DOS 4.1 For the Apple II

Hidden in the wings of the Apple II world has been a gem of an operating system re-build, DOS 4.1. The new DOS is a complete re-work of DOS 3.3 from the perspective of retired Raytheon engineer and former Sierra On-Line developer, Walland Philip Vrbancic.

Changes in DOS 4.1

Included in this new version of DOS, is the ability to have full lowercase commands for all commands, a 24 letter volume name, the ability to include DOS Version and Build type in the VTOC as well as the location in RAM. A high versus a low version of the DOS 4.1 disk allows for a specific loading of the DOS, thus giving the end user more control over where they would like DOS to reside. Also the time stamps on files are more complete in DOS 4.1

DOS 4.1 also includes a number of fixes and changes to DOS 3.3 which were part of the way Apple handled certain aspects such as the I/O Block (IOB). Zero Page usage is slightly altered so as to resolve some of the issues from earlier DOS versions. There are also some modifications to the WOZ rendition of Sweet16.

One of the features which was included with some fervor was the A.P.P.L.E. and Micro 6502 published Garbage Collection routines created by Cornelis Bongers in the early 1980s. These routines allow faster string garbage collection. What Walland changed was is being tied to Ampersoft. A full description of the algorithm used by Bongers and the changes are described in the included manual.

Update 3 Feb 2019: We can now confirm that the programs and emulators that support DOS 4.1 now include:

  • Applewin Emulator
  • Virtual II Emulator
  • Microm8 Emulator
  • DiskBrowser
  • Applesauce
  • More to come….

Source Code for the Programs and DOS 4.1

Along with the complete re-engineering of the operating system comes a host of utility disassembly’s and re-assembly’s allowing source code thought lost to the years to come to life once again. Some of these sources include Big Mac Assembler, Sourceror, File Developer, The Lisa Assembler and several others.

Walland had modified a host of programs to work with DOS 4.1 and has placed each of these Apps on an individual disk along with their source code.

Disks and Manuals

Disk images for DOS 4.1, his programs updated to support 4.1 and source code are available on the Apps page and on Walland’s site

In print for the first time, the hardcopy version features a newly-designed cover, and is over 220 pages. It is available from:

DiskBrowser Updated

On a related note, DiskBrowser is now DOS 4.1 ready. A new version 1.0.33 is available from the DiskBrowser website at:

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About the Author


The A.P.P.L.E. Website is run by the Apple Pugetsound Program Library Exchange Users Group and is open to all Apple and Macintosh fans and their friends.