[criddell]

At the same time, his programs do things like modify themselves. CPUs and operating systems haven't let you do stuff like that for a while now, at least not without disabling system protections.

Also, the underlying hardware he's describing isn't universal. Look at the assembly language for a vector machine (like a Cray). It's nothing like MIX.

[dhosek]

If you look at the link, Knuth does talk about how self-modification is an obsolete practice and something he has been removing.