How to Specify the Base Address of a VB OLE Server DLL

• Professional and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SUMMARY

It is possible to specify the preferred address in memory where you want an OLE DLL that was created in Visual Basic to be loaded. If the OLE DLL is unable to load at the preferred address, it automatically finds a suitable address; however, the OLE DLL may take longer to load into memory in this case, and will consume more system resources (swap file and possibly memory). By specifying a base address, you may improve the performance of the OLE DLL by anticipating and avoiding conflicts with other OLE DLLs.

MORE INFORMATION

With Win32, each process has its own 4 GB virtual address space. Any DLLs that the process might use, are loaded into this address space. If a DLL could be loaded as is using the addresses within it as calculated from the specified base address, then it can be memory mapped right off the disk. No relocation is required. However, if relocation is required because some other DLL is occupying the memory at the specified base address or because of another use of that memory (such as memory-mapped files, memory allocations, reserved virtual address ranges, and so on), then a new temporary copy of it is automatically made with the new offsets and mapped onto the new memory location in the process's virtual address space.

Memory addresses beyond the location 11000000 are typically used by Visual Basic OLE DLLs. So this is the default value of the base address that is used if you don't specify one when compiling the DLL.

If your application uses two DLLs, you can load them faster by specifying appropriate base addresses. You could specify the default base address for the first DLL and add the size of this DLL to this base address in order to determine the base address for the second DLL.