7.3.1) What is Atari DOS, and what versions did Atari release?

This FAQ section describes the various DOS versions produced by Atari for use
with their 8-bit computers: DOS I, DOS 2.0S, DOS 3, DOS 2.5, DOS XE, DOS XLE

On the Atari, a complete Disk Operating System (DOS) consists of a complex,
flexible combination of software components provided in the Atari OS on ROM
with software components loaded into RAM from disk:

  1) SIO (Serial I/O bus Utility) routine
      - Component of the Atari OS
      - Generalized low level communications with SIO bus devices, including
        disk drives
      - Utilized by the Resident Diskette Handler
      - Normally utilized by the FMS
  2) Resident Diskette Handler
      - Component of the Atari OS
      - Utilizes SIO for communications with disk drives
      - Supports just five functions (four on the 400/800):
         1. GET SECTOR
             - Read a specified sector
         2. PUT SECTOR WITH VERIFY
             - Write sector; check sector to see if written
         3. STATUS REQUEST
             - Ask the disk controller for its status
         4. FORMAT
             - Issue a format command to the disk controller
         5. PUT SECTOR WITHOUT VERIFY
             - Write sector (don't check sector to see if written)
             - Available on XL/XE; not available on 400/800
      - 400/800: Uses 128 byte sectors
        XL/XE: Can read/write disk sectors having variable length from 1 to
               65536 bytes.  Default=128 bytes
      - Normally only used to load the FMS from disk.  Exception: Atari DOS I
        uses the OS-resident Diskette Handler for all disk communications.
  3) FMS (File Management Subsystem)
      - Must be loaded from disk (using the Resident Diskette Handler)
      - Normally utilizes SIO for disk drive communications
      - Does not utilize the Resident Diskette Handler.  Exception: Atari
        DOS I uses the OS-resident Diskette Handler for all disk
        communications.
      - Normally provides a D: Disk File Manager device handler that is
        compatible with CIO
  4) CIO (Central Input/Output Utility) routine
      - Component of the Atari OS
      - Generalized high level, device independent access to device handlers,
        including any disk drive device handler provided by a FMS
  5) DUP (Disk Utility Package) or equivalent software program(s)
      - Optionally provided with a FMS
      - Must be loaded from disk using the FMS
      - Typically a DOS menu program, but could take any form of software
        that provides a user interface to FMS management functions
      - Normally utilizes CIO for carrying out disk management operations

In practice, those DOS components loaded into memory from disk, that is, a FMS
and any additional programs distributed with that FMS (such as a DUP), are
normally collectively described as a "DOS" on the Atari.

DOS I
-----
DISK OPERATING SYSTEM  9/24/79  COPYRIGHT 1979 ATARI
- Contains two main parts:
    - A File Managememt Subsystem (FMS)
       - Developed by Paul Laughton (also wrote: Atari BASIC) for Shepardson
         Microsystems, Inc. (SMI) for Atari
    - A Disk Utility Package (DUP)
- Shipped with 810 disk drives manufactured from 1980-1981.
- Disk Utility Package (DOS menu) is loaded into memory with the FMS
- Uses the OS-resident Diskette Handler for all disk communications via SIO
- Disk drive type supported: Atari 810 (& compatible)
- Disk utilization/filesystem: "DOS I"
    - 128 total bytes/sector, with 3 bytes of each sector used to address
      the next sector
    - 40 tracks * 18 sectors/track = 720 total sectors, with 11 sectors used
      for software control or unused by the FMS.
    - Data capacity per diskette:
      709 sectors  x  125 bytes/sector  =  88,625 bytes/disk
    - Cannot read disks written with DOS II, which require a 3 sector boot
    - 11 special sectors:
            1 Boot sector, containing the boot record accessed by the Atari OS
              at system power-up
          360 Volume Table of Contents (VTOC) (sector usage)
      361-368 File Directory (8 directory entries per sector)
          720 unused by the FMS (FMS interprets the VTOC sector bit map as
              sectors numbered 0-719, ignoring nonexistant sector 0, while the
              Atari 810 drive uses sectors numbered 1-720)
    - Maximum of 64 files per diskette (8-sector File Directory)
- Uses binary file format unsupported by any other DOS version for the Atari
- D: Disk File Manager supports up to four 810 disk drives, D1: through D4:
    - To configure DOS I for fewer drives (freeing system environment RAM),
      adjust memory location 1802 ($70A or DRVBYT):
       1. Boot the system to the BASIC READY prompt
       2. Enter one of:
           - POKE 1802,1    (for a one drive system; saves 397 bytes)
           - POKE 1802,3    (for a two drive system, saves 258 bytes)
           - POKE 1802,7    (for a three drive system, saves 130 bytes)
           - POKE 1802,15   (for a four drive system; DOS I default value)
       3. Go to DOS and use menu item H (WRITE DOS FILE) to write the DOS.SYS
          file (with the new value of location 1802) to disk, replacing any
          existing copy of DOS on that disk.
- Can open up to 3 files simultaneously
    - Configurable by adjusting memory location 1801 ($709 or SABYTE) via
      the same process as described for adjusting the number of disk drives.
      Valid values for DOS I are 1-3 inclusive.  Default is 3.
- AUTO.SYS can be used to automatically poke data in RAM locations on
   system startup.
- Files copied or duplicated in small buffer
- Must redisplay menu before issuing new command
- Can only write DOS system file to drive 1
- N. DEFINE DEVICE menu option: "The full implementation of this selection is
   not supported, so use it with caution." --DOS Reference Manual p.39
- DOS I is not compatible with the 850 Interface Module R: device handler
- Disk File Manager Master Copy (CX8101) disk contains:
    DOS.SYS  both the FMS with D: Disk File Manager and DUP with DOS Menu,
             loaded by OS-resident Diskette Handler on system startup
- Manual: Disk Operating System Reference Manual C015200

DOS 2.0S
--------
DISK OPERATING SYSTEM II VERSION 2.0S  COPYRIGHT 1980 ATARI
- Shipped with 810 and 1050 disk drives manufactured from 1981-1983. 
   Master Diskette also shipped with the Atari Touch Tablet.
- FMS (DOS.SYS) component developed by Paul Laughton for Shepardson
   Microsystems, Inc. (SMI) for Atari, based on the Atari DOS I FMS.
   Released code version: "19-Aug-80"
- Disk Utility Package (DUP.SYS -- DOS menu) is separate from the FMS, and
   optional for use of the FMS, freeing up memory for user programs when the
   DUP is not needed.  Released code version: "ver 2.9  11/18/80"
- Does not use the OS-resident Diskette Handler once the FMS is loaded.
- Utilizes SIO for disk drive communications
- MEM.SAV file can be employed to preserve the contents of memory to disk
   when DUP.SYS is loaded.
- Introduces support for AUTORUN.SYS binary file launch upon system boot
   (replaces AUTO.SYS of DOS I)
- Disk drive type supported: Atari 810 (& compatible)
- Disk utilization/filesystem: "DOS 2.0 Single Density"
    - 128 total bytes/sector, with 3 bytes of each sector used to address
      the next sector
    - 40 tracks * 18 sectors/track = 720 total sectors, with 13 sectors used
      for software control or unused by the FMS.
    - Data capacity per diskette:
      707 sectors  x  125 bytes/sector  =  88,375 bytes/disk
    - Requires a 3 sector boot (provision for double density version DOS 2.0D)
    - 13 special sectors:
          1-3 Boot sectors, containing the boot record accessed by the Atari
              OS at system power-up
          360 Volume Table of Contents (sector usage)
      361-368 File Directory (8 directory entries per sector)
          720 unused by the FMS (same as DOS I)
    - Maximum of 64 files per diskette (8-sector File Directory)
    - Difference in boot record lengths means DOS I and DOS II disks cannot be
      interchanged.
- Established standard binary file format supported by ALL other DOS versions
   for the Atari (exception: Atari DOS I)
- By default, the CIO-compatible D: Disk File Manager supports up to two 810
   disk drives, D1: and D2:
    - To configure DOS 2.0S for the number of 810 disk drives attached to the
      system (which affects system environment RAM), adjust memory location
      1802 ($70A or DRVBYT):
       1. Boot the system to the BASIC READY prompt
       2. Enter one of:
           - POKE 1802,1    (D1:)
           - POKE 1802,3    (D1: and D2: -- DOS 2.0S default value)
           - POKE 1802,7    (D1:, D2:, D3:)
           - POKE 1802,15   (D1:, D2:, D3:, D4:)
           - POKE 1802,31   (D1:, D2:, D3:, D4:, D5:)
           - POKE 1802,63   (D1:, D2:, D3:, D4:, D5:, D6:)
           - POKE 1802,127  (D1:, D2:, D3:, D4:, D5:, D6:, D7:)
           - POKE 1802,255  (D1:, D2:, D3:, D4:, D5:, D6:, D7:, D8:)
       3. Go to DOS and use menu item H (WRITE DOS FILES) to write the DOS
          system files (with the new value of location 1802) to disk,
          replacing any existing copy of DOS on that disk.
- By default, can open up to 3 files simultaneously
    - Configurable by adjusting memory location 1801 ($709 or SABYTE) via
      the same process as described for adjusting the number of disk drives.
      Valid values for DOS 2.0S are 1-7 inclusive.  Default is 3.
- Files copied or duplicated into buffer which can be as large as user memory
   area
- SAVE BINARY FILE has "/A" option allowing two files to be appended together
- Can create load-and-go type file which enables you to select a file and
   have it automatically run without entering a RUN address
- Diskette with bad sectors detected cannot be formatted
- Screen margins are reset when DUP is entered
- DUP: May enter another command or resdisplay menu after a command
- Can write DOS files to any drive
- NOTE/POINT are available for random file access
- Atari 810 Master Diskette II or Atari 810/1050 Master Diskette II (CX8104)
   disk contains:
       DOS.SYS      FMS with D: Disk File Manager, loaded by OS-resident
                    Diskette Handler on system startup
       DUP.SYS      Disk Utility Package (DOS menu)
       AUTORUN.SYS  Loads the R: device handler from an 850 Interface Module
- Shipped with one Atari CX8111 Formatted Diskette II
- Manuals:
    - Disk Operating System II Reference Manual C016347
    - Disk Utilities Listing, February 1981 C016558 (without binder)
      (DUP.SYS source code, early release)
    - DOS Utilities Source Listing (DOS II), August 1981 C017894
      ("Disk Utility Programs (DUP)  ver 2.9  11/18/80")
    - Atari 810 Disk Drive: An Introduction to the Disk Operating System
      C060054 (CO60054)
    - Atari 1050 Disk Drive: An Introduction to the Disk Operating System
      C061529
- On February 25, 1981, the source code to the Atari DOS 2.0S FMS (DOS.SYS)
   was purchased from SMI by Optimized Systems Software (OSS), headed by
   former SMI employees Bill Wilkinson and Mike Peters.
- Inside Atari DOS (Compute! Books, 1982, 0-942386-02-7), authored by
   Bill Wilkinson, made the source code to the Atari DOS 2.0S FMS (DOS.SYS)
   available to the public.  See: http://www.atariarchives.org/iad/
- Modified versions of DOS 2.0S were widely created and exchanged among Atari
   users.  Also notably, the first 3rd-party disk drive for the Atari, the
   Percom RFD40-S1, was initially (1982) distributed with a program ("BLD")
   to build Percom DOS 2.0P (double density support) from a copy of DOS 2.0S.

DOS 3
-----
Atari DOS 3  Copyright 1983
- Shipped with 1050 disk drives manufactured from 1984 through early 1985.
- Developed by 3-person team at Atari, led by Richard K. (Hud) Nordin
    - Project started at Atari by early 1981 under systems software manager
      Brian Johnston.  Contributor: NEOTERIC consultant Harry B. Stewart
- Disk drive types supported:
    1) Atari 810 (& compatible)
    2) Atari 1050 (& compatible)
    3) Atari 1450XLD built-in (double-sided, enhanced/dual density)
       Minimal support only: A single 1450XLD disk drive appears to DOS 3 as
       two Atari 1050 drives.  That is, side 1 is accessed as D1: and side 2
       is accessed as D2:.
- Disk utilization/filesystems:
    1) "DOS 3 Single Density"
       - Sector = 128 bytes
       - Block = 8 sectors = 1024 bytes
       - Track = 18 sectors = 2304 bytes
       - Disk contains 40 tracks, or 720 sectors, or 90 blocks, with 3 blocks
         used for software control.
       - Data capacity per diskette:
         87 blocks  x  1024 bytes/block  =  89,088 bytes/disk
       - Blocks 1-3 are used by the system as 24 special sectors:
             1-9 Boot sectors, containing the boot record accessed by the
                 Atari OS at system power-up
           10-15 unused
           16-23 File Directory
              24 File Allocation Table (block usage)
       - Maximum of 63 files per diskette (8-sector File Directory)
    2) "DOS 3 Double Density" (enhanced/dual density)
       - Sector = 128 bytes
       - Block = 8 sectors = 1024 bytes
       - Track = 26 sectors = 3328 bytes
       - Disk contains 40 tracks, or 1040 sectors, or 130 blocks, with 3
         blocks used for software control.
       - Data capacity per diskette:
         127 blocks  x  1024 bytes/block  =  130,048 bytes/disk
       - Blocks 1-3 are used by the system as 24 special sectors:
             1-9 Boot sectors, containing the boot record accessed by the
                 Atari OS at system power-up
           10-15 unused
           16-23 File Directory
              24 File Allocation Table (block usage)
       - Backward compatible with DOS 3 Single Density
       - Maximum of 63 files per diskette (8-sector File Directory)
- Keyboard Command Processor (KCP) is separate from the FMS, and optional for
   use of the FMS, freeing up memory for user programs when the KCP DOS
   subfunctions and the DOS menu are not needed.
- KCP Overlay (DOS menu) is separate from the FMS and KCP, and optional for
   use of the FMS and KCP, freeing up memory for user programs when the DOS
   menu is not needed.
- MEM.SAV file can be employed to preserve the contents of memory to disk
   when the KCP Overlay (DOS menu) is loaded.
- Supports AUTORUN.SYS binary file launch upon system boot
- File manager and buffers now take up less space than the DOS 2 equivalents.
   All utilities, such as COPY, INIT, DUPLICATE (all UTL files) are called
   into memory only as needed.  Each is maintained in a separate file.
- Provides a direct method for the user to modify the FMS parameters
- Provides an online HELP feature
- Compared to DOS 2: The NOTE and POINT commands return a pointer number
   relative to the start of a file (byte 0) rather than an absolute sector and
   byte location within the sector.
- Master Diskette 3 (DX5052) contains:
    FMS.SYS      FMS with D: Disk File Manager, loaded by OS-resident
                 Diskette Handler on system startup.  Contains subfunctions:
                 ERASE FILE, RENAME FILE, PROTECT FILE, UNPROTECT FILE, LOAD
    KCP.SYS      Keyboard Command Processor, loaded on system startup if a
                 cartridge is present.  Contains subfunctions: SAVE,
                 GO AT HEX ADDRESS, TO CARTRIDGE, COPY FILE, INIT DISK,
                 DUPLICATE DISK, ACCESS DOS 2
    KCPOVER.SYS  KCP Overlay, displays the DOS menu and process commands
    COPY.UTL     COPY/APPEND utility
    DUPDISK.UTL  DUPLICATE utility
    INIT.UTL     INIT Disk utility
    CONVERT.UTL  ACCESS DOS 2 utility, use to copy files from a DOS 2.0S disk
                 to a DOS 3 disk
    HELP.UTL     HELP utility
    HELP.TXT     Text information displayed by the HELP utility
    HANDLERS.SYS Loads the R: handler from an Atari 850 Interface Module
                 during system boot up, if this file is on the drive 1
                 diskette.
- Manuals for DOS 3:
    - Atari Disk Operating System Reference Manual C062287 (100 pages)
      (makes no mention of the 1450XLD built-in disk drive(s))
    - An Introduction to the Atari Disk Operating System C062288 (29 p)
      (makes extensive mention of the 1450XLD built-in disk drive(s))
    - Atari DOS 3 Reference Manual Errata, 05/01/84
   "Early versions of DOS 3 used a random access method that was incompatible
    with large files.  To determine if you have an early version, boot your
    copy of DOS 3 with Atari BASIC, and execute the following BASIC command:
             PRINT PEEK(1816)
    If the value returned is '53', your copy of DOS 3 is the latest released.
    If the value returned is '51' or '56', Atari Customer Relations offered a
    program to update DOS 3 to the latest revision level."
    - Atari 1050 Disk Drive: An Introduction to the Atari Disk Operating
      System C024323 (international; 144 pages)

DOS 2.5
-------
DISK OPERATING SYSTEM II VERSION 2.5  COPYRIGHT 1984 ATARI CORP.
- Shipped with 1050 disk drives manufactured in fall 1985, and with XF551
   disk drives manufactured in 1987-1988.
- Developed by Optimized Systems Software (OSS - Bill Wilkinson) for Atari
- Disk drive types supported:
    1) Atari 810 (& compatible)
    2) Atari 1050 (& compatible)
    3) Atari 130XE RAMdisk (65,408 bytes)
- Disk utilization/filesystems supported (detected automatically):
    1) DOS 2.0 Single Density
    2) "DOS 2.5 Enhanced Density" (or just "DOS 2.5")
        - 128 total bytes/sector, with 3 bytes of each sector used to address
          the next sector
        - 40 tracks * 26 sectors/track = 1040 total sectors, with 30 sectors
          used for software control or unused by the FMS.
        - Data capacity per diskette:
          1010 sectors  x  125 bytes/sector  =  126,250 bytes/disk
        - 30 special sectors:
                1-3 Boot sectors, containing the boot record accessed by the
                    Atari OS at system power-up
                360 Volume Table of Contents (sectors 1-719 usage)
            361-368 File Directory (8 directory entries per sector)
                720 unused by the FMS (same as DOS I and DOS 2.0S)
               1024 Extended Volume Table of Contents (sectors 720-1023 usage)
          1025-1040 unused by the FMS (FMS uses a 10-bit sector address)
        - Maximum of 64 files per diskette (8-sector File Directory)
        - Backward compatible with DOS 2.0 Single Density
    3) "DOS 2.5 130XE RAMdisk"
        - 128 total bytes/sector, with 3 bytes of each sector used to address
          the next sector
        - 508 total sectors, with 9 sectors used for software control.
        - Data capacity:
          499 sectors  x  125 bytes/sector  =  62,375 bytes
        - 9 special sectors:
               360 Volume Table of Contents (sector usage)
           361-368 File Directory
        - Maximum of 64 files (8-sector File Directory)
        - Backward compatible with DOS 2.0 Single Density
- RAM memory locations 1802 ($70A or DRVBYT, the active drive map) and 1801
   ($709 or SABYTE, the maximum number of concurrently open files) are
   utilized in the same way as by DOS 2.0S.
    - If the DOS 2.5 130XE RAMdisk is enabled, the default value for SABYTE is
      131, enabling D1:, D2:, and D8:, where D8: is the RAMdisk.
- DOS 2.5 (DX5075) disk contains:
    DOS.SYS      FMS with D: Disk File Manager, loaded by OS-resident
                 Diskette Handler on system startup
    DUP.SYS      Disk Utility Package (DOS menu)
    RAMDISK.COM  If present on startup disk on an XL/XE with 128KiB RAM or
                 more:
                  1) Displays a message that it is initializing the RAMdisk
                  2) Sets up a 64KiB RAMdisk as D8:
                  3) Copies DUP.SYS to D8: and establishes MEM.SAV on D8:
    SETUP.COM    External utility has 3 functional options:
                  1) Change current drive number
                  2) Change system configuration.  3 configurable options:
                     i) Active drives number (1 to 4)
                     ii) Max number of simultaneous files (1-7)
                     iii) Disk writes with or without verify
                  3) Create an AUTORUN.SYS that does either one or both of:
                     - Load the R: handler from an Atari 850 Interface Module
                     - Load and RUN a BASIC program from the boot disk
    COPY32.COM   Utility to copy files from a DOS 3 disk to a DOS 2.5 or to a
                 DOS 2.0S disk
    DISKFIX.COM  DiskFix Utility can be used to:
                  - Unerase a file (under certain circumstances)
                  - Verify the soundness of every file on a disk
                  - Rename a file by number (solves problem of files with
                    duplicate names)
- Manuals:
    - Atari DOS 2.5: 1050 Disk Drive Owner's Manual C072033
    - Atari DOS 2.5: XF551 Disk Drive Owner's Manual C033537

DOS XE
------
DOS XE DISK OPERATING SYSTEM  COPYRIGHT 1988 ATARI CORP.  VERSION 01.00
- Shipped with late production XF551 disk drives starting in 1989
- Developed by Bill Wilkinson for Atari.  Known as "ADOS" prior to release
- Requires an XL/XE; does not run on the 400/800
- Disk Utility Package (DOS menu) is loaded into memory with the FMS
- Disk drive types supported:
    1) Atari 810 (& compatible)
    2) Atari 1050 (& compatible)
    3) Atari XF551 -- XF551 high speed supported
    4) Atari 130XE RAMdisk (64KiB)
    5) SSDD 5.25" Single-Sided, Double Density
- Disk utilization/filesystems:
    1) "DOS XE" via the native D: Disk File Manager:
        - Supports disk drive sizes up to 16MiB.
        - Files can be up to 8MiB long.
        - All disks are addressed in 256 byte sectors.  Simulates 256 byte
          sectors on 810 and 1050 disk drives, which have 128 byte sectors,
          by reading and writing sector pairs.
        - Up to 65536 sectors can exist on a single disk.
          (65536 sectors x 256 bytes/sector = 16MiB)
        - Five different types of sectors:
           1) Boot sectors
               - Disk sectors 1-3 contain the boot record accessed by the
                 Atari OS at system power-up. (OS reads 128 bytes/sector)
               - Contains a 32 byte Drive Table describing the physical and
                 logical layout of the disk.
               - The DOS XE 130XE RAMdisk does not have boot sectors.
           2) Volume Table of Contents (VTOC) sectors
               - Starts in sector 4 (one sector only for drive types supported
                 by DOS XE).
               - The first 10 bytes give information about the current status
                 of the disk and the rest is a bit map of the blocks on the
                 disk.
           3) Directory sectors
               - The first directory block immediately follows the VTOC
                 sector(s).  Additional directory blocks are allocated as
                 needed and may be scattered throughout the disk, linked by a
                 two-byte pointer at the end of each block.
               - Each entry contains the file name, information about the
                 file (including creation date and last modified date), and up
                 to 12 two-byte pointers which point to the file map blocks
                 for the file.
               - Includes a six byte sector label, containing the File ID
                 number, Volume number, and Sequence number.
           4) File Map sectors
               - Contain from 1 to 125 two byte data block pointers.
               - Includes a six byte sector label, containing the File ID
                 number, Volume number, and Sequence number.
           5) Data sectors
               - 250 bytes allocated for data.
               - Includes a six byte sector label, containing the File ID
                 number, Volume number, and Sequence number.
    2) DOS 2.0 Single Density via the optional DOS 2.x A: Disk File Manager
    3) DOS 2.5 Enhanced Density via the optional DOS 2.x A: Disk File Manager
- Disk File Managers can address up to eight drives (D1: to D8:, A1 to A8:).
- A directory or subdirectory can hold up to 1250 files or subdirectories.
- File pathnames are limited to 80 characters.
- Hybrid interface is both menu driven and command driven, including stacked
   command entry.
- Batch files can be used to automate tasks;
   AUTOEXEC.BAT run automatically when DOS XE is booted.
- RAM memory locations 1802 ($70A or DRVBYT, the active drive map) and 1801
   ($709 or SABYTE, the maximum number of concurrently open files) are
   utilized in the same way as by DOS 2.0S and DOS 2.5.
- DOS XE Master Diskette (DX5090) contains:
    DOSXE.SYS     FMS with D: Disk File Manager, loaded by OS-resident
                  Diskette Handler on system startup
    DOS2.SYS      A: Disk File Manager for DOS 2.x filesystem support
    SETUP.COM     External setup utility.  Configures:
                   - The number and type of drives
                   - The number of file buffers
                   - Installation of the 130XE RAMdisk
                   - Whether the RS-232 handler should be loaded automatically
                     on system startup
                   - Whether a BASIC program should be run automatically
                     on system startup
    RDRIVER.SYS   Used by DOS XE to load R: handler from 850 interface
    COPY3_XE.COM  DOS 3 to DOS XE copy program
    WELCOME.BAS   Sample program provided for experimentation with SETUP.COM
- Manual: Atari DOS XE: XF551 Disk Drive Owner's Manual C300557

DOS XLE
-------
DOS II Version XLE ("DOS XLE") (P) 1990 Atari (Germany)
  Andreas Koch writes (January 2010):
   "programmed by Reitershan in 1990 (as requested by Atari Deutschland then
   for the XF551 drive), it is not only similar, but fully compatible to
   Turbo-DOS XL/XE (also by Reitershan).  It uses the well-familiar DOS 2.5
   DUP-menu, with a few enhancements, like e.g. 1-8 for Dir. of drive 1-8,
   formats 90KiB-360KiB and RAMdisks up to 256KiB; there is even an option (P)
   to switch back to standard DOS 2.5; this DOS has been written with the
   source-code of DOS 2.5 (made available for Reitershan by Atari
   Deutschland), so it is as compatible as possible to DOS 2.5 but still
   offers some enhancements; luckily all Turbo-DOS XL/XE utilities can be used
   with this DOS (e.g. the RAMdisk-driver from Turbo-DOS!);
About Us - Contact - Credits - Powered with Webdev - © Atarimania 2003-2018