For mass storage media are referred to in the IT field, to store large amounts of data permanently. Volatile memory as conventional RAM according to this definition, no storage, regardless of their size.
Due to the general development in the computer field is naturally the term " large amount of data " strongly depends on the currently prevailing conditions. Thus is meant by a mass storage disk over time with ever higher capacities. However, the mass storage is through time each larger and slower than the usual memory at the same time. Programs and data on a mass storage are almost never directly manipulated by a main processor, but for this purpose copied ( "loaded" ) where it is processed first into memory. The results can ( "stored" ) are written to the mass storage again when required.
The greatest importance as a mass storage have hard drives for over twenty years. The development of their capacity has kept pace with the overall development: In the early 1980s they were 10 megabytes, today they can save several thousand gigabytes. Your speed is also increased significantly, but not to the same extent as their capacity.
Depending on the size definition media such as punch cards, paper tape, magnetic tapes, floppy disks, optical disks ( including read-only CD -ROM, DVD-ROM and BD-ROM and the mono - or rewritable variants) and flash memory media like USB sticks also classified and Compact Flash cards as mass storage. Their advantage is the easy mobility and usability as a removable disk in any device with a corresponding drive slot or matching interface.
In general, in mass storage not only the capacitance of interest, but depending on the application and the following factors:
- Latency: average or maximum length of time elapses from transmission of a data request to the mass storage device to the beginning of a data transfer.
- Flow rate: the amount of data transmitted per unit time.
- Average life: The number of operating hours, to ( statistically ) the first data loss occurs.
- Access type: mass memory can be read or written in the follow-up (following ) or direct access ( optional). Some media can only be written once (see WORM ), and are suitable for archiving. Others are limited rewritable ( CD-RW/DVD-RW ) or indefinite number of times (flash memory, hard drives ). So-called ROM discs are provided in the production of data and can only be read.
- Mobility: Some mass storage are usually permanently installed, and others can be easily replaced.
- Networking: There are several ways to provide mass storage in a computer network. On file servers, which are also known as Network Attached Storage is accessed at file level. In a Storage Area Network accessing data block level. Both types can be integrated into existing networks. Thus, no new hardware has to be installed into existing systems.
- Security: Some mass storage with a private password protection or ways to delete the data stored on them completely and irreversibly, without the mass storage eg having to physically destroyed by shredding. This may be of importance for sensitive data.