Main Memory Data Base Management System makes the best use of current hardware and advanced architecture benifits, eg., the emerging large volume memory,massive parallel computer architecture, Client/Server model and network computer. Storing its data in main physical memory to get very high speed access, MMDB validates its use for some on -line or real time applications. Coventional database systems are optimized for the particular characteristics of disk storage mechanisms. MMDB, on the other hand, use different optimizations to structure and organize data, as well as to make it reliable.The major techniques and their usage in some designed or implemented MMDB systems will be surveyed in this paper.