This project maintains the sources of DRBIO.SYS, DRDOS.SYS and COMMAND.COM ported to
- the JWasm assembler, version 2.17 or later, and
- the OpenWatcom toolchain, version 1.9 or later.
Binaries and a 1.44M floppy image are built automatically through Github actions. To download them, go to the actions page, and then click the last successful workflow build job. The files are provided under the artifacts section.
The EDR-DOS kernel may be built in different flavors. The historic one consists of two files, DRBIO.SYS and DRDOS.SYS. The new one consists of a single file KERNEL.SYS. The historic one is what gets built by default.
KERNEL.SYS is compatible with the FreeDOS load protocol. It can be used as a drop in for the FreeDOS KERNEL.SYS by replacing it with the EDR KERNEL.SYS. Notice that the kernels are not 100% compatible, especially regarding the drive letter ordering and the expected format of the config.sys files.
I was able to successfully build the kernel and command interpreter under DOS, Win32, Linux and MacOS.
The makefiles expect the following executables to be present:
- jwasm, for DOS it is jwasmr
- wmake
- wlink
- exe2bin
- and wcl if building command.com.
Further, if you build under a UNIX-like operating system, make sure to build
the tools under the ltools/unix directory first by invoking make inside
the directory.
You may build DRBIO.SYS, DRDOS.SYS and COMMAND.COM by calling the OpenWatcom
make utility wmake from the project root directory. The generated binaries
will be placed under the bin directory.
You may instead build the individual components by invoking wmake under the
directory of the components. The built binaries are then placed into the bin
subdirectory for the components, like drbio/bin/drbio.sys.
You may generate uncompressed DRBIO.SYS and DRDOS.SYS binaries by invoking
wmake COMPRESSED=0 from the main directory or the directories of the
components.
You may build a single file version of the kernel by calling the master
makefile via wmake SINGLEFILE=1. The kernel file is named KERNEL.SYS.
The single-file kernel can also be built uncompressed, but then it lacks
the ability to be used as a replacement for FreeDOS KERNEL.SYS. The reason
is that the EDR-DOS kernel lives at segment 70h, while the FreeDOS loader
loads the kernel to 60h. The compressed kernel relocates itself to the
correct segment at the uncompression stage, so the uncompressed kernel
lacks this ability.
After building, make sure that the bin directory contains
- DRBIO.SYS and DRDOS.SYS, or KERNEL.SYS
- COMMAND.COM
- SYS.COM
Under DOS, you may use the provided SYS command to make a bootable disk. To make a bootable floppy, insert a freshly formatted disk into drive A: (you may have to substitute the drive letter).
Then invoke:
SYS A:
from within the directory containing the files mentioned above. The SYS command then copies DRBIO.SYS, DRDOS.SYS and COMMAND.COM onto the floppy and installs a boot loader to make the floppy bootable, or KERNEL.SYS and COMMAND.COM if the single-file kernel was built.
You may also manually copy KERNEL.SYS over to the drive to be booted from and name it DRBIO.SYS. Like so:
SYS A: /BOOTONLY /OEM:EDR
COPY KERNEL.SYS A:\DRBIO.SYS
COPY COMMAND.COM A:\COMMAND.COM
The kernel than utilizes the ordinary EDR-DOS boot protocol, but with DRBIO.SYS being a combined DRBIO / DRDOS file. This also works with an uncompressed KERNEL.SYS.
The provided SYS command is part of the FreeDOS kernel repository The binary was built from this specific commit.
FreeDOS SYS is distributed under the GNU public license.
Under Linux and MacOS, you may invoke sh mkimage.sh under the image
directory. This generates a 1.44M floppy image edrdos.img. Make sure
to build the binaries prior to running this script.
To build a single-file image, invoke sh mkimage.sh singlefile.
The script depends on Mtools and dd being installed.
The code for the installed bootsector comes from FreeDOS.