Several times in the last couple of decades, Microsoft has released source code for the original MS-DOS operating system that kicked off its decades-long dominance of consumer PCs. This week, the company has reached further back than ever, releasing “the earliest DOS source code discovered to date” along with other documentation and notes from its developer. Today’s source release is so old that it predates the MS-DOS branding, and it includes “sources to the 86-DOS 1.00 kernel, several developm...