I need to perform the equivalent of an INT 25H (Absolute Sector Read) and
INT 26H (Absolute Sector Write).
How can I do this in VB6?

Thanks,

AFAIK to do this you need to 'Thunk' - that is, move into 16bit mode.

I shall watch this thread with interest.

This looked promising:
http://www.planet-source-code.com/xq/ASP/txtCodeId.21381/lngWId.1/qx/...
pts/ShowCode.htm
But using the file name \\.\A: did not yield the reading of the sectors of
drive A:.  Also when trying to
position the file pointer and reading it always yielded the beginning of the
file.

<snip>

For my project I am creating a disk server which feeds requests from a
serial port.

<snip>
Disk Devices
Windows NT: You can use the CreateFile function to open a disk drive
or a partition on a disk drive. The function returns a handle to the
disk device; that handle can be used with the DeviceIOControl
function. The following requirements must be met in order for such a
call to succeed:

     The caller must have administrative privileges for the
operation to succeed on a hard disk drive.
     The lpFileName string should be of the form \\.\PHYSICALDRIVEx
to open the hard disk x. Hard disk numbers start at zero. For example:

String  Meaning
\\.\PHYSICALDRIVE2      Obtains a handle to the third physical drive
on the user's computer.

     The lpFileName string should be \\.\x: to open a floppy drive
x or a partition x on a hard disk. For example:

String  Meaning
\\.\A:  Obtains a handle to drive A on the user's computer.
\\.\C:  Obtains a handle to drive C on the user's computer.

Windows 95: This technique does not work for opening a logical drive.
In Windows 95, specifying a string in this form causes CreateFile to
return an error.

</snip>

Basically the stuff at PlanetSource shows you how to use the
CreateFile API - under Windows NT CreateFile allows you to 'open' a
floppy directly - by{*filter*}ering around with the file name.

All profoundly useful if you are not using Win NT - and IMO a damn
stupid way of doing things - imagine a slightly smart user entering
\\.\C: as a file name.   The thought is horrific.

As yet I am not familiar with 'thunking' - and I must confess that I
only use Int 25 and (more seriously) Int 26 under some duress, but I
would recommend that you get hold of a copy of 16 bit Delphi and use
that to write the stuff you need.  

You should be able to drive it via SendMessage.

Why do you need Absolute Disk write for something that is servicing a
COM port ? - or am I missing something ?

Howard Henry Schlunder

I've written a fairly semi-complete volume imaging program which does very similarly what you are talking about.  I never thought I would release it in any fashion, but oh well.  Full source and a signed executable can be downloaded from [ http://venus.ajusd.org/~hschlund/products/VolumeImager.zip ].  I usually use it to copy floppies and CDs to my hard drive.

The main thing you have to keep in mind when working with volumes like this is that you have to read and write a whole sector at a time.  I believe the same goes for seeking.

Howard Henry Schlunder

John Newbigin wrote rawwrite for windows which can be found here:
http://uranus.it.swin.edu.au/~jn/linux/rawwrite.htm
On that page is a link telling how to access a disk:
http://uranus.it.swin.edu.au/~jn/linux/diskio/index.htm

He has already written and thunked a dll called diskio.dll that should do
the trick.
However, I am not quite clear in how I was call it from my VB6 program.

In the DLL is several functions and one being that to set which disk you are
using.
First off I am just trying to call the function SetDisk.  In my VB6 program
I put in:
Private Declare Function SETDISK Lib "DISKIO.DLL" (disk As Integer) As
Boolean

In my code I have a call to SetDisk(0).  However, I get RunTime Error 48
File not
found diskio.dll.  I have the dll in the same directory and even copied it
to the windows
system directory.  Can someone tell me how I can use this dll from VB6?

Thanks,

From searching the web it looks like I will need to thunk to these
routines.  Can anyone tell me how I to do this in VB6?

Thanks,

ChDir App.Path  in the{*filter*}statement will fix it

It is simply that for some idiotic reason, in the IDE the default
directory is not the App.Path - so the DLL is not found.

I am off for a week in literally a few minutes - if you have not
solved the problem then Email me.

I've found a DLL called "DIRECT32" which does parts of what I need.

Private Declare Function pb_Unload16 Lib "DIRECT32.DLL" (ByVal hDLL As Long)
As Long
Private Declare Function pb_Load16 Lib "DIRECT32.DLL" (ByVal dllName As
String) As Long
Private Declare Function pb_GetProc16 Lib "DIRECT32.DLL" (ByVal zDll As
Long, ByVal zFunction As String) As Long

Private Declare Function READDISKGEOMETRY Lib "DIRECT32.DLL" Alias
"pb_Call16" (ByVal hProc As Long, Param1, Param2) As Long

Dim hDLL As Long
Dim pfnDTest As Long
dim a

    hDLL = pb_Load16("DISKIO.DLL")
    pfnDTest = pb_GetProc16(hDLL, "READDISKGEOMETRY")
    a = READDISKGEOMETRY(pfnDTest, Param1, Param2)
    pb_Unload16 hDLL

The loading of the 16bit dll works and the call to GetProc16 works.
I am not sure how to declare READDISKGEOMETRY.
I believe the first parameter is a pointer to sector info which is
byte word byte byte byte
The second parameter should be the size of the structure, but not sure
if it is a interger or long.

Thanks,