Atari DOS
Atari DOS , short for Atari Disk Operating System , is an operating system for use on Atari 8-bit computers.
Atari disk formats with 90 kB and later also 130 kB of storage space were supported. Diskettes were written and read on one side.
Versions
The best-known versions are DOS II 2.0s from 1980 and 2.5 from 1984. In between, DOS 3.0 was also released, which initially came with the new ATARI 1050 floppy disk drive and was the first to support floppy disks with 130 kB storage capacity. However, it was not accepted by the customer due to its high memory requirements and the resulting lack of compatibility with older software. So DOS 2.5 was released, a DOS 2 with support for 130 kB floppy disks.
Structure and properties
Atari DOS basically consisted of two files:
DOS.SYS offered the functionality for creating, renaming, deleting and reading files as well as formatting floppy disks. These functions could be called by programs using the D: handler (see below ).
DUP.SYS offered menu-driven access to these functions. Additional functions that DOS.SYS did not contain were copying and duplicating files.
When the Atari 130XE came onto the market, a RAM disk driver ( RAMDISK.COM ) was added, which made the computer's additional RAM available as a floppy disk drive.
Files could be named according to the 8.3 convention known from the PC sector , i. H. eight characters for the file name and an additional three characters for the extension, separated by a period. All letters have been converted to capital letters. As of DOS 2.5, the first character in the name could also be a number. This representation has been changed in the table of contents of an Atari floppy disk. Unused characters of the actual name were padded with spaces and the period in front of the file name extension was not displayed. It was not possible to create subdirectories. A maximum of 64 files could be created on a floppy disk, which was quite sufficient given the low storage capacity of the floppy disks.
In order to use an Atari with a floppy disk drive, the Atari DOS had to be loaded when booting . Without booting a floppy operating system, Atari 8-bit computers offered no floppy disk functionality. Due to this fact several DOS versions could be developed for the Atari that were not based on Atari DOS. This resulted in DOS versions which, assuming suitable hardware, could manage data carriers with up to 16 MB and which offered the functionality of subdirectories and even time stamps .
The size of files or the free space was specified in sectors. With the write density used by the Atari DOS, one sector was exactly 128 bytes (later DOS versions used a high memory density of 256 bytes per sector). The last three bytes of a sector formed the sector link. It gave information about the number of data bytes in this sector (usually 125), the file number and the number of the next sector belonging to this file. The exact size of a file in bytes could not be determined directly.
Under DOS 3.0, four sectors were combined into one block . With large files this saved storage space by nine bytes per block (since only the blocks were linked), but small files took up at least one block, i.e. four sectors or 512 bytes (under DOS 2 only 128 bytes) on the data carrier .
The D: handler
Atari disks are addressed via the so-called D: handler . The Atari DOS offered other handlers, such as B. K: (keyboard / keyboard), S: (screen), E: (editor / screen and keyboard). These handlers in Atari DOS are comparable to today's hardware drivers. The D: handler was loaded with DOS. Thus DOS commands could be executed without the menu navigation DUP.SYS (DUP.SYS could be omitted if you wanted to create a bootable floppy disk and want to provide as much storage space as possible). You could rename a file e.g. B. with the command
XIO 32,#1,0,0,"D:altername,neuername"
A maximum of eight floppy disk drives could be connected to the Atari. These were then addressed with D1: to D8:.