Per Jessen wrote:
James Knott wrote:
While I don't have the exact details of PAE, in general memory mapping works by mapping physical memory outside of the normal addressing range, to an address within that range. This means that only a portion of that physical address range can be visible at a given time. An application has to be able to tell the operating system what portion of the physical memory it wants and also where in address space it wants it to be located.
Err, no. In Linux and many other OSes with virtual memory, no application needs to "tell the operating system what portion of the physical memory it wants" nor "where in address space it wants it to be located.". It only needs to say HOW MUCH it wants, and the virtual memory manager takes care of the rest.
Forgot to mention in the other note. We're not talking about virtual memory here, which is an entirely different thing. Virtual memory is the process for making disk space appear as actual memory. This is transparent to the app. Memory mapping is a technique for allowing an app to access more memory space than it's normally able to. For example, in an earlier note, I mentioned the Zilog Z80 CPU, which, with 16 bit addressing, could only access 64 KB of memory. The memory mapper allowed it to access considerably more, but still only a total of 64 K at a time. With PAE, the same situation occurs. On 32 bit computes, a process can normally access only a 4 GB range. PAE allows access to more than that range, provided that the total amount of available space is no more than 4 GB. In order to use that greater range, an app has to use the PAE API to instruct the OS to make that memory beyond 4 GB available. If the app doesn't use PAE, it can't go beyond the basis 4 GB. Memory mapping and PAE work by mapping physical memory into a "window" within the normal address range. -- Check the headers for your unsubscription address For additional commands send e-mail to suse-linux-e-help@suse.com Also check the archives at http://lists.suse.com Please read the FAQs: suse-linux-e-faq@suse.com