INF: How to Calculate the Virtual Device Number

• Microsoft SQL Server versions 4.2x for OS/2

The following article describes how the virtual device number is calculated and where this information is stored.

Upon execution of the stored procedure SP_HELPDEVICE, one of the fields returned is a virtual device number (V_DEVNO). This number is the virtual device number that was entered when the disk device was created (using DISK INIT).

However, if you examine all of the system tables, there appears to be no table that holds a virtual device number. The number is stored in the LOW column in the SYSDEVICES table in the MASTER database.

Version 4.2 uses the following formula:

    device_number = convert (tinyint,substring(convert
                     (binary(4),sysdevices.low),spt_values.low,1))

 where spt_values.type = 3
       spt_values.number = 3
       sysdevices.name = "<specific device name>"