"Actually", his sentence begins with the word "Initially".

> Initially built on top of DOS, Microsoft painstakingly added version after version, always striving for backward compatibility while, at the same time, adding new features.

It was "initially" built on DOS. And over time, Microsoft painstaking strove for backward compatibility, not giving it up even for a major architecture change. NT offered a DOS VM (VDM) / Windows VM (WoW)[1], and Windows 7 offers an XP VM [2].

[1] http://kb.iu.edu/data/acxn.html [2] http://www.microsoft.com/windows/virtual-pc/download.aspx

His sentence does seem misleading to me: it reads like he thinks Windows at the core OS level (the scheduling/memory-management/drivers/etc. stuff he mentions in the intro) is still incrementally built on top of the old DOS-lineage code, as opposed to recognizing that it underwent a complete rewrite. If he's just arguing that the API evolution has been constrained by the need for backwards compatibility, that's true, but doesn't make much sense to his point in this context.

Yes and "initially" Unix could only run one process at a time. But modern Unix is far in advance, and modern Windows is far in advance of DOS.

What are you talking about? Even Multics was multitasking. Heck, that's already in the name.

Unix has no code in common with Multics.

In the first Unix, starting a process from the shell did exec, not fork. When the "child" process exited, the kernel would restart the shell. All the process control stuff came when Unix was rewritten in C from the original assembly.

I know they have no code in common. I'm talking about the fact that both were multitasking from the beginning. You're talking about specific early shell behavior. Nothing to do with capabilities of kernel which provided multitasking for two terminals at once.

Processes (independently executing entities) existed very early in PDP-7 Unix. There were in fact precisely two of them, one for each of the two terminals attached to the machine.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.156...