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Encyclopedia > Physical Address Extension

In computing, Physical Address Extension (PAE) refers to a feature of x86 and x86-64 processors that allows more than 4 gibibytes (GiB) of physical memory to be used in 32-bit systems, given appropriate operating system support. PAE is provided by Intel Pentium Pro and above CPUs (including all later Pentium-series processors except the 400 MHz bus versions of the Pentium M), as well as by some compatible processors such as Athlon and later models from AMD. For the formal concept of computation, see computation. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... The AMD64 or x86-64 is a 64-bit processor architecture invented by AMD. It is a superset of the x86 architecture, which it natively supports. ... A gibibyte is a unit of information or computer storage. ... The term gib may refer to: a castrated male cat or ferret an abbreviation for gibibyte (GiB) or gibibit (Gib) an abbreviation for Gibraltar an abbreviation for Gib Board, itself an abbreviation of Gibraltar Board, all Winston Wallboards[1] tradenames for drywall (plasterboard). ... It has been suggested that this article or section be merged with Primary storage. ... 32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ... An operating system (OS) is a software that manages computer resources and provides programmers with an interface used to access those resources. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... The Pentium Pro is a sixth-generation x86 architecture microprocessor (P6 core) produced by Intel and was originally intended to replace the original Pentium in a full range of applications, but later, was reduced to a more narrow role as a server and high-end desktop chip. ... CPU redirects here. ... Introduced in March 2003, the Pentium M is an x86 architecture microprocessor designed and manufactured by Intel. ... Athlon is the brand name applied to a series of different x86 processors designed and manufactured by AMD. The original Athlon, or Athlon Classic, was the first seventh-generation x86 processor and, in a first, retained the initial performance lead it had over Intels competing processors for a significant... Advanced Micro Devices, Inc. ...


The x86 processor hardware is augmented with additional address lines used to select the additional memory, so physical address size is increased from 32 bits to 36 bits. This increases maximum physical memory size from 4 GiB to 64 GiB. The 32-bit size of virtual address is not changed, so regular application software continues to use instructions with 32-bit addresses and (in a flat memory model) is limited to 4 gibibytes (GiB). The operating system uses page tables to map this 4 GiB address space onto the 64 GiB of total memory, and the map is usually different for each process. In this way the extra memory is useful even though no single regular application can access it all simultaneously. In computer programming, the flat memory model is an approach to organizing memory address space. ... Relationship between pages addressed by virtual addresses and the frames in physical memory, within a simple address space scheme. ... In computing, a process is an instance of a computer program that is being executed. ...


For application software which needs access to more than 4 GiB of memory, some special mechanism may be provided by the operating system in addition to the regular PAE support. On Microsoft Windows this mechanism is called Address Windowing Extensions (AWE), while on Unix-like systems a variety of tricks are used, such as using mmap() to map regions of a file into and out of the address space as needed, none having been blessed as a standard. Windows redirects here. ... Address Windowing Extensions (AWE) is a Microsoft Windows Application Programming Interface that allows a 32-bit software application to access more physical memory than it has virtual address space. ... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ...

Contents

Page table structures

In traditional 32-bit protected mode, x86 processors use a two-level page translation scheme, where the control register CR3 points to a single 4 KiB long page directory, which is divided into 1024 x 4 byte entries that point to 4 KiB long page tables, similarly consisting of 1024 x 4 byte entries pointing to 4 KiB long pages. Protected mode is an operational mode of x86-compatible CPUs of the 80286 series or later. ... A control register is a processor register which changes or controls the behavior of a CPU or other digital device. ... Relationship between pages addressed by virtual addresses and the frames in physical memory, within a simple address space scheme. ... In a context of computer virtual memory, a page, memory page, or virtual page is a fixed-length block of main memory, that is contiguous in both physical memory addressing and virtual memory addressing. ...


Enabling PAE (by setting bit 5, PAE, of the system register CR4) causes major changes to this scheme. By default, the size of each page remains as 4 KiB. Each entry in the page table and page directory is extended to 64 bits (8 bytes) rather than 32 bits to allow for additional address bits; however, the size of tables does not change, so both table and directory now have only 512 entries. Because this allows only half as many entries as the original scheme, an extra level of hierarchy has been added, so CR3 now points to the Page Directory Pointer Table, a short table which contains pointers to 4 page directories.


The entries in the page directory have an additional flag, in bit 7, named PS (for Page Size). If this bit is set to 1, the page directory entry does not point to a page table, but to a single large 2 MB page. The NX bit is another flag in the page directory, in bit 63, to mark pages as "No eXecute". Because the 12 most significant bits of page table entry's 64 bits are either such flags or are available for OS-specific data, a maximum of 52 bits can be potentially utilized in future to address 252 bytes, or 4 pebibytes, of physical memory. The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (or code) or for storage of data, a feature normally only found in Harvard architecture processors. ... A pebibyte is a unit of information or computer storage. ...


The x86 architecture presently uses only 36 bits out of 52 bits possible. On x86-64 processors, PAE is obligatory in native long mode; presently 40 bits are used out of 52 bits possible.[1] Intel Pentium 4 (Northwood version), one example out of a huge number of x86 implementations from Intel, AMD, and others. ... The AMD64 or x86-64 is a 64-bit processor architecture invented by AMD. It is a superset of the x86 architecture, which it natively supports. ... In the x86-64 CPU architecture Long mode, is the mode where an application (or operating system) can access the 64-bit instructions and registers, while 32-bit programs are executed in a compatibility mode. ...


CPU support of PAE mode can be identified via the CPUID flag PAE. The CPUID opcode is an instruction (its name derived from CPU IDentification) for the x86 architecture. ...

Operating system support

FreeBSD

FreeBSD supports PAE in the 4.x series starting with 4.9, in the 5.x series starting with 5.1, and in all 6.x and later releases. The kernel PAE configuration option is required. Loadable kernel modules can only be loaded into a kernel with PAE enabled if the modules were built with PAE enabled; the binary modules in FreeBSD distributions are not built with PAE enabled, and thus cannot be loaded into PAE kernels. Not all drivers support more than 4 GiB of physical memory; those drivers won't work correctly on a system with PAE.[2] FreeBSD is a Unix-like free operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD) branch through the 386BSD and 4. ... In computing, loadable kernel modules, or LKM, are object files that contain code to extend the running kernel, or so-called base kernel, of an operating system. ...


Linux

The Linux kernel includes full PAE support starting with version 2.6.[3] The 2.6 version of the kernel fully supports PAE, enabling access of up to 64 GiB of memory on 32-bit machines. A PAE-enabled Linux-kernel requires that the CPU also support PAE. The Linux kernel is a Unix-like operating system kernel. ...


Solaris

Solaris supports PAE beginning with Solaris version 7. However, third-party drivers used with version 7 and not specifically written to include PAE support may operate erratically or fail outright on a system with PAE.[4] Solaris is a computer operating system developed by Sun Microsystems. ...


Windows

PAE is supported in the following versions of 32-bit Windows:[5][6]

Version Maximum Physical Memory
Windows 2000 Advanced Server 8 GiB
Windows 2000 Datacenter Server 32 GiB
Windows XP Service Pack 2 4 GiB
Windows Server 2003 Enterprise Edition 32 GiB
Windows Server 2003 R2 (or SP1) Enterprise Edition 64 GiB
Windows Server 2003 Datacenter Edition [7] 64 GiB
Windows Server 2003 Standard Edition 4 GiB
Windows Vista SP1 64 GiB[citation needed]
Windows Server 2008 Enterprise or Datacenter Edition 64 GiB
Windows Server 2008 other editions 4 GiB

Windows XP SP2 and later by default on processors with the no-execute (NX) or execute-disable (XD) feature runs in PAE mode in order to allow NX. The NX (or XD) bit resides in bit 63 of the page table entry, and without PAE, page table entries only have 32 bits; therefore PAE mode is required if the NX feature is to be exploited. However, desktop versions of Windows (Windows XP, Windows Vista) limit physical address space to 32 bits for driver compatibility reasons. Windows 2000 Advanced Server is a variant of the Microsoft Windows 2000 Server operating system designed for medium-to-large businesses. ... Windows 2000 (also referred to as Win2K, W2K or Windows NT 5. ... Windows XP is a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... Windows Server 2003 is a server operating system produced by Microsoft. ... Windows Server 2003 is a server operating system produced by Microsoft. ... Windows Server 2003 is a server operating system produced by Microsoft. ... Windows Server 2003 is a server operating system produced by Microsoft. ... Windows Server 2008 is the name of the next server operating system from Microsoft. ... Windows Server 2008 is the name of the next server operating system from Microsoft. ... The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (or code) or for storage of data, a feature normally only found in Harvard architecture processors. ... The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (or code) or for storage of data, a feature normally only found in Harvard architecture processors. ...


See also

In computing, Page Size Extension (PSE) refers to a feature of x86 processors that allows for pages larger than the traditional 4 KiB size. ... The Windows NT operating system familys architecture consists of two layers (user mode and kernel mode), with many different modules within both of these layers. ...

References

  1. ^ Intel 64 and IA-32 Software Developer's Manual - Volume 3A. Intel. Retrieved on 2007-11-16. Page 3.42.
  2. ^ FreeBSD PAE(4) man page (2003-04-08). Retrieved on 2007-11-26.
  3. ^ Wonderful World of Linux 2.6.
  4. ^ Solaris 7 5/99 Release Notes (Intel Platform Edition), Appendix B: Hardware Compatibility List and Device Configuration Guide (Intel Platform Edition) 5/99 (1999). Retrieved on 2007-11-26.
  5. ^ Memory Limits for Windows releases. Microsoft (December 5, 2007). Retrieved on 2007-12-10.
  6. ^ Intel Physical Addressing Extensions (PAE) in Windows 2000. Microsoft (October 26, 2007). Retrieved on 2007-12-29.
  7. ^ Memory Support and Windows Operating Systems (2007). Retrieved on 2008-03-22.

Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 320th day of the year (321st in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... April 8 is the 98th day of the year (99th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 330th day of the year (331st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 330th day of the year (331st in leap years) in the Gregorian calendar. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 344th day of the year (345th in leap years) in the Gregorian calendar. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 363rd day of the year (364th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 81st day of the year (82nd in leap years) in the Gregorian calendar. ...

External links


  Results from FactBites:
 
Physical Address Extension - Wikipedia, the free encyclopedia (294 words)
PAE is provided by Intel Pentium Pro and above CPUs (including all later Pentium-series processors except the 400MHz bus versions on the Pentium M), as well as by some compatible processors such as those from AMD.
The CPUID flag PAE is assigned for the purpose of identifying CPUs with this capability.
The processor hardware is augmented with additional address lines used to select the additional memory, and 36 bit page tables, but regular application software continues to use instructions with 32 bit addresses and a flat memory model limited to 4 gigabytes.
  More results at FactBites »

 
 

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