NEED HELP WITH DEFYING SOME MAJOR HEADINGS IN OPERATINGS SYSTEMS?

Question

WHAT IS ADDRESSED VIRTUAL MEMORY?

WHAT IS OVERLAY STRUCTURES?

WHAT IS IMPLEMENTING VIRTUAL MEMORY?

Answer 1

First:  TURN OFF THE CAPS LOCK KEY.

Now:  "virtual" is a term from optics.  It refers to an image that only appears to be there.  In this case, virtual memory is as opposed to physical memory.  Physical memory is, basically, the RAM in your system.  Virtual memory is space on the hard drive that is allocated and set up to appear to the system as RAM.  Many times, virtual memory is just a place to shuffle files that are technically in RAM but that the machine isn't using right now.  Addressed virtual memory would be space on the hard drive that may be accessed exactly the same way RAM is - by address.  (Note:  virtual memory is very much slower than physical RAM).

Implementing means to set it up.  So, when you implement virtual memory, you're telling your system to use some hard drive space as a substitute for RAM.

Overlay structures have a couple of definitions.  The only one with which I'm familiar is in programming.  Sometimes, you'll write a program that has modules that you don't need all the time.  You can implement these as overlays.  Some section of the memory in which your program is running is set aside as overlay space.  When the program needs one of those modules, it copies it into that space.  If it needs a different one, it overlays the new one on top of the old one, replacing it.