It stores the necessary info to restore executables (*.exe, *.com) files.
Actually, VRDB scans all the local hard disks for executable files and stores some info about them. So, it doesn’t care if the files belong to Win98, Win2000, or to a third-party application (as long as it is able to access the files - i.e. NTFS partitions certainly won’t be scanned from Win98 OS).
The rest, however, is true - VRDB is not a backup system, the stored information is very small (not the whole files). Besides, only Win32 executables are processed. The VRDB data are stored in \Data\Integ\avast.int