The approach presented in this paper uses VM(virtual memory) techniques of OS to allocate a buffer pool from VM whose size can be equal to the size of the whole VM.The approach is implemented as a C+ + class library that can be linked with an application, requiring no special compiler support. Application program accesses objects via normal VM pointers, and manipulates objects using the same compiled code. Dual-buffer strategy based on this VM technique allows the size of database exceed the size of VM.