DOS interrupt (read only) with NT

Hmm...interesting....looks like I need to look up more information
on registers....maybe that will help. Unfortunately, in school,
I never learned x86 Assembly....I learned MIPS

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Amos
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[Tom Hanlin]

AX is a 16-bit register, which can be addressed as two 8-bit registers,
AH and AL. Setting AX = &H3600 is the same as setting AH = &H36 and AL = 0.

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Tom Hanlin
PowerBASIC Staff

Well, in Ralph Brown's interrupt list, the sub function is
AH=36h, and it seems to work fine with how you stuffed 3600h into
AX....so I'm guessing, there is some kind of coincidence here...

Hope I'm right.

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Amos
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[Lance Edmonds]

Would that be casting to unsigned?

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Lance
PowerBASIC Support
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Ok, nevermind, I just looked at Lance's example, and figured out
what I am messing up....

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Amos
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[This message has been edited by Amos Vryhof (edited December 16, 2001).]

While we're on this topic, Is there any way to access AH
from PowerBASIC?

I am playing around with some of the stuff on Ralf Brown's
interrupt list, using REG, and CALL INTERRUPT, but I want
to go further.



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Amos
mailto:[email protected][email protected]</A>

[Mark Hunter]

michael mattias wrote in http://www.powerbasic.com/support/pb...read.php?t=516

"you cannot access the winapi from a dos program,
but you can access the winapi from a windows program
which is shelled from your pb/dos program."

so the program could get the free disk space by shelling
to a pbcc executable that writes the number to a file,
and then reading the file.

but it's a bit complicated if it's to work for all
versions of windows. from the pbcc help-file for
pbcc's function diskfree (slightly paraphrased):

"in 32-bit windows, a maximum of two gigabytes is
returned, even if more free space is available. in
some early versions of windows 95, diskfree may
return a negative value for drives or partitions
larger than two gigabytes.

"the getdiskfreespaceex api retrieves the free space
on a disk. however this api is not available in
early versions of windows 95 (pre-osr2). it is
available on all versions of windows that support
fat32 or ntfs file systems."

[Lance Edmonds]

No, definitely not at all in my experience.

For example, the following code reports around 970Mb free on most of drives under Win2K (aka, NT5) when there is, for example, 3.86Gb free.

Ditto for network drives, and can give VERY unusual results for CDROM drives if the DOS CDROM drivers are not enabled in CONFIG.NT and AUTOEXEC.NT. On my systen here, it reports the CDROM drive as having 484Gb free when there is no disc in the drive!

function FreeSpace&&(Drive%) local public
        reg 4, Drive%
        reg 1, &H3600
        call interrupt &H21
        function = cqud(bits??(reg(2)) * bits??(reg(3)) * bits??(reg(1)))
end function

I filled one one NTFS drive so that there was 1.76Gb free and it still reported 970Mb.

The moral: don't read all you believe from that interrupt.

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Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Mark Hunter]

"Reading the result with drives > 2 Gb is unreliable."

One limitation is that since DOS gives the answer
as a double word, the largest number of gigabytes
it can measure is

2^32 / 1024^3 = 4

So if you have more than 4 gigabytes free, it
can't measure it (maybe it wraps through 0).

Otherwise is it reliable with 95/98 and
with NT/2000/XP ?

[This message has been edited by Mark Hunter (edited December 15, 2001).]

[Peter Lameijn]

Theoretically: It still works.
Practically : No support for modern large drives. Reading the result with
drives > 2 Gb is unreliable....
(Using the Win API functions is really the best solution)

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Peter.
mailto[email protected][email protected]</A>

[Mark Hunter]

I don't have Windows NT. Will the following
work in a PBDOS program running under NT without
the user having "special priveleges"?

'' DISKFREE
! mov  AX,&H3600      ; function 36h, get drive info
! mov  DX,DriveNum    ; requested drive
! int  &H21           ; call DOS