Q failure to wake and resetting the PMU

Question

Every once in a while (roughly once per week, on average) my MacBook will not wake from sleep, no matter what I try. The only recourse is to turn it off and back on again, which is a huge inconvenience.
This seems to be a very common problem, and I've found many posts on it online. A frequently offered piece of advice is to reset the PMU, as described here
http://docs.info.apple.com/article.html?artnum=303319
However, this article states that resetting the PMU should be done only as a last resort, after one has tried to do things such as pressing the power button for 10 seconds.
Since my machine does respond pressing the power button 10 seconds, the above suggests that I should NOT attempt to reset the PMU.
My questions are: why is resetting the PMU regarded as something to do as a last resort, and would it be of any help for me to try it (considering that my machine does respond to pressing the power button for 10 seconds)?
Thanks!
tlm1905

Answer 1

Resetting the PMU does not affect the hard drive. Here's how:
http://docs.info.apple.com/article.html?artnum=14449
RAM chip contents vary depending on what you have open on your computer, and resets itself everytime you reboot the computer. The hard drive has its own swap file for RAM as well which varies with what is open, but it does not affect the contents of your data or applications. There are two kinds of RAM which confuses many computer novices:
The hard drive itself which is a spinning platter inside a rectangular case that looks much like an old LP player.
The RAM chips which are on a computer circuit board.
Only the hard drive stores actual data that you use and applications.
The RAM chips act as a buffer for multitasking applications, and the swap file on the hard drive act as an additional buffer.