Difference between user-level and kernel-supported threads?

Question

I\'ve been looking through a few notes based on this topic, and although I have an understanding of threads in general, I\'m not really to sure about the differences bet

Answer 1

Some development environments or languages will add there own threads like feature, that is written to take advantage of some knowledge of the environment, for example a GUI environment could implement some thread functionality which switch between user threads on each event loop.

A game library could have some thread like behaviour for characters. Sometimes the user thread like behaviour can be implemented in a different way, for example I work with cocoa a lot, and it has a timer mechanism which executes your code every x number of seconds, use fraction of a seconds and it like a thread. Ruby has a yield feature which is like cooperative threads. The advantage of user threads is they can switch at more predictable times. With kernel thread every time a thread starts up again, it needs to load any data it was working on, this can take time, with user threads you can switch when you have finished working on some data, so it doesn't need to be reloaded.

I haven't come across user threads that look the same as kernel threads, only thread like mechanisms like the timer, though I have read about them in older text books so I wonder if they were something that was more popular in the past but with the rise of true multithreaded OS's (modern Windows and Mac OS X) and more powerful hardware I wonder if they have gone out of favour.