PCem Migration Guide

PCem users sometimes ask us about migrating their emulated setups to 86Box. While it is true that 86Box started out as a fork of PCem, we have since rewritten many components and made many additions, outgrowing our “fork” status. This post details all the differences between the two emulators that you have to keep in mind when migrating your setups to 86Box.

Performance will be different

One aspect commonly used to compare PCem and 86Box is the emulation performance. There is indeed such a difference, but not everything is as black and white as it seems.

The New Recompiler

PCem v15 introduced a rewritten dynamic recompiler, which was primarily aimed at improving emulation performance in games; however, it also caused minor to severe performance regressions in other applications. One example of a regressed application is the (ironically related to a game) MapEdit level editor for Wolfenstein 3D, which we measured to lose as much as 85% emulation speed with the new recompiler on a relatively sensible Pentium 75 setup.

On x86 host systems, 86Box uses the previous recompiler from PCem versions before v15, with optimizations performed by us, as we have determined that the new one causes too many regressions to be adopted as a sensible default. There is a way for you to try out the new recompiler on 86Box, though: go to our Jenkins, find whatever build number you’re using (here’s 6130, the release build for v4.2.1) and download the New Recompiler (beta) variant that’s right for your host operating system.

On the other hand, ARM host systems always use the new recompiler, as the old one has not received an ARM version. It’s worth noting both recompiler variants for macOS are universal binaries; the old recompiler one automatically switches over to the new recompiler when running on Apple Silicon.

Accuracy is slow

PCem’s emulation of some core system components, such as the Programmable Interval Timer (PIT), takes a few shortcuts to improve performance. These shortcuts are perfectly fine for games, which is what PCem targets; although, they have caused issues with the software preservation side of things, as we found out with Microsoft Word 1.0, the MR BIOS and other old pieces of software.

In addition to taking fewer shortcuts, 86Box also tries to follow the specifications of these components, rather than implement the minimum viable feature set, which is - once again - good enough for games, but not good enough for some other applications. Generally speaking, the more accurate a component’s emulation is made, the more host CPU horsepower it will require. There are certain limits to what’s attainable to emulate (as an example, we don’t do CPU caches, as that is too complex even for other non-PC emulators), but we try to follow what’s possible.

Bring your own manager

PCem has a built-in manager, which allows you to keep and run multiple emulated machine configurations from one place. 86Box does not have such a manager, though one is planned for the future. For now, you can use our 86Box Manager or other manager applications developed by the community, which provide at least basic configuration management.

There is no migration path for configuration files, as the format is too different. You will have to reconfigure your emulated machine on 86Box, but that’s a nice opportunity to double-check your configuration while also checking out our features. More on the differences between PCem and 86Box in the configuration department later.

Machine list

86Box has most of the machines PCem emulates, though we have removed, renamed and/or recategorized some of them for various reasons. The table below (make sure to scroll down) provides a reference for v4.2.

CMOS and Flash

While it’s easier and recommended to just redo the CMOS settings from scratch, you can migrate them (along with Flash ROM data if applicable) from PCem by following these steps:

1. Configure your machine on 86Box, and let it boot into the BIOS once.
2. Exit 86Box. An nvr folder should appear inside the emulated machine’s folder, containing a .nvr file with the machine’s internal name, and also a .bin file with the same name if the machine is equipped with Flash ROM.
3. Copy the <configuration name>.<PCem machine name>.nvr file from PCem’s nvr folder to the 86Box machine’s nvr folder, using the same name as the .nvr file created by 86Box.
4. If the machine is equipped with Flash ROM, copy the flash.bin file from PCem’s roms folder for the machine you’re emulating to the 86Box machine’s nvr folder, using the same name as the .bin file created by 86Box.

PIIX southbridge mismatch

PCem’s implementation of the Intel 430HX, 430VX and 440FX chipsets uses the PIIX southbridge, while real motherboards and 86Box use the PIIX3. Some operating systems, such as Windows NT/2000/XP, will fail to boot after a PIIX to PIIX3 transition (and vice-versa) due to the IDE controller’s new PCI ID.

If you run into this issue, one option is to reinstall the operating system. Another option is to boot the operating system on PCem, uninstall the PIIX IDE driver (on Windows 2000/XP, use Device Manager to replace the 82371FB IDE controller driver with the Standard Dual Channel one), then switch to 86Box.

Settings differences

The 86Box settings interface is designed to be easy to navigate, though you should keep the main differences in relation to PCem in mind:

Machine

• The machine list is split into categories, with the [tag] before a machine’s name denoting its chipset instead of its category. The table above can help you locate PCem’s machines on 86Box.
• The CPU list is split into families instead of manufacturers.
• Only CPUs that are actually compatible with the selected machine will be listed. There are some pitfalls, such as not all Super Socket 7 motherboards supporting the original Pentium without MMX.
• Time synchronization has two options: Local time behaves like PCem and is ideal for running DOS and Windows, while UTC time is ideal for running Linux and other OSes which store time that way.

Display

• Video cards are categorized by their bus (such as ISA or PCI). Any given card might be available on different buses and/or with different manufacturer video BIOS variants.
• The Speed option is not available. 86Box automatically tunes video timings to be accurate to the speed of the card’s bus.

Sound

• There are regular and PnP variants of the Sound Blaster 16 and AWE32 cards. You should stick to the regular variants with manual settings, unless you feel like messing with ISA Plug and Pray Play.
• The MIDI out device option is sound card independent; it’s located right below the sound card selection box. 86Box also supports MIDI input.
• The OPL emulator option is named FM synth driver, with a selection of NukedOPL for accuracy or YMFM for performance.
• The LPT device option is in the Ports (COM & LPT) page, as 86Box supports more devices (such as printers) connected to up to 4 parallel ports.

Drives

• Drives are configured through individual settings pages:
  • Floppy drives in the Floppy & CD-ROM drives page;
  • Hard drives in the Hard disks page;
  • CD-ROM drives in the Floppy & CD-ROM drives page;
  • Iomega Zip drives (86Box adds Zip 250 support) in the Other removable devices page;
  • 86Box adds magneto-optical drives also in the Other removable devices page.
• IDE drives are represented by a channel:device index, instead of a drive index or location like “Primary Master”. See our documentation for more information.
  • IDE channels 2 and 3 correspond to tertiary and quaternary IDE controllers, which can be added through the Storage controllers page. PnP Sound Blaster cards also claim the quaternary channel for their integrated IDE.
• 86Box supports using IDE and SCSI simultaneously. IDE is automatically enabled on machines with it, and up to 4 SCSI controllers can be installed through the Storage controllers page.
• The CD Model and CD Speed options are configurable for each individual drive in the Floppy & CD-ROM drives page, as Type and Speed respectively.

Input

• 86Box can emulate serial and PS/2 mice with three buttons or a scroll wheel. This functionality can be enabled through the Configure button next to the mouse selection box.
• The 4-axis 4-button joystick allows for a more modern control scheme (if supported by the emulated software), which takes advantage of all 4 axes and 4 buttons that the game port provides.

Network

• 86Box supports three networking modes, detailed in our documentation:
  • PCap allows for a bridged connection to a wired Ethernet adapter on the host through pcap libraries (such as Npcap on Windows).
  • SLiRP behaves just like PCem’s private network, with port forwarding available as an added advanced feature.
  • VDE (not available on Windows) can create a virtual network connecting 86Box instances, other emulators and real network interfaces.

User interface

The 86Box user interface should look familiar to PCem users, with two main differences: the menu layout and the status bar. The menu bar had some options moved to the Settings window, and media controls moved to the Media menu. The status bar contains activity indicators, with the same controls as the Media menu also being accessible by clicking the icons. While we don’t have the Machine window, most of what it provides on PCem is accessible through the title bar, menu bar and status bar on 86Box.

Note that the key combination to release mouse capture on 86Box is F8+F12 on Windows hosts, as we’ve found PCem’s Ctrl+End to conflict with some applications. You can also use the middle mouse button to release capture, unless a three-button or wheel mouse is configured.

Media

86Box is quite a bit different in the media department as well. More disk image formats are supported, including our own 86F format for floppy bitstream images. Unlimited hard drives (the controllers are the limit) and up to 4 removable drives of each type (floppy, CD-ROM, Zip, MO) can be installed, with each removable drive getting its own entry on the Media menu and status bar.

Limited host CD-ROM passthrough

86Box currently supports the use of a host CD-ROM drive on Windows hosts only, with more platforms coming soon.

For other platforms, we recommend ripping your discs to .cue + .bin, as that format preserves the sector mode, audio tracks and other information that .iso doesn’t. 86Box also supports .cue images with audio tracks in .wav, .mp3 and other encapsulated or compressed formats.

Zip 250 and MO

86Box supports Iomega Zip 250 disks, which require Zip 250 support to be enabled at a drive level in the Other removable devices settings page. Magneto-optical (MO) is also supported, as another removable medium which provides more storage than Zip disks: up to 1.3 GB per cartridge.

Cassette formats

PCem’s IBM cassette emulation uses the .pzx format, originally designed for ZX Spectrum tapes. 86Box supports the .cas format developed as part of PCE/ibmpc, as well as audio recordings in .wav or .pcm format. The pzx2wav tool in PZX tools can potentially convert .pzx tapes to .wav for 86Box, though we haven’t tested that.

Conclusion

We hope this post helped you understand the differences between PCem and 86Box. We’ve come a long way ever since we forked PCem, but we acknowledge our roots and strive to make things reasonably easy for users coming from PCem. If you have any questions about the migration process or 86Box as a whole, feel free to reach out through Discord or IRC, and we’ll be glad to help.