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# 2025-02-22 - Install SvarDOS In Virtual Machine |
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I recently read an article about SvarDOS: |
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SvarDOS: DR-DOS Is Reborn As Open Source Operating System |
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DR-DOS on Wikipedia |
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SvarDOS web page |
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I installed SvarDOS both on real hardware and in two virtual |
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machines, and it went pretty well. I loved the minimal but highly |
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functional default configuration. |
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In this log entry, i will walk through the process of installing |
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SvarDOS in qemu and dosbox-x running on Slackware64 15.0. I am |
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using dosbox-x-2025.02.01 and qemu-9.2.0, which are the latest |
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versions from SlackBuilds at the time of writing this log entry. |
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I also use kpartx from multipath-tools to mount the disk images. |
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dosbox-x-2025.02.01 SlackBuild |
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qemu-9.2.0 SlackBuild |
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multipath-tools-0.8.7 SlackBuild |
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Download the SvarDOS stable build (20240915) and package ISO. |
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SvarDOS 1.44M floppy disk |
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SvarDOS package repository ISO |
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I placed these in ~/dist/dos/os/svardos/20240915/ and unzipped the |
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floppy image. |
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# Install SvarDOS using Qemu |
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SvarDOS supports FAT32, but i avoid it because it can be |
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pathologically slow to repair using the free dosfsck.exe. I accept |
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the limitations of FAT16B as a trade-off for better compatibility and |
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maintenance. This limits partition sizes to 2G using the SvarDOS |
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installer. |
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There's a lot of FAT filesystem lore on the Internet. For example, i |
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read that keeping the partitions slightly under 1G results in a |
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smaller cluster size, which greatly reduces disk space overhead, |
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resulting in more space available for data. Since i am using a |
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virtual machine with practically limitless storage, i consider this |
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a micro-optimizations. |
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Below is a table of FAT16 cluster size vs disk space efficiency. |
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Cluster Size Efficiency FAT16 Partition Size |
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------------ ---------- -------------------- |
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2K 98.4% 0-127 MB |
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4K 96.6% 128-255 MB |
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8K 92.9% 256-511 MB |
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16K 85.8% 512-1023 MB |
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32K 73.8% 1024-2047 MB |
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64K 56.6% > 2047 MB |
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http://www.project9.com/fat32/ |
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I believe Windows NT could format FAT16 partitions up to 8G using 64K |
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cluster sizes, but DOS was limited to 2G using 32K clusters. |
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* * * |
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Later in these instructions i answer "Y" to permit fdisk to create a |
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partition with the maximum size. With the 2G disk image, this uses |
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a 32K cluster size, which is compatible with other versions of DOS. |
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With a larger disk, it might use a 64K cluster size, which is |
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not compatible with some versions of DOS. I might need to answer "N" |
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and enter 2000 as the partition size, to keep the partition under 2G. |
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I can verify the cluster size of a FAT16 filesystem using the |
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CHKDSK command. |
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C:\>chkdsk c: /s | find "every cluster" |
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32.768 bytes in every cluster |
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32.768 means the c: drive has the more compatible 32K cluster size. |
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* * * |
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My first DOS hard disk was 80M. In comparison, 2G should be more than |
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enough. I use the raw disk image format for maximum compatibility |
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with various virtual machine software. I use a sparse file to |
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conserve space on the host system. |
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$ mkdir -p Qemu/svardos |
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$ cd Qemu/svardos |
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$ truncate -s 2G svardos.raw |
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The last truncate command creates the 2G sparse raw disk image. |
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Note, I didn't have to use the truncate command! Alternatives |
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are the dd or fallocate commands. |
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* dd if=/dev/zero of=svardos.raw bs=1 count=0 seek=2G |
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* fallocate -l 2G svardos.raw |
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Create a shell script and run it to start qemu. I use new-style qemu |
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configuration options rather than the easier compatibility options. |
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This allows a greater degree of control. |
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$ cat >qemu-svardos.sh <<__EOF__ |
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#!/bin/sh |
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DISK="/home/ben/Qemu/svardos/svardos.raw" |
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CDROM="/home/ben/dist/dos/os/svardos/20240915/sv-repo.iso" |
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FLOPPY="/home/ben/dist/dos/os/svardos/20240915/disk1.img" |
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MACH="pc-i440fx-9.2,dump-guest-core=off,mem-merge=off,usb=off" |
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SAND="on,obsolete=deny,elevateprivileges=deny,spawn=deny" |
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SAND="${SAND},resourcecontrol=deny" |
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SDL_AUDIODRIVER=alsa qemu-system-i386 \ |
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-accel kvm \ |
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-machine "$MACH" \ |
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-machine pcspk-audiodev=1 \ |
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-overcommit mem-lock=off \ |
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-no-user-config \ |
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-sandbox "$SAND" \ |
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-msg timestamp=on \ |
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-cpu max \ |
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-m 32M \ |
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-global i8042.kbd-throttle=on \ |
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-audiodev alsa,id=1 \ |
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-device sb16,audiodev=1 \ |
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-device VGA \ |
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-drive format=raw,file="$FLOPPY",if=none,id=floppy1 \ |
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-device floppy,unit=0,drive=floppy1 \ |
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-global isa-fdc.bootindexA=0 \ |
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-drive format=raw,file="$DISK",if=none,id=disk1 \ |
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-device ide-hd,drive=disk1,bootindex=1 \ |
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-drive file="$CDROM",media=cdrom,if=none,id=cd1 \ |
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-device ide-cd,drive=cd1,bootindex=2 \ |
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-display sdl,gl=on,grab-mod=rctrl \ |
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-rtc base=localtime |
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__EOF__ |
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$ chmod a+rx qemu-svardos.sh |
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$ ./qemu-svardos.sh |
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At the welcome screen, I press Enter to select English. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the keyboard layout screen, I press Enter to select English (US). |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the installation screen, I press Enter to Install SvarDOS. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the partition screen, I select Run the FDISK partitioning tool, |
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then press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At FDISK introduction, I press N to disable FAT32, |
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then press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At FDISK Options, I press Enter to Create DOS partition or |
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Logical DOS Drive. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At Create DOS Partition or Logical DOS Drive, I press 1 to |
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Create Primary DOS Partition, then press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At Create Primary DOS Partition, I press Enter to use the maximum |
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available size for a Primary DOS Partition and make the partition |
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active. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the partition screen, I press ESC to continue. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At FDISK Options, I press ESC to exit FDISK. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At You MUST restart your system for your changes to take effect, |
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I press ESC to exit FDISK. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At Your computer will reboot now, I press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the welcome screen, I press Enter to select English. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the keyboard layout screen, I press Enter to select English (US). |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the installation screen, I press Enter to Install SvarDOS. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the disk screen, I press Enter to select C: [2047 MiB, hda0] |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the format screen, I press Enter to Format drive C: |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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At the installation of SvarDOS to C: screen, I press Enter |
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to Install SvarDOS. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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It installs 32 packages. When it is done, it shows a screen |
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Your computer will reboot now. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I close the QEMU window to power off the virtual machine. |
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This is equivalent to turning off the power while a PC is running. |
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By default, SvarDOS does synchronous I/O and does not use a cache. |
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When at the prompt, the data is already written to disk, so it is OK |
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to abruptly power off the machine. |
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I edit the shell script to make the floppy the last boot option. |
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$ ed qemu-svardos.sh |
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1798 |
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/bootindexA/s/=0/=9/ |
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w |
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1798 |
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q |
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I run the shell script to start qemu again: |
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$ ./qemu-svardos.sh |
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It takes a moment to do the post-install steps. When finished, |
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it shows SvarDOS has been installed. Restart your computer now. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I run FDAPM to do a cold boot. |
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C:\TEMP>\SVARDOS\FDAPM COLDboot |
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It boots to the Welcome to SvarDOS screen. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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The first thing i would like to do is enable access to the optical |
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drive. Unfortunately, the driver is not included on the install |
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floppy. I will need to copy it in place from the Linux host. I |
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close the QEMU window to power off the virtual machine. |
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I create scripts to mount and unmount the disk image on the Linux |
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host. My uid and gid are both 1000. Adjust the script to match |
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yours. |
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$ cat >mount-svardos.sh <<__EOF__ |
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#!/bin/sh |
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disk="/home/ben/Qemu/svardos/svardos.raw" |
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log="/mnt/fuse/svardos.log" |
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dir="/mnt/svardos" |
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part="1" |
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# truncate log |
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cat /dev/null >"$log" |
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losetup -f "$disk" |
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# wait a second, then probe the partitions |
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sleep 1 |
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loop=$(losetup -j "$disk" | cut -d : -f 1) |
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kpartx -av "$loop" >"$log" 2>&1 |
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# find the loop device |
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loopdev=$(awk -v p=$part ' |
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/^add map / { |
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i++ |
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parts[i] = $3 |
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} |
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END { |
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print parts[p] |
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}' "$log") |
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loopdev="/dev/mapper/$loopdev" |
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# mount it |
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mount -o uid=1000,gid=1000 "$loopdev" "$dir" |
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__EOF__ |
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$ chmod a+rx mount-svardos.sh |
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$ cat >unmount-svardos.sh <<__EOF__ |
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#!/bin/sh |
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disk="/home/ben/Qemu/svardos/svardos.raw" |
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dir="/mnt/svardos" |
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# unmount the filesystem |
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umount "$dir" |
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# find loop device |
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loop=$(losetup -j "$disk" | cut -d : -f 1) |
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# detach loop device |
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kpartx -d "$loop" |
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losetup -d "$loop" |
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__EOF__ |
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$ chmod a+rx unmount-svardos.sh |
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To actually mount this disk image, i need to run these scripts as |
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user root. The first time around i need to create directories for |
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the mount point and log file. |
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$ su - |
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# mkdir -p /mnt/svardos |
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# mkdir -p /mnt/fuse |
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Next i mount the disk image, the package ISO, copy the CD driver |
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package, unmount everything, and exit the root shell. |
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# /home/ben/mount-svardos.sh |
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# mount -o loop,ro -t iso9660 \ |
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/home/ben/dist/dos/os/svardos/20240915/sv-repo.iso /mnt/cdrom |
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# cp /mnt/cdrom/videcdd.svp /mnt/svardos/ |
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# umount /mnt/cdrom |
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# /home/ben/unmount-svardos.sh |
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# exit |
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I boot SvarDOS to the welcome screen again. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I install the CD driver packages. |
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C:\>pkg install videcdd.svp |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I use the excellent SVED editor to enable the CD driver in CONFIG.SYS. |
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C:\>copy CONFIG.SYS CONFIG.BAK |
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C:\>sved CONFIG.SYS |
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I use the arrow keys to navigate to the ;DEVICE=C:\DRIVERS\VIDECDD... |
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line. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press Backspace to delete the leading ; character, uncommenting line |
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DEVICE=C:\DRIVERS\VIDECDD\VIDE-CDD.SYS /D:SVCD0001 |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press Esc to open the SVED menu, press Down to select Save, and |
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press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press Esc to open the SVED menu, press Up to select Quit, and |
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press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I use SVED to enable the CD driver in AUTOEXEC.BAT. |
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C:\>copy AUTOEXEC.BAT AUTOEXEC.BAK |
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C:\>sved AUTOEXEC.BAT |
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I use the arrow keys to navigate to the REM SHSUCDX ... line. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press the Backspace key 4 times to remove the "REM " prefix. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press Esc to open the SVED menu, press Down to select Save, and |
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press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I press Esc to open the SVED menu, press Up to select Quit, and |
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press Enter. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I use FDAPM to do a cold boot. |
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C:\>SVARDOS\FDAPM COLDboot |
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I install the unzip program from CD. |
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C:\>pkg install D:\unzip.svp |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I get the disk geometry from FDISK. |
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C:\>FDISK /INFO |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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Note the text "geometry 520/128/63" in the output. |
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I close the QEMU window to power off the virtual machine. |
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# Configure SvarDOS in DOSBox-X |
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I run dosbox-x to create an initial default configuration. |
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$ dosbox-x |
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This opens an initial DOSBox-X window. |
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gopher://tilde.pink/I/~bencollver/log/2025-02-22-install-svardos-in-virtual-mac… |
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I exit DOSBox-X. |
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Z:\>exit |
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I make a backup copy of the DOSBox-X default configuration. |
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$ cp .config/dosbox-x/dosbox-x-2025.02.01{,-orig}.conf |
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I make the SvarDOS specific DOSBox-X configuration. |
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$ cp .config/dosbox-x/dosbox-x-2025.02.01{,-svardos}.conf |
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I edit the SvarDOS specific DOSBox-X configuration. I change the |
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memory size from 16 to 32M to match the qemu virtual machine. |
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DOSBox-X needs the geometry for the raw disk image. Note that FDISK |
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in qemu reported "geometry 520/128/63" and that the sector size is |
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512 bytes. Thus the parameters "-size 512,63,128,520". |
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$ ed .config/dosbox-x/dosbox-x-2025.02.01-svardos.conf |
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104643 |
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/^memsize = 16/s/16/32/ |
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$ |
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a |
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imgmount c /home/ben/Qemu/svardos/svardos.raw -size 512,63,128,520 |
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imgmount d /home/ben/dist/dos/os/svardos/20240915/sv-repo.iso -t iso -fs iso |
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boot c: |
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. |
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w |
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104814 |
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q |
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I create a shell script and run it to start dosbox-x. |
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$ cat >dosbox-svardos.sh <<__EOF__ |
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#!/bin/sh |
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dosbox-x -conf /home/ben/.config/dosbox-x/dosbox-x-2025.02.01-svardos.conf |
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__EOF__ |
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$ chmod a+rx dosbox-svardos.sh |
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$ ./dosbox-svardos.sh |
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That's it! |
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# Configure SvarDOS Real Mode (16-bit) |
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I can optionally configure dosbox-x to emulate a 16-bit 8086 processor. |
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To do so, it is necessary to disable HIMEMX.SYS in CONFIG.SYS because it |
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requires a 32-bit processor. For the same reason it is also |
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necessary to disable the CDROM driver in CONFIG.SYS and AUTOEXEC.BAT. |
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Then i edit the dosbox-x-2025.02.01-svardos.conf file, changing |
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memsize = 1 and cputype = 8086 to specify an 8086 processor with 1M of |
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memory. |
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Below is an article about CD-ROM drives on retro hardware. The CD-ROM |
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drives on 8086 and 80286 PCs were typically single-speed drives using |
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proprietary controllers and drivers. |
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CD-ROM Drives In 286 And 386 PCs |
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# Notes |
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These steps create two virtual machines, one using dosbox-x and the |
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other using qemu. These both use the same disk image. Make sure to |
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power off one before powering on the other. |
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The qemu virtual machine is accelerated using Linux KVM, which runs |
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faster. |
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The dosbox-x virtual machine provides a more accurate BIOS. If your |
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keyboard has a Num Lock key, then you can use Alt Codes to enter |
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special characters in DOSBox-X. |
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Alt code |
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Alt codes do not work in qemu nor VirtualBox because of BIOS bugs. |
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VirtualBox BIOS bug that breaks Alt codes |
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On a tangent, the calvin editor suffers screen corruption because of |
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a bug in VirtualBox's CGA BIOS, INT 10, AH 05h, |
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SELECT ACTIVE DISPLAY PAGE. |
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VirtualBox CGA BIOS bug and calvin workaround |
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I intentionally avoided network configuration in order to |
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"keep it simple." |
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The SvarDOS shell is brutally minimal. The package CD includes 4dos |
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for a more full-featured shell. |
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tags: bencollver,retrocomputing,technical |
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# Tags |
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bencollver |
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retrocomputing |
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technical |
