Hi :-)

> - Sorry, somewhat new terms to me, need to study a bit... INVLPG seems
>  to be assembler command..? Anyway this machine is pentium, about 10years
>  old. I have GRUB dualboot FreeDOS/Slitaz 4.0 Not fast but everything
>  works (except Autocad issues..)

Older Pentium may have limited performance in the "virtual"
mode which all EMM386 style drivers use, but maybe you find
some tuning options in the documentation of JEMMEX/JEMM386.

As already mentioned, you can also try non-virtual EMS for
special cases, but that or for example UMBPCI has hardware
requirements which are less flexible than for EMM386 style.

>    Autocad manual states that EMS is supported. It is recommended
>  as CAD programs are memory hungry...

If Autocad supports XMS as well, I would prefer that instead
of EMS. Note that most EMM drivers also provide UMB, which
let you load drivers outside the 640k of classic DOS memory.

But if you only need more free space in the 640k, UMBPCI can
be a good alternative. Also, FreeDOS drivers often use less
DOS memory than old drivers from MS DOS time anyway :-)

To get XMS, load XMGR, FreeDOS HIMEM or similar drivers. To
get UMB, load any EMM driver or UMBPCI. Note that for HIMEM
you can sometimes select "gate A20 methods" for tuning, but
autodetection is usually fine. Of course you have to select
a method which actually works. If not, you get crashes when
HMA or XMS are first used, e.g. DOS=HIGH activates, FreeCOM
command.com loads or disk cache or ramdisk drivers start up.
If that happens, reboot and skip the XMS driver with F5/F8,
then edit the options to select another A20 method.

> - Thank you mentioning EMSMAGIC, I found information about it,
>  seems to be promising.

Keep us informed :-)

> - AutoCAD products were MSDOS programs of that era those days, (also
>  UNIX versions available), I used this version on DOS 6.?? at that time.
>  Requirements 286 and  up. This version (AutoCAD R9, v2.7,
>  september -87) was the firs to  need arithmetic unit mandatory.

Interesting. Before 486dx, floating point units were expensive
extras, so I would have assumed that AutoCAD also requires 386
or newer CPU. Because those also have 32 bit integer arithmetic
built in, which is good even if you also have floating point.

> - Native FreeDOS yes, I choose it on start (by GRUB)
> - System information shows: Intel board D845GERG2
>  Intel BIOS RG84510A.86A.0031.P16.0304111002
>   Intel Pentium 4, 2.4GHz

Pentium 4 is much more modern than Pentium, there should be
no performance problem with EMM386 or JEMM style drivers...

Maybe your BIOS is configured to support "legacy USB" methods
to let DOS access USB keyboard or mouse without USB drivers?
In that case, the BIOS can spend quite a lot of time to deal
with the USB controller. Try using USB keyboard and mouse. To
be on the safe side, leave the legacy USB support on anyway,
it will not waste much time if no devices are active and you
may need it to navigate the BIOS CMOS setup config dialog :-)

> - I tried to "open" ACAD.EXE by Leafpad editor to see some cleartext.
>  The file started <MZ...> so obviously MZ...?, as expected?

Yes. It may also have some messages about Windows a bit later
in the file - then it could also support running directly as
Windows program.

> - No DOS extender, just JEMMEX, to me to know. I am not sure if
>  I understand the difference.

AutoCAD will probably use some library to make efficient use
of extra memory. However, if it is really 286 compatible, it
will not be a very heavy user of modern CPU features. A DOS
extender normally lets DOS programs run as "protected mode"
tasks and helps them to communicate with DOS itself, which
runs in real or "virtual" but not in "protected" mode. This
of course has an overhead which can cause interrupt delays.

The advantage is that protected mode tasks can directly use
many megabytes of RAM without having to request access each
time. With EMS, the access is managed by making small pieces
of RAM visible in the first megabyte of (DOS) RAM, while in
the XMS case, the XMS driver copies blocks of data around on
request. In both cases, without a DOS extender or other ways
to use protected mode, the program itself (e.g. AutoCAD) is
running in the first one megabyte of memory...

> * > For now I am searching a solution to strange speed dependency of serial
> * port
> * > data flow. Responce to many commands are extremely slow unless I
> * > "refresh" the computer by RS232 output (input to computer) by rubbing
> * > the surfce of tablet with digitizer pen. Program acceleration is
> * > readily seen according to swipe velocity of pen. When sweeping the
> * > tablet surface it sends position data to serial port maybe max. some
> * > hundreds of points per second. Beyond certain speed the program does
> * > not accelerate any further, that may be limited by tablet. (Kurta
> * > IS/ONE).

For that, you can probably check documentation of AutoCAD,
tablet and drivers - maybe acceleration and sensitivity can
be configured and maybe your "too fast" Pentium 4 causes a
non-smooth interaction experience with the default settings.

Note that it may make a difference in which sequence your
drivers are loaded as well, for example EMM versus PENSMITH.

> - FYI, when I need openGEM I usually load mouse driver which seems to
>  replace digitizer driver and mouse begin to work. Then, when entering
>  Autocad its batch file loads digitizer driver again without causing
>  conflict. Maybe this tells something... to somebody...?

Order of drivers can make a difference. You have not said
which type of mouse you have, though (PS/2, RS232, USB...)
but your tablet seems to be RS232. Depending on which are
on which COM port, they might interact in interrupt usage.

> * >  In general it seems that those commands suffering of slow speed
> * > are mostly those related to display calculations (REGEN.. floating point,
> * >  badly  and REDRAW... integer, slightly) and also printing (print vector
> * > calculation, Autocad displays it progress, easy to observe)

The Pentium 4 with built-in floating point and probably a
PCI, AGP or PCIe graphics card should be easily fast enough.

Of course CAD always means heavy computations and your DOS
AutoCAD can only use one CPU core. Versions for Linux or for
Windows can use multiple cores and multiple CPU if present.

Also, AutoCAD for DOS cannot switch your graphics card bus
speed to the maximum possible in AGP or PCIe, but there are
tools for DOS which can help you with that. Maybe by RayeR?

>  ... since 486DX I didn,t need FPU any more. Display REGENeration
>  is one of most "CPU demanding" task so it is just obvious to show
>  speed limitation first there.

See above - since 486DX, FPU is always included in the CPU.

Regards, Eric

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