A community education resource

December 13, 2025

6 min read

Turn off acceleration for an authentic retrocomputing experience

A practical guide to configuring your FreeDOS virtual machine to match the speed and limitations of 1990s computing.

I’ve observed a growing interest in “retrocomputing” over the last several years. Sometimes, people use “retro” technology for work, like how Robert J. Sawyer uses WordStar 7 to write his books; George R.R. Martin does the same with WordStar 4. Others run “retro” computers as a hobby or for fun. For example, I like to use the As-Easy-As spreadsheet for certain tasks because I find this classic DOS spreadsheet does everything that I need a spreadsheet to do.

What computing power was like in the 1990s

When I went to university in 1990, the Intel 80486 CPU was pretty new, having been introduced the previous year. I had an Intel ‘386SX, which was a budget computer for that time. For example, a PC with a ‘386SX CPU at 16 MHz, 2 MB memory, 100 MB hard disk, and VGA graphics might cost over $2,000.

By the time we announced the FreeDOS Project in 1994, the Pentium CPU was still quite new. As an undergraduate student, I didn’t know anyone with a Pentium, but the ‘486 CPU was quite common. A PC with a ‘486DX2 at 66 MHz, 8 MB memory, 730 MB hard disk, CD-ROM drive, and sound card was mid-range and cost around $2,000. I still ran a ‘386SX that had as much extra memory as I could afford, at just 4 MB.

Compare this to today’s computers. A new laptop in 2025 might include a multi-core 3.8 GHz CPU, 32 GB memory, and 512 GB solid state drive. If you buy a new desktop PC, you can find models with 10-core 10-thread CPUs at about 5.3 GHz, 64 GB memory, and 2 TB solid state drive.

Multi-core CPUs don’t really compare to the CPUs from the 1990s, but at a rough approximation we can compare the speeds of a single core CPU. Let’s assume 5.3 GHz is about 5,300 MHz, which is about 330 times faster than the computer I had as a university student, with many thousands of times more memory and storage.

Read more: Why FreeDOS is a modern DOS

Turn off acceleration to experience retrocomputing speed

That’s a lot of text just to say “running a DOS virtual machine at native CPU speeds is a lot more than retro computers.”

If you want to experience what “retrocomputing” is like, I encourage you to turn off acceleration in your virtual machine. For example, if you use QEMU to run FreeDOS, avoid the -enable-kvm option, which forces QEMU to run CPU instructions through software. This will effectively slow down the emulated CPU; it won’t run as slowly as 16 MHz, but it will approximate the feel of classic computing.

Also, use memory and storage values that approximate computers from the early 1990s, such as 4 MB memory and 100 MB hard disk. For a “mid 1990s” experience, you might use as much as 8 MB memory and 500 MB hard disk. I use similar values on my FreeDOS virtual machine.

Let’s try it! Download the FreeDOS 1.4 distribution from our website. Or if you want to experiment with the latest patches, download the monthly test release from our Files Archive at Ibiblio. I’ll demonstrate with the monthly test release, currently at “T2512” which means “Test, 2025, December.” The LiveCD version is FDT2512-LiveCD.zip, which extracts to a CD image called T2512LIVE.iso.

Installing FreeDOS on QEMU

Set up a new virtual disk using the qemu-img command. I use the QCOW2 disk format, which is the standard disk image format for QEMU. Specify a 100 MB hard disk, which is typical of early 1990s PCs:

$ qemu-img create -f qcow2 disk.qcow2 100M
Formatting 'disk.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=104857600 lazy_refcounts=off refcount_bits=16

Then, start a QEMU virtual machine with the virtual disk as the hard disk, and the LiveCD image as the CD-ROM drive. QEMU supports a ton of command line options to configure all parts of the virtual machine, but we can get by with just a few common options to set the PC type (-machine), disks (-hda and -cdrom), and memory (-m). The -machine help option lists all available PC types that QEMU supports.

$ qemu-system-i386 -machine help | tail
pc-q35-5.0           Standard PC (Q35 + ICH9, 2009) (deprecated)
pc-q35-4.2           Standard PC (Q35 + ICH9, 2009) (deprecated)
q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-10.1)
pc-q35-10.1          Standard PC (Q35 + ICH9, 2009)
pc-q35-10.0          Standard PC (Q35 + ICH9, 2009)
isapc                ISA-only PC
none                 empty machine
x-remote             Experimental remote machine
xenpv                Xen Para-virtualized PC
xenpvh               Xen PVH x86 machine

I’ll use the isapc machine type to create an ISA-only virtual PC, with just 4 MB memory. ISA is the original Industry Standard Architecture, the 16-bit bus from early PC computers like the PC/AT. I’ve left other configuration values to the QEMU defaults, which include Cirrus CLGD 5446 PCI VGA card (you can force this value with -vga cirrus), PS/2 mouse and keyboard. Although to set up a Creative SoundBlaster 16 sound card with Adlib (OPL2) Yamaha YM3812 compatible chip requires using other command line options to connect the virtual sound to my Linux audio system; I’ve skipped sound in this demonstration.

$ qemu-system-i386 -machine isapc -m 4 -hda disk.qcow2 -cdrom T2512LIVE.iso -boot order=d

Select “Install to harddisk” at the boot menu.

Read more: Explore the five steps of the FreeDOS boot sequence

Walking through the installation

The FreeDOS installer should walk you through the steps to set your preferred language and partition the hard disk. You’ll need to reboot afterwards; like any DOS, FreeDOS reads the partition table exactly once, at boot-up. That means FreeDOS needs to reboot after you modify the partition table, so it can see the new partitions.

As you go through the installation steps, you may notice that each step has a significant delay. For example, formatting the C: drive and installing the packages takes quite a bit of time. This is because QEMU is running without Linux KVM support (without -enable-kvm) so all CPU instructions are emulated. Without the KVM acceleration, the virtual machine is running much slower. While not as slow as a 16 MHz PC from the 1990s, this approximates the slower speed of classic computing.

Installing FreeDOS as a “plain DOS” system, with just the minimum packages required for a classic “DOS” system, takes about ten minutes. By comparison, installing FreeDOS on a new virtual machine that uses KVM takes just moments.

The classic computing experience

It’s tempting to run virtual machines with as much memory and disk as you can spare, and with all acceleration and optimizations enabled. But if you want to experience what a tiny operating system like DOS was like, try using a virtual machine that approximates the hardware of the era. I rarely run FreeDOS with more than 8 MB or 16 MB memory and 500 MB virtual disk, even though FreeDOS can address more memory and disk than that. Running FreeDOS with a limited virtual machine is really the best way to experience “retrocomputing” today.

More from We Love Open Source

• Building As-Easy-As: A spreadsheet born out of scientific need
• Explore the five steps of the FreeDOS boot sequence
• How to write your first FreeDOS program
• How I run virtual machines with QEMU
• Why FreeDOS is a modern DOS

About the Author

Jim Hall is an open source software advocate and developer, best known for usability testing in GNOME and as the founder + project coordinator of FreeDOS. At work, Jim is CEO of Hallmentum, an IT executive consulting company that provides hands-on IT Leadership training, workshops, and coaching.

Read Jim’s Full Bio

The opinions expressed on this website are those of each author, not of the author’s employer or All Things Open/We Love Open Source.

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