, and a
Heath/Zenith H19 terminal, respectively. This terminal emulation works
well and lets you run CP/M programs without reinstalling them, if they
originally were installed for the Kaypro, Osborne, or H19.
When you run Accel, it creates a CP/M environment complete with the
built-in commands like DIR and ERA. It also includes a few ZCPR-like
enhancements such as automatic search of drive A for programs. The only
noticeable difference from normal CP/M is that all your CP/M programs
must be renamed using the filetype CPM instead of the usual COM (so MS-
DOS won't confuse them with its own COM files).
You can run Accel by itself, without the help of the V20 chip, but
like all software-only emulators, it's so slow that it will drive you
crazy. If you have the V20 chip installed, however, the performance
isn't bad. While there's some argument about whether benchmark
performance is slightly better or slightly worse than a typical Z80
computer, what I noticed most was the screen speed (the speed with which
the computer can fill up the screen with text or whatever). The screen
speed using the Kaypro terminal emulation is slower than that of my CP/M
Kaypro. And the Kaypro itself is not a speed demon, being slower than
my Morrow (with a Televideo 925 terminal running at 19,200 bits per
second). I found the results good enough to be usable, but I did get
tired of waiting for things to happen on the screen.
Accel runs pretty much everything it claims to, which means
everything that's written for generic CP/M and uses only the 8080 chip
instruction set, but it does have a few limitations. As I mentioned
earlier, most CP/M computers now use the Z80 chip, which has some extra
instructions that the 8080 doesn't. Programs that use these Z80-only
instructions won't run under Accel, but fortunately, most CP/M programs
stick to the 8080 instructions (so they can run on as many CP/M
computers as possible). Accel also won't run programs that use certain
BDOS and BIOS calls, mostly ones that work intimately with the disk
drive (BDOS functions 27 and 31, and BIOS functions 8 through 16).
Programs that will run include DDT, ASM, dBase II, and the new
OutThink thought processor from Kamasoft. Programs that won't run
include SD, NSWP207, UNERASE, and DU (or any other disk editor).
WordStar will also run under Accel, but if you have the Kaypro
factory-installed CP/M WordStar, be prepared for some problems, since
Kaypro modifies the program. So far I haven't been able to get this
version to run. When I first tried running the Kaypro WordStar, the
computer would load it and then immediately reboot, returning me to the
A> prompt without doing anything. I then remembered that Kaypro
modifies its versions of WordStar to program the cursor keys, so I dug
into it with DDT and disabled the offending code (at locations INISUB,
UNISUB, and MORPAT).
When I tried this new version of WordStar, it loaded and went to
its first menu just as it should, but then it refused to do anything
except exit. It acted as if it couldn't find its two overlay files,
WSOVLY1.OVR and WSMSGS.OVR, even though I verified that they were on the
disk. I haven't yet figured out what this second problem is--more
information next time (I hope).
Overall, both Media Master and Accel do what they claim to. Except
for the quirk with Morrows, Media Master seems a solid program, and
while Accel (when combined with the NEC V20 chip) won't blind you with
its speed, it is usable . . . and miles ahead of any software-only
emulator. I do wish it were possible to use "foreign" disks directly
while in the CP/M mode, but I can work around that. (I've heard that a
similar program, RUNCPM from Micro Interfaces, does allow this, but I
haven't seen it.)
If you're interested in CP/M emulators--and you must be if you've
hung around this long--you might also want to look for a copy of the
February 1986 Computer Shopper, which has an article comparing half a
dozen emulators.
Acceler8/16
$99.95
Intersecting Concepts, Inc.
4573 Heatherglen Ct.
Moorpark, CA 93021
805/529-5073
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Ted Silveira is a freelance writer and contributing editor to several
computer-oriented publications. He appreciates suggestions or feedback
and can be reached through the KAY*FOG RBBS (415)285-2687 and CompuServe
(72135,1447) or by mail to 2756 Mattison Lane, Santa Cruz, CA 95065.
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