Address Windowing Extensions (AWE) is a

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...

application programming interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...

that allows a 32-bit software

application Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...

to access more

physical memory Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a compute ...

than it has virtual address space, even in excess of the 4 GB limit. The process of mapping an application's virtual address space to physical memory under AWE is known as "windowing", and is similar to the

overlay Overlay may refer to: Computers *Overlay network, a computer network which is built on top of another network *Hardware overlay, one type of video overlay that uses memory dedicated to the application *Another term for exec, replacing one process ...

concept of other environments. AWE is beneficial to certain

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...

-intensive applications, such as

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

management systems and

scientific Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...

and

engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...

, that need to manipulate very large

data set A data set (or dataset) is a collection of data. In the case of tabular data, a data set corresponds to one or more database tables, where every column of a table represents a particular variable, and each row corresponds to a given record of the ...

s while minimizing

paging In computer operating systems, memory paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage ...

. The application reserves a region, or "window" of virtual address space, and allocates one or more regions of physical memory. Using the AWE API, the application can map the virtual window to any one of the physical regions. The application can reserve more than one virtual address space and map it to any of the allocated regions of physical memory, as long as the number of bytes reserved in the virtual address space matches that of the physical memory region. An application must have the Lock Pages in Memory privilege to use AWE. On 32-bit systems, AWE depends on

Physical Address Extension In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension, 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 proces ...

support when reserving memory above 4 GB. AWE was first introduced in

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was the direct successor to Windows NT 4.0, and was released to manufacturing on December 15, 1999, and was offici ...

as a new API superseding the PSE36 method (from the

Windows NT 4.0 Windows NT 4.0 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It is the direct successor to Windows NT 3.51, which was released to manufacturing on July 31, 1996, and then to retail ...

Enterprise Edition) of accessing more than 4 GB of memory, which was no longer supported in Windows 2000. Among the first applications to make use of AWE were

Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ...

8.1.6 and

Microsoft SQL Server Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ...

2000. If the boot flag is used to repartition the 32-bit virtual address space (from the 2 GB kernel and 2 GB userland) to 3 GB userland, then AWE is limited to accessing 16 GB of physical memory. This limitation is because with only one GB reserved for the kernel, there isn't enough memory for the page table entries to map more than 16 GB of memory. Additional restrictions on the maximum amount of memory addressable thorough AWE are imposed by the Windows licensing scheme. For example, Windows 2000 Advanced Server was limited to 8 GB, while Windows 2000 Data Center Server supported 64 GB. An article published in Dr. Dobb's Journal in 2004 noted that memory allocated using Address Windowing Extensions will not be written to the pagefile, and suggested that AWE regions could therefore be used as a way of protecting sensitive application data such as encryption keys.

References

External links

Address Windowing Extensions
on

MSDN Microsoft Developer Network (MSDN) was the division of Microsoft responsible for managing the firm's relationship with developers and testers, such as hardware developers interested in the operating system (OS), and software developers developing ...

Address Windowing Extensions
Coding Example {{Microsoft APIs Microsoft application programming interfaces Windows NT architecture X86 memory management

See also

References

External links