What is Physical Address Extension?
Physical Address Extension (PAE) is a feature of x86 processors that allows them to access more than 4 gigabytes of physical memory. Introduced by Intel in 1995 with the Pentium Pro processor, PAE was initially intended to support servers and workstations that required more memory than the 4GB limit imposed by the original 32-bit architecture. This article aims to explore the concept of PAE, its significance, and how it has evolved over the years.
The 32-bit x86 architecture, which was widely used in personal computers during the 1990s, was limited to addressing only 4GB of physical memory. This limitation was primarily due to the way memory addresses were stored and managed in the architecture. In a 32-bit system, memory addresses are represented by 32 bits, which can accommodate up to 4GB of memory (2^32 = 4,294,967,296 bytes).
However, as the demand for more memory in computing systems grew, it became clear that the 4GB limit was no longer sufficient. To address this issue, Intel introduced the Physical Address Extension feature. PAE allows the processor to access more than 4GB of physical memory by extending the address bus from 32 bits to 36 bits. This extension provides an additional 4GB of address space, effectively doubling the maximum amount of physical memory that can be accessed.
The introduction of PAE had several implications for the computing industry. Firstly, it enabled servers and workstations to run more memory-intensive applications, such as databases and virtualization software, without the need for 64-bit processors. Secondly, it allowed system vendors to offer more memory options to customers, as they could now support systems with more than 4GB of RAM.
To take advantage of PAE, the operating system must be aware of the feature and enable it. In the case of Windows, for example, PAE support was introduced with Windows Server 2003 and Windows XP Professional x64 Edition. Linux has supported PAE since version 2.4, and most modern operating systems now include PAE support.
Over the years, the significance of PAE has diminished with the rise of 64-bit processors. With 64-bit architectures, the memory addressing limit is no longer a concern, as they can support up to 16 exabytes (2^64 = 18,446,744,073,709,551,616 bytes) of physical memory. However, PAE still plays a role in certain scenarios, such as running 32-bit operating systems on 64-bit hardware or supporting legacy hardware that may not be compatible with 64-bit processors.
In conclusion, Physical Address Extension is a feature that has significantly impacted the computing industry by allowing systems to access more than 4GB of physical memory. While its relevance has decreased with the advent of 64-bit processors, PAE remains an important aspect of the x86 architecture and continues to be supported in modern operating systems.
