MS-DOS EMULATION

Manufacturer: Microsoft  / Release Date: 1981

MS-DOS was the primary operating system for PCs in the 1980s and the first half of the 1990s, and just about all games released during this time require it to run. While even modern versions of Windows retain a "command prompt" that functions similarly to DOS, the full-featured version of it stopped being included with Windows around 2000. Microsoft has released the early versions of it to the public and there are free equivalents such as FreeDOS, but to play games most people simply use the excellent DOSBox which has been around for almost two decades now. 

MS-DOS Emulation Guide For PC 

Recommended Emulators: DOSBox for most games; ScummVM for select games that it supports  (both available for Windows, Linux and MacOS). PCEm for games that are very finicky about emulation of specific CPUs.

Minimum System Requirements: Basic Emulation (about as low as it goes, pretty much anything will run DOS games)

DOSBox

DOSBox is a matter of simply downloading it and installing it. No extra files to go find, it's ready to go once installed. For those who have not used DOS before it is a little complicated at first, however. 

DOSBox will install like a typical program. When you run it, you'll be dumped to a simulated DOS environment with a command prompt. What you'll want to do is create a directory to hold all of your various DOS games each in their own folders. Preferably keep the folder names to short one-word titles to make things easier. 

Don't worry about learning how to navigate DOS, you only really have to know a small handful of commands to run most games:

* mount c: (main directory that holds your DOS game folders)

In other words, if your DOS game directory is in c:\games\dos in Windows, the command you would enter is "mount c: c:\games\dos". This creates a virtual c: drive within DOSBox that contains the contents of your Windows DOS games directory. 

Once mounted, type "c:" to change to the new virtual drive.

* dir 

Shows all the game directories / files in the current directory. type "dir/p" in directories with lots of files to slowly scroll through the filenames.  type "dir *.exe", "dir *.com" or "dir *.bat" to find the types of files that start games up. 

* cd (directory name)

Change to the game directory. type "c:" to go back to the root directory.

* You simply type the name of the executable file (without the extension) to run the game. It's usually either "start", "run" or some sort of shortened version of the game's name to start it. 

* Once a game is running, press Alt+E to switch to fullscreen. 

* Most games will work just fine with these basics. Old games are iffy on joystick support, but if they have it DOSBox should auto-detect modern pads like the XBox and let you use them. The occasional game will require you to futz a little with timing settings, you can Google for settings for each individual game if something runs too fast, too slow or freezes / crashes. 

* Games that require you to mount CD images also require special startup commands, covered here 

If all of this sounds too complicated, you can try out a frontend that simplifies things to a more Windows-like clicky interface

ScummVM

ScummVM supports far fewer games than DOSBox (and has a particular focus on adventure games), but has some added features that make it worth using for games that it supports. It is much easier to use, has some added bonus stuff and can even run games for other types of computers (like the FM TOWNS). It's pretty self-explanatory, just download it and go. 

PCEm

PCEm is the choice if you want the most accurate possible emulation (something that's very helpful for DOS games that are fussy about being run at particular CPU clock speeds, which DOSBox only roughly and somewhat inaccurately emulates with its "cycles" system). It has the upshot of also being useful for running older versions of Windows (ie to run games that require Win 3.1 or Win 95/98). 

The downsides? Much higher hardware requirements than the other options (you'll probably need a gaming-quality PC), and much more complicated to set up and run software with. 

Peripherals:

Gamepad  -  highly recommended for action games

Flight stick  - for flight sims, Wing Commander games and such

Graph paper  -  Old DOS RPGs are all about that manual mapping

USB floppy drive  - If you want to recreate the authentic experience of swapping 7 disks and waiting 10 minutes for your saved game to load ... or you just have some old disks to copy off of

Links for DOS Gamers

MetzoMagic  (Reviews & technical emulation articles, loads of nostalgia)

Vogons  (DOS-themed site with lots of old PC hardware and software emulation information)

Running Windows 3.1 With DOSBox

Unlike later versions of Windows, Win 3.1 was just a piece of software that you manually ran at your leisure after your computer booted to the usual DOS prompt. Which means ... we can run it in DOSBox! Actually getting games running takes some extra steps, but is quite doable. There's a great guide to it at Vogons. 

There is also an easier way to play some 1000 Win 3.1-exclusive games right in your web browser: check out this relevant section of the Internet Archive. 

Wanna install DOS and Win 3.1 on an iPad? Well, you can do that too apparently.