Address Windowing Extensions (AWE) is a
Microsoft Windows application programming interface 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 comput ...
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 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 spa ...
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 ...
and
engineering
Engineering is the use of scientific method, 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 rang ...
software
Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work.
...
, 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 d ...
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 storag ...
.
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 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 official ...
as a new API superseding the
PSE36 method (from the
Windows NT 4.0 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 wor ...
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.
See also
*
Expanded Memory Specification (EMS)
*
Physical Address Extension (PAE)
References
External links
Address Windowing Extensionson
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