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Андрей Щеглов edited this page Jan 23, 2025 · 20 revisions

DOS

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Installation

DOSBox

MS-DOS 6.22 can see no more than 1024 cylinders, which is roughly 504 MB with 16 heads (C/H/S = 1024/16/63) and 8032.5 MB with 255 heads (C/H/S = 1024/255/63). Sector size is assumed to be 512 bytes.

A disk image file of 504 MB (with 16 "heads") can be created using the bximage utility from bochs. A disk image with 255 "heads" can be created using dd:

dd if=/dev/zero of=path/to/hda.img bs=512 count=16450560

Don't forget to make the image file sparse:

fallocate -d path/to/hda.img

MS-DOS can be installed using the following [autoexec] section in dosbox.conf:

[autoexec]
@echo off
imgmount 2 path/to/hda.img -t hdd -fs none -size 512,63,255,1024

rem Install MS-DOS 6.22, Ctrl+F4 to swap floppy images.
boot path/to/disk01.img path/to/disk02.img path/to/disk03.img

Once MS-DOS is installed, be sure to update the boot command arguments:

[autoexec]
@echo off
imgmount 2 path/to/hda.img -t hdd -fs none -size 512,63,255,1024

cls
boot -l c

If extra partitions (D:, E:, F:) are created in the above 8 GB disk (using DOS fdisk), the image file geometry, as reported by Linux fdisk, will be:

Disk hda.img: 7.84 GiB, 8422686720 bytes, 16450560 sectors
Geometry: 255 heads, 63 sectors/track, 1024 cylinders
Units: cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot Start   End Cylinders  Size Id Type
hda.img1   *        1   261       261    2G  6 FAT16
hda.img2          262  1024       764  5.8G  5 Extended
hda.img5          262   522       261    2G  6 FAT16
hda.img6          523   783       261    2G  6 FAT16
hda.img7          784  1024       241  1.8G  6 FAT16

Yet, upon the very next reboot, MS-DOS will either hang or run into a "divide overflow" error. This problem can be worked around: if MS-DOS setup is re-run from the floppy disks, D:, E:, and F: drives can be formatted during the setup process, and MS-DOS reinstalled. A run of scandisk will be required, as some or all logical drives will have missing FAT backup copies and/or lost clusters.

Still, such a multi-partition disk image will be impossible to correctly mount as a Linux loop device:

If you have VirtualBox installed, the disk image can be converted to the VHD format:

vbox-img convert --srcformat=RAW --srcfilename=hda.img --dstformat=VHD --dstfilename=hda.vhd

If the VHD image is attached to a Hyper-V virtual machine running Linux, fdisk will show exactly the same geometry:

Running dosfsck against /dev/sda1 will report bad file name errors, consistently with the mounted FAT16 file system view:

Still, after all file system errors are fixed, an attempt to boot MS-DOS from the disk image will hang:

At the same time, if the above VHD image is converted back to RAW and re-attached to DOSBox, MS-DOS boots just fine, and scandisk reports no further errors. Yet, it may be more practical to use a 2 GB disk image (C/H/S = 261/255/63) and create just a single FAT16 partition:

dd if=/dev/zero of=path/to/hda.img bs=512 count=4192965

Mounting a hard drive image in Linux

The image file may be later mounted as a loop device (assuming codepage 866 is compiled into the kernel, modprobe nls_cp866):

sudo mount -t vfat -o loop,offset=32256,codepage=866,iocharset=utf8,fmask=133,uid=$(id -u),gid=$(id -g) path/to/hda.img mountpoint/

Video drivers

By default, DOSBox emulates S3 Trio64V+ video card. Drivers for Windows 3.x are available.

The driver package from S3 replaces some of the bitmap fonts (*.fon) files shipped with a localized (e.g.: Russian) version of Windows 3.x. This messes up Cyrillic fonts.

Be sure to back up your *.fon files immediately after Windows installation, and restore the fonts once you've installed S3 video drivers.

Configuration files

Initially, a reasonable config.sys might look like this:

device=c:\dos\himem.sys /testmem:off /verbose
dos=high,umb
device=c:\dos\emm386.exe min=0 noems novcpi verbose highscan

buffers=15,0
fcbs=4,0
files=30
switches=/F
lastdrive=Z

devicehigh=c:\dos\setver.exe

country=007,,c:\dos\country.sys
devicehigh=c:\dos\display.sys CON=(EGA,866,1)
installhigh=c:\dos\nlsfunc.exe c:\dos\country.sys

devicehigh=c:\dos\ramdrive.sys 8192 512 1024 /E
devicehigh=c:\dos\ansi.sys

autoexec.bat:

@echo off

prompt $p$g
path c:\dos
set TEMP=c:\tmp

loadhigh c:\dos\smartdrv.exe /X

mode con codepage prepare=((866) c:\dos\ega.cpi)
mode con codepage select=866
chcp 866
loadhigh keyb ru,866,c:\dos\keyboard.sys

loadhigh c:\dos\doskey /insert

After memmaker is run, it adds /L (and, sometimes, /S) arguments to devicehigh, installhigh, and loadhigh commands. config.sys:

device=c:\dos\emm386.exe min=0 noems novcpi verbose highscan I=B000-B7FF X=C800-C9FF

devicehigh /L:1,12048 =c:\dos\setver.exe
devicehigh /L:1,15792 =c:\dos\display.sys CON=(EGA,866,1)

devicehigh /L:1,5888 =c:\dos\ramdrive.sys 8192 512 1024 /E
devicehigh /L:1,9072 =c:\dos\ansi.sys

autoexec.bat:

loadhigh /L:0;2,45456 /S c:\dos\smartdrv.exe /X

loadhigh /L:2,16208 keyb ru,866,c:\dos\keyboard.sys

loadhigh /L:1,6384 c:\dos\doskey /insert

DOS memory explained

EMM386.EXE

Virtual 8086 mode

Virtual 8086 mode is a sub-mode of Protected mode. In short, Virtual 8086 mode is whereby the CPU (in protected mode) is running an "Emulated" 16bit Real Mode machine.

DOS extenders

Programming

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