Other OS important property is absence or existence of means of support of the multiprocessor processing in it - multiprocessing. Multiprocessing leads to complication of all algorithms of resource management.
This function includes providing necessary structures of external memory as for data storage, directly entering a DB, and for the office purposes, for example, for acceleration of access to data in certain cases (indexes usually are for this purpose used). In some realization of DBMS possibilities of the existing file systems are actively used, in others work is performed up to the level of devices of external memory. In the developed DBMS users are anyway not obliged to know, whether uses DBMS file system and if uses as files are organized. In particular, DBMS supports own system of a name of objects of a DB.
The major divided resource is processor time. The way of distribution of processor time between several processes which are at the same time existing in system (or threads) in many respects defines specifics of OS. It is possible to distinguish two groups of algorithms from a set of the existing options of realization of multitasking:
It is delivered with a cover for clients: DOS, Macintosh, OS/2, UNIX, Windows (the cover is developed for Windows NT by the Novell company now though Microsoft already realized client part of NetWare in Windows NT)
DBMS usually work with a DB of the considerable size; at least this size usually significantly is more than available volume of random access memory. It is clear that if at the appeal to any element of data the exchange with external memory will be made, all system will work with the speed of the device of external memory. Almost only way of real increase in this speed is buffering of data in random access memory. Thus, even if the operating system makes all-system buffering (as in case of UNIX OS), it is not enough for DBMS which has much bigger information on usefulness of buffering of this or that part of a DB. Therefore in the developed DBMS own set of buffers of random access memory with own discipline of replacement of buffers is supported.
Single-task OS generally carry out function of granting the virtual computer to the user, doing simpler and convenient process of interaction of the user with the computer. Single-task OS include control facilities peripherals, control facilities files, means of communication with the user.