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What Is a Physical Address Extension?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 29 September 2016
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    Conjecture Corporation
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Physical address extension (PAE) is a method of converting a computer’s memory, including the random access memory (RAM) and all other virtual memory, into general system memory. This can only be done on systems that are 32-bit, use x86 processors and have more than 4 gigabytes (4 GB) of memory. By doing this, the computer will have memory for applications and caching, and it will not section off the memory as it usually would. The physical address extension memory management was created by Intel® in 1995 and has been included in many different operating systems (OS).

In 32-bit systems, when the overall memory is or exceeds 4 GB, all the memory cannot be used and accessed. By running the computer in physical address extension mode, the computer is able to use all the memory and converts it into general system memory. This memory management was created in 1995 by Intel® for its Pentium Pro® central processing unit (CPU) and has been used in many models since its creation. When this mode is enabled, a level is added to the memory hierarchy, allowing for more memory usage without the computer burning out or crashing.

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Physical address extension can only be used in 32-bit systems when the memory is 4 GB or higher. In other systems above 32 bit, PAE mode may be automatic, or other memory management schemas may be used in lieu of PAE. This is made to utilize memory more than 4 GB, so systems with less memory will not be able to access this feature, because nothing would change if it were enabled.

The total amount of memory that can be used depends on the OS. The minimum is 4 GB, but more advanced systems can access more than 100 GB of memory. Server computers typically use this, because such a high amount of memory is necessary to perform daily tasks. In home computers, the minimum amount will usually be sufficient for most tasks.

When physical address extension is enabled, all the memory will convert into system memory, so it can be used for applications. This means programs are less likely to crawl, and more applications can be used at once without drawback. The only potential drawback from using PAE is that, when the computer is at high usage, the memory will have trouble knowing how much to use for cache and how much to use for programs, but this is rare occurrence.

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