Microsoft KB Archive/89230

= Multi-User Access Not Supported in VB for MS-DOS ISAM =

PSS ID Number: 89230

Article Last Modified on 1/8/2003

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The information in this article applies to:


 * Microsoft Visual Basic for MS-DOS 1.0

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This article was previously published under Q89230



SUMMARY
Multi-user access is not supported in the ISAM engine of the Professional Edition of Microsoft Visual Basic for MS-DOS, version 1.0 (or in any other Microsoft Basic product). This means that you cannot design your ISAM database to be used by more than one user at a time. Multiple users may use the database program but no more than one user can have control of a file at any one time. (Multi-user ISAM support refers to the ability for multiple processes, or users on a network, to access different records within one ISAM file at the same time (with locking of individual records). The Professional Edition of Microsoft Visual Basic for MS-DOS and Microsoft Basic Professional Development System (PDS) versions 7.x do not support multi-user ISAM; these products only support single-user ISAM (where the whole ISAM file is locked during use by one program).



MORE INFORMATION
If a database is already open, the ISAM engine will generate a &quot;Permission denied&quot; error if another process attempts to open the database. If the first process closes the file, the second process can then access it.

The Professional Edition of Microsoft Visual Basic for MS-DOS was designed to ease the migration path from existing text-mode Basic to the new event driven model that Microsoft Visual Basic for Windows version 1.0 pioneered. Therefore, the Professional Edition of Microsoft Visual Basic for MS-DOS has to be as backwards-compatible with Microsoft Basic PDS versions 7.x as possible. Because one of the key features of Microsoft Basic PDS was high-speed, single-user ISAM, the same high-speed single user ISAM was included in the Professional Edition of Microsoft Visual Basic for MS-DOS. At the same time, the Professional Edition of Microsoft Visual Basic for MS-DOS has to be as compatible as possible with Microsoft Visual Basic for Windows, version 1.0. Where a feature in Microsoft Basic PDS does not exist in Microsoft Visual Basic for Windows, the feature was added to the Professional Edition of Microsoft Visual Basic for MS-DOS for compatibility with existing code. This was done because backward code compatibility is given high priority. No significant features were added to the Professional Edition of Visual Basic for MS-DOS that Microsoft does not intend to implement in Microsoft Visual Basic for Windows in a syntax-compatible way, for the same reason.

For multi-user ISAM access, you should use one of the third party database libraries or custom controls that are available for both Microsoft Visual Basic for MS-DOS and Microsoft Visual Basic for Windows.

Additional query words: VBmsdos 1.00

Keywords: KB89230

Technology: kbAudDeveloper kbVB100DOS kbVBSearch kbZNotKeyword3

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