Craig Stuntz’s Weblog

In the beginning, Win32 apps had a 2 GB virtual address space. The /3GB boot.ini switch allows you to increase that, and, consequently, break any apps which presumed it could never be higher. After a good long while, many apps were updated to support /3GB. Delphi 2006’s memory manager can deal with it, for example, and you can give /3GB support to apps built in older versions of Delphi by using a third-party MM such as FastMM. Keep in mind, however, that it’s not just your own EXE which must be safe for /3GB but also any DLLs you might happen to load as DLLs will share your address space. Also, MM support is not by itself enough to make your app safe; you must also take care with any pointer arithmetic you may do in code. Now Win64 raises the VAS for 32-bit apps to 4 GB. As far as I know FastMM/D2006 apps should still be OK, but some other applications which could deal with /3GB in the past are failing under WoW.

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