virtual-memory

I am often confused with the concept of virtualization in operating systems. Considering RAM as the physical memory, why do we need the virtual memory for executing a process? Where does this virtual memory stand when the process (program) from the external hard drive is brought to the main memory (physical memory) for the execution. Who takes care of the virtual memory and what is the size of the virtual memory? Suppose if the size of the RAM is 4GB (i.e. 2^32-1 address spaces) what is the size of the virtual memory? Virtual memory is, among other things, an abstraction to give the programmer

In a book I read the following: 32-bit processors have 2^32 possible addresses, while current 64-bit processors have a 48-bit address space My expectation was that if it's a 64-bit processor, the address space should also be 2^64. So I was wondering what is the reason for this limitation? Because that's all that's needed. 48 bits give you an address space of 256 terabyte. That's a lot. You're not going to see a system which needs more than that any time soon. So CPU manufacturers took a shortcut. They use an instruction set which allows a full 64-bit address space, but current CPUs just only

What are the reasons a malloc() would fail, especially in 64 bit? My specific problem is trying to malloc a huge 10GB chunk of RAM on a 64 bit system. The machine has 12GB of RAM, and 32 GB of swap. Yes, the malloc is extreme, but why would it be a problem? This is in Windows XP64 with both Intel and MSFT compilers. The malloc sometimes succeeds, sometimes doesn't, about 50%. 8GB mallocs always work, 20GB mallocs always fail. If a malloc fails, repeated requests won't work, unless I quit the process and start a fresh process again (which will then have the 50% shot at success). No other big