Xcode Instruments. What is the meaing of Virtual Memory? iPhone OS has no VM?

I've been staring at the Memory Monitor in Instruments and I am scratching my had. Why is it displaying virtual memory? iPhone OS has no virtual memory. What does it mean?

My concern is t开发者_运维百科hat I am getting memory warnings for my iPad app but the apps real memory never exceeds 70MB and the virtual memory never exceeds 180MB?

Could someone please enlighten me?

Cheers,

Doug

(Virtual memory does not (just) mean using the hard disk as memory, but a technique that transforms addresses used in application to a real physical memory location.)

From New Feature in iPhone OS 3.1 with Snow Leopard: VM Tracker:

The VM Tracker instrument is designed to report on a target process' virtual memory space, showing all of the regions mapped into the address space along with information and statistics relevant to the mapping type. For example, a region that is a memory-mapped file via an mmap call will show as a "mapped file" region and display the path for the file it references. Instruments shows size statistics for each region as well: virtual, resident, and dirty.