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HI,
the main distinguishing factor between in-memory database and on disk database is that the commit write acknowledge is received directly from memory instead of disk which makes the operations much faster.
However understand that in memory databases cannot work independently at some point or the other the data residing in memory has to be stored at disk level.
You generally deploy in memory database not for the entire database but just for a few critical tables which require extremely rapid I/O times.
Take a typical stock exchange scenario, when you purchase a share the transaction has to be at a particular share value for that exact second in time, for this you would cache the share price table and the user transaction table in the in-memory database (which sits on top of the traditional database). That is how you receive extremely quick responses for your share purchase transactions, Once the transaction is done, the data in memory is written to disk.
Also the programming language required to commit data in memory is different from traditional sql fired on RDBMS. It generally employs OCI like calls from java or pro C programs.
Oracle Database12C is coming up with a new in memory feature which makes this seperation less complicated and you will be able to address the in memory section of data with traditional sql, plsql.
Look into oracle in memory database or berkeley db for more understanding.
DBMS(Data Base Management System) A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, and the use of the database of an organization and its end users. It allows organizations to place control of organization-wide database development in the hands of database administrators (DBAs) and other specialists. DBMSes may use any of a variety of database models, such as the network model or relational model. In large systems, a DBMS allows users and other software to store and retrieve data in a structured way. It helps to specify the logical organization for a database and access and use the information within a database. It provides facilities for controlling data access, enforcing data integrity, managing concurrency controlled, restoring database. File Processing System. File processing system store data in separate computer files. File processing system is a system used to store and manage data that involves each department or area within an organization having its own set of files, often creating data redundancy and data isolation. File processing system store data in separate computer files Disadvantages of File Processing Systems include: 1. Program-Data Dependence. File descriptions are stored within each application program that accesses a given file. 2. Duplication of Data. Applications are developed independently in file processing systems leading to unplanned duplicate files. Duplication is wasteful as it requires additional storage space and changes in one file must be made manually in all files. This also results in loss of data integrity. It is also possible that the same data item may have different names in different files, or the same name may be used for different data items in different files. 3. Limited data sharing. Each application has its own private files with little opportunity to share data outside their own applications. A requested report may require data from several incompatible files in separate systems. 4. Lengthy Development Times. There is little opportunity to leverage previous development efforts. Each new application requires the developer to start from scratch by designing new file formats and descriptions 5. Excessive Program Maintenance. The preceding factors create a heavy program maintenance load. 6. Integrity Problem. The problem of integrity is the problem of ensuring that the data in the database is accentuate.
