I decided to make a dual-boot dos system, using these versions of DOS.
The dos 7.10 is a largely modified version of the DOS in Win98se, dos 6.30 is the composite 6.20/6.22 build.
In keeping with the effect of installing win2k over win9x, dos7 is stored in c:\msdos7, The other dos is stored in c:\dos. The system is vpc2007. The main aim is to minimise reboots from a raw system. It's down to the fdisk reboot now.
- msdos7 is used to partition the disk, and to install its files. The msdos.sys file copied to the hard drive has already enabled the boot previous dos (at #7 on the menu), and we copy a sample autoexec.dos and config.dos.
- This installation leaves you in c:\msdos7, from where we insert a second dos diskette, and run instdos.bat from dos71. This creates the dos directory, and copies the files from the floppy disk to the hard drive. The msdos.sys and io.sys are copied to msdos.dos and io.dos.
- On reboot, a fully functional dual-boot dos7 / dos6 is working.
MSDOS 7 is running in auto mode, ie no autoexec/config.sys, while MSDOS 6 runs with these files. The generic config files in the msdos7 setup are replaced by a version that installs the utilities needed to break out of the vpc, into dos6.
MSDOS 7 loads a default environment, using %windir%\tmp and %winbootdir% for the sources of the various command files.
Unlike Win95, the hidden name for io.sys in an msdos6 boot is 'jo.sys'. This is the same name used for the boot from this floppy program on the cdrom. So after a previous msdos boot, the root directory contains both jo.sys and io.sys, but the boot sector will find jo.sys first, and load that.
The default environment is all over the place. If both winbootdir and windir are set, then you get:
-----MSDOS.SYS------ [Paths] WinDor=C:\MSDOS7 WinBootDir=C:\MSDOS7 HostWinBootDrv=C -----Bootlog------- LoadSuccess=C:\MSDOS7\HIMEM.SYS LoadSuccess=C:\MSDOS7\IFSHLP.SYS ----Environment---------- TMP=C:\MSDOS7\TEMP TEMP=C:\MSDOS7\TEMP PROMPT=$p$g winbootdir=C:\MSDOS7 PATH=C:\MSDOS7;C:\MSDOS7\COMMAND COMSPEC=C:\MSDOS7\COMMAND.COM
The msdos.sys we're using is a modified version of the ChinaDOS file. It's interesting that while windir is in msdos.sys, it's not in the environment.