Different CPU architectures mean that running DOS on the Raspberry Pi is not easy, but it’s not that troublesome.

FreeDOS may be familiar to everyone. It is a complete, free and well-compatible operating system for DOS. It can run some older DOS games or commercial software, and can also develop embedded applications. Any program that can run on MS-DOS can run on FreeDOS.

As the initiator and project coordinator of FreeDOS, many users will ask me questions as an insider. And the question I get asked most often is: "Can FreeDOS run on a Raspberry Pi?"

This question is not surprising. After all, Linux can run very well on the Raspberry Pi, and FreeDOS is an older operating system that takes up less resources than Linux. So why can’t FreeDOS run on the Raspberry Pi?

Simply put. Due to the CPU architecture, FreeDOS cannot run independently on the Raspberry Pi. Like other DOS-like systems, FreeDOS requires an Intel x86 architecture CPU and BIOS to provide basic runtime services. The Raspberry Pi runs on an ARM architecture CPU, which is not binary compatible with Intel CPUs and does not have a BIOS. Therefore, Raspberry Pi does not support FreeDOS at the hardware level.

However, you can still run FreeDOS on the Raspberry Pi through a PC emulator. Although this may be slightly insufficient, it is still a method to run FreeDOS on the Raspberry Pi.

Some people may ask: "Why not use DOSBox?" DOSBox is an open source cross-platform x86 emulator that can also be used on Linux. It can provide a DOS-like running environment for application software, especially game software, so If you just want to play DOS games, DOSBox is a good choice. But in the eyes of the public, DOSBox is designed specifically for DOS games, and when it comes to running some other DOS application software, DOSBox only performs mediocrely.

For most people, this is just a matter of personal preference. I like to use FreeDOS to run DOS games and other programs. A complete DOS system allows me to experience better flexibility and controllability than DOSBox. I only use DOSBox for gaming, and otherwise choose full FreeDOS.

QEMU (Quick EMUlator) is an open source virtual machine software that can run DOS systems on Linux systems. Many popular Linux systems come with QEMU. QEMU also runs on my Raspbian system on the Raspberry Pi. Below are some screenshots of me using QEMU on the Raspbian GNU/Linux 9 (Stretch) system on the Raspberry Pi.

I used QEMU last year when I wrote an article about how to run DOS programs in Linux systems. The steps to use QEMU to install and run FreeDOS on the Raspberry Pi are basically the same as on other GNOME-based systems. There is no big difference.

In QEMU you need to build a virtual machine by adding various components. First specify a virtual disk image to install and run DOS, and create a virtual disk image through the qemu-img command. FreeDOS does not require much space, so I only created a 200MB virtual disk:

qemu-img create freedos.img 200M

Unlike PC emulators such as VMware or VirtualBox, using QEMU requires adding various components to build a virtual machine. Although it is a bit troublesome, it is not difficult. I used the following parameters to install FreeDOS using QEMU on the Raspberry Pi:

qemu-system-i386 -m 16 -k en-us -rtc base=localtime -soundhw sb16,adlib -device cirrus-vga -hda freedos.img -cdrom FD12CD.iso -boot order=d

You can find a complete introduction to these commands in my other articles. Simply put, the above command specifies an Intel i386-compatible virtual machine and allocates 16MB of memory, an English input keyboard, a real-time clock based on system time, a sound card, a music card, and a VGA card. The file freedos.img is designated as the first hard drive (C:), and the FD12CD.iso image is designated as the CD-ROM (D:) drive. QEMU is configured to boot from the CD-ROM in D:.

You only need to follow the prompts to install FreeDOS 1.2 easily. But since microSD cards are slow when faced with heavy I/O, installing the operating system takes a long time.

你的運(yùn)行情況取決于使用哪一種 microSD 卡。我用的是 SanDisk Ultra 64GB microSDXC UHS-I U1A1 ，其中 U1 這種型號(hào)專用于支持 1080p 的視頻錄制（例如 GoPro），它的最低串行寫速度能夠達(dá)到 10MB/s。相比之下，V60 型號(hào)專用于 4K 視頻錄制，最低連續(xù)寫入速度能達(dá)到 60MB/s。如果你的樹莓派使用的是 V60 的 microSD 卡甚至是 V30（也能達(dá)到 30MB/s），你就能明顯看到它的 I/O 性能會(huì)比我的好。

FreeDOS 安裝好之后，你可以直接從 C: 進(jìn)行啟動(dòng)。只需要按照下面的命令用 -boot order=c 來指定 QEMU 的啟動(dòng)順序即可：

?qemu-system-i386 -m 16 -k en-us -rtc base=localtime -soundhw sb16,adlib -device cirrus-vga -hda freedos.img -cdrom FD12CD.iso -boot order=c?

只要樹莓派的 QEMU 上安裝了 FreeDOS，就不會(huì)出現(xiàn)明顯的性能問題。例如游戲通常在每一關(guān)開始的時(shí)候會(huì)加載地圖、怪物、聲音等一系列的數(shù)據(jù)，盡管這些內(nèi)容需要加載一段時(shí)間，但在正常玩的時(shí)候并沒有出現(xiàn)性能不足的現(xiàn)象。

FreeDOS 1.2 自帶了很多游戲以及其它應(yīng)用軟件，可以使用 FDIMPLES 包管理程序來安裝它們。FreeDOS 1.2 里面我最喜歡的是一款叫 WING 的太空射擊游戲，讓人想起經(jīng)典的街機(jī)游戲 Galaga（WING 就是 Wing Is Not Galaga 的遞歸縮寫詞）。

As-Easy-As 是我最喜歡的一個(gè) DOS 應(yīng)用程序，作為 20 世紀(jì)八九十年代流行的電子表格程序，它和當(dāng)時(shí)的 Lotus 1-2-3 以及現(xiàn)在的 Microsoft Excel、LibreOffice Calc 一樣具有強(qiáng)大的威力。As-Easy-As 和 Lotus 1-2-3 都將數(shù)據(jù)保存為 WKS 文件，現(xiàn)在新版本的 Microsoft Excel 已經(jīng)無法讀取這種文件了，而 LibreOffice Calc 視兼容性而定有可能支持。鑒于 As-Easy-As 的初始版本是一個(gè)共享軟件，TRIUS 仍然為 As-Easy-As 5.7 免費(fèi)提供激活碼。

我也非常喜歡 GNU Emacs 編輯器，F(xiàn)reeDOS 也自帶了一個(gè)叫 Freemacs 的類 Emacs 的文本編輯器。它比 FreeDOS 默認(rèn)的 FreeDOS Edit 編輯器更強(qiáng)大，也能帶來 GNU Emacs 的體驗(yàn)。如果你也需要，可以在 FreeDOS 1.2 中通過FDIMPLES包管理程序來安裝。

即使樹莓派在硬件上不支持 DOS，但是在模擬器的幫助下，DOS 還是能夠在樹莓派上運(yùn)行。得益于 QEMU PC 模擬器，一些經(jīng)典的 DOS 游戲和 DOS 應(yīng)用程序能夠運(yùn)行在樹莓派上。在執(zhí)行磁盤 I/O ，尤其是大量密集操作（例如寫入大量數(shù)據(jù)）的時(shí)候，性能可能會(huì)受到輕微的影響。當(dāng)你使用 QEMU 并且在虛擬機(jī)里安裝好 FreeDOS 之后，你就可以盡情享受經(jīng)典的 DOS 程序了。

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