A PC cannot currently contain 4 pebibytes of memory ( due to the physical size of the memory chips ), but AMD envisioned large servers, shared memory clusters, and other uses of physical address space that might approach this in the foreseeable future.
12.
The page table structure used by x86-64 CPUs when operating in 64-bit mode further extends the page table hierarchy to four levels, extending the virtual address space, and uses additional physical address bits at all levels of the page table, extending the physical address space.
13.
Memory management and multitasking or to increase the memory capacity beyond the limits imposed by the processor's physical address space, but the key feature of a flat memory model is that the entire memory space is linear, sequential and contiguous from address zero to MaxBytes " 1.
14.
However, " client " versions of 32-bit Windows ( Windows XP SP2 and later, Windows Vista, Windows 7 ) limit physical address space to the first 4 GB for driver compatibility via the licensing limitation mechanism, even though these versions do run in PAE mode if NX support is enabled.
15.
RPCs are a form of inter-process communication ( IPC ), in that different processes have different address spaces : if on the same host machine, they have distinct virtual address spaces, even though the physical address space is the same; while if they are on different hosts, the physical address space is different.
16.
RPCs are a form of inter-process communication ( IPC ), in that different processes have different address spaces : if on the same host machine, they have distinct virtual address spaces, even though the physical address space is the same; while if they are on different hosts, the physical address space is different.
17.
This means that for other memory areas, the data has to be transferred first by DMA from the I / O device to an intermediate buffer in the first 16 MiB of the physical address space, and then moved to the final memory by the CPU; or, in the other direction, it must be transferred from the initial memory to the intermediate buffer by the CPU before being transferred by DMA from that buffer to the I / O device.
18.
In current 32-bit x86 computers, this commonly ( although does not have to, as this is a configurable option ) takes the form of a 3GB / 1GB split of the 4GB address space, so kernel virtual addresses start at 0xC0000000 and go to 0xFFFFFFFF . The lower 896 MB, from 0xC0000000 to 0xF7FFFFFF, is directly mapped to the kernel physical address space, and the remaining 128 MB, from 0xF8000000 to 0xFFFFFFFF, is used on demand by the kernel to be mapped to high memory.
19.
:: The reasons kernel-space programs can still hit page faults is the entire physical address space isn't entirely filled with mapped RAM, ROM, Flash etc chips-only certain areas are, for which the MMU has a ( generally fixed, sometimes hardwired ) mapping to actual chip selects-so ( depending on the architecture ) if kernel space code tries to access physical memory that has no valid CS mapping the MMU will barf at it .-- Talk 13 : 23, 14 March 2008 ( UTC)
