Resurrected Entertainment

Archive for the 'Retro' category

MS-DOS is Cross Platform

May 2, 2023

Cross platform programming is a labour of love. It’s also requires a large time investment to get it right, so you should only do it if you really need to. There are many technologies available to help you on that journey; if you are building an application, then you’ll probably take a different path than if you are programming a game, and it’s the latter scenario that I would like to dig into a bit.

Let’s suppose you want to program a small game that doesn’t require easy access to 3D hardware, fancy input devices, or the Internet. Okay, I probably lost most of you right there, but for those that powered through, let’s continue.

I have a lot of nostalgia around the MS-DOS platform. It was not the first platform on which I began programming, that honour belongs to the Atari 800 XL, but it was still a lot of fun to use and explore. Compared to desktops nowadays, it is obscenely limited, but back in the 80s/90s it felt just right. MS-DOS is a 16-bit operating system and native access to memory beyond 65,536 bytes was the stuff of fantasy. Luckily, that limitation was relatively short lived, and you could access heaps of memory (get it?) by leveraging DOS extenders, such as DOS/4G, DOS/32, or CWSDPMI. If they packed the right set of low level features, these run-time utilities were all enabled by your friendly 386 CPU, and allowed the adventurous programmer to enter protected mode and access much more memory. For completeness, 286 CPUs did support protected mode but they lacked important features, so it was never heavily adopted

Once you jumped the hurdle of available memory, there were other lions that hapless bell bottomed programmers needed to tame. They also had cope with performance differences between CPUs (with or without co-processors), sound hardware, hard-drive storage (or lack thereof), video hardware, and input device support. Phew. As a result of all this variability, many MS-DOS compatible games were faced with cross-platform challenges on the same, err, platform.

Unfairly, this wasn’t an issue when faced with game console development. The company promoting a console could always choose to add new hardware, such as steering wheel for racing games or new ways of visualizing content, or even additional performance, but it couldn’t do so in a way that would break existing applications. Note that this isn’t necessarily true for consoles built in the last 20 years. For these machines, the hardware remains compatible, but the software could change a lot, which would require game developers to retool their application from time to time. We won’t talk about that messy bit of reality right now.

During the 8- and 16-bit era, game consoles provided a stable environment to build games. This stability lead to lower production costs and faster delivery times. In reality, many companies chose to release their games on several different platforms which dirties the water a bit. We will sweep these software development complexities under the rug as well since the porting strategies used did not impact their code-base in the same way as cross-platform development would affect their projects today. For example, many companies had distinct implementations for each platform, and code reuse was the exception rather than the rule.

Ironically, given the eccentric nature of MS-DOS in its heyday which lead to all sorts of programming headaches, it’s surprising that using a current incarnation of MS-DOS today produces such a stable environment. All you need is the right level of abstraction. Sure, you could always choose to support MS-DOS and all of its gory hardware configurations, or you could target one configuration and enjoy all of that sweet compatibility. What is this magical solution? Well, this paradise of splendour can be had by leveraging emulators like DOSBox. Yes, the solution to the fragmented environment that is an MS-DOS gaming machine is the venerable DOSBox. It is an excellent way to release your game on dozens of platforms without writing a lick of extra code. Want to run your game on Linux? No problem. What about Mac? No problem. Any console with an open development environment and suitable performance characteristics can (and likely does) support DOSBox, or one the excellent downstream projects like DOSBox-X. This means, your game can run on all of those supported platforms too. Go on, grab some MS-DOS development tools and get coding!

Custom Pac-Man Themed Arcade

January 17, 2016

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