Segment registers are used at identification of a segment of memory. The segment is a continuous block of memory, 64 long To. Segment registers are applied in a combination with the register of the index or index registers and in this case identify a concrete cell of memory.
Data input about keyboards and their conclusion to the display screen management of the ANSSYS driver. The ANSSYS file belongs to additional system.. The driver represents the system program which is responsible for communication
Devices of posimvolny transfer of data carry out transfer of information on one symbol for reception. Ports of consecutive and parallel adapters and displays treat these devices. In MS-DOS to each of these devices there corresponds the concrete name (name). The MS-DOS driver can operate only one device of posimvolny transfer. Devices of block transfer of data carry out transfer of information on blocks. Each block as the rule, makes 512 bytes. Disk drives for flexible diskettes, disk drives for the hard drive and other devices for information stores belong to these devices. Devices of block transfer do not possess the concrete name. The MS-DOS driver can serve some devices of the block
Communication of the car with the peripheral device is carried out in strictly certain order. To each peripheral device in operational system there corresponds the program which is responsible for its contact with the computer. These programs are called as DRIVERS.
MS-DOS provides two technologies of service of files. The first was developed at creation of versions X. This technology is based on use of structures of the data called by control units of the file (FCB). At that time the vast majority of kompyyuer worked under control of the CPM operating system. FCB blocks provided a sovmestmost of the MS-DOS files with files of this system. When developing MS-DOS of versions X when the hierarchical structure of the organization of files was offered, the second technology of their service was developed. It is based on use of references to the operating record of the file and does not demand the FCB organization. After this technology was tested on the UNIX operating system, it was widely adopted.
One of the main functions of operational system is a providing group of the efficient drivers available to system and applied programs. If contact with pereferiynym the device is necessary for the working program, it reports to operational system what of devices is necessary for it, and MS-DOS provides it the corresponding driver.
Communication is a soyediineniye of two system programs or teams, teams with the program or on the contrary. Such connection obespechivayetvozmozhnost of transfer of the output data of one program or team other program or team. Distinction between the directed input-output and kommunikatsiyey:napravlenny input-output is a data read-out with or their transfer on the peripheral. Communication is a way of interaction between programs or teams of system (i.e. data transmission happens in an operating system)
Programmatically to address to system function, it is necessary to execute the following: (to write down number of the corresponding function in the register AN; (to write down the parameters necessary for function work, in the corresponding registers; (to cause interruption 21H. At the appeal to interruption 21H, control is transferred by MS-DOS. The operational system determines by value of the register AN, what function has to be carried out. Then from the others (quite certain for each function) registers values of parameters then the demanded function is carried out are read out. MS-DOS places the parameters returned by function in the corresponding registers and returns management in the defiant program. The program looks through registers and makes the analysis of result of performance of function.
In order that data could be written down on a disk, its surface needs to be structured - i.e. to divide into sectors and paths. PATHS is concentric the circles covering a disk surface. To a path number 0, following it - 1, etc. is assigned to the next to edge of a disk. If a diskette bilateral, both of its parties are numbered. Number of the first party - 0, number second -
Record of start checks, whether are the IO.SYS and MSDOS.SYS files the first files on a disk. If result of check positive, files are loaded into memory, and the free site with the youngest address gets out. Then control is transferred to the initializing IO.SYS file module. If files are written down in other place or they are not present on a disk, on the screen there is a message: