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In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension, [1] is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro , and later by AMD in the Athlon processor. [ 2 ]
The 32-bit PAE desktop kernel (linux-image-generic-pae) in Ubuntu 9.10 and later, also provides the PAE mode needed for hardware with the NX CPU feature. For systems that lack NX hardware, the 32-bit kernels now provide an approximation of the NX CPU feature via software emulation that can help block many exploits an attacker might run from ...
Many 32-bit computers have 32 physical address bits and are thus limited to 4 GiB (2 32 words) of memory. [3] [4] x86 processors prior to the Pentium Pro have 32 or fewer physical address bits; however, most x86 processors since the Pentium Pro, which was first sold in 1995, have the Physical Address Extension (PAE) mechanism, [5]: 445 which allows addressing up to 64 GiB (2 36 words) of memory.
The NX bit (no-execute) is a technology used in CPUs to segregate areas of a virtual address space to store either data or processor instructions. An operating system with support for the NX bit may mark certain areas of an address space as non-executable. The processor will then refuse to execute any code residing in these areas of the address ...
An example is a 32-bit x86 processor with 4 GB and without Physical Address Extension (PAE). In this case, the processor is able to address all the RAM installed and no more. However, even in this case, paging can be used to support more virtual memory than physical memory. For instance, many programs may be running concurrently.
Typically, kernel space programs run in kernel mode, also called supervisor mode; normal applications in user space run in user mode. Some operating systems are single address space operating systems—they have a single address space for all user-mode code. (The kernel-mode code may be in the same address space, or it may be in a second ...
SunOS 4 includes what is most likely the earliest implementation of tmpfs; it first appeared in SunOS 4.0 in late 1987, together with new orthogonal address space management that allowed any object to be memory mapped. [1] [2] The Solaris /tmp directory was made a tmpfs file system by default starting with Solaris 2.1, [3] released in December ...
Each page table entry (PTE) holds the mapping between a virtual address of a page and the address of a physical frame. There is also auxiliary information about the page such as a present bit, a dirty or modified bit, address space or process ID information, amongst others.