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zAAP is the zSeries Application Assist Processor, a new mainframe processor introduced by IBM in 2004. zAAP engines are dedicated to running Java workloads under z/OS, accelerating performance. zAAPs are available for zSeries 990 and 890 servers (and presumably future zSeries systems).
Currently a zAAP engine contains the same underlying hardware as any other mainframe engine. However, IBM uses microcode to limit code execution to Java workloads only. IBM does not change the "software model" or MSU rating on its mainframes with the installation of zAAPs. Consequently IBM's customers typically do not incur software license charges for their zAAPs, reducing their costs of running Java-based applications. IBM's microcode allows no more than one zAAP per CP (unrestricted mainframe processor).
IBM made the zAAP hardware (i.e. microcode) generally available on June 30, 2004, although the required z/OS release was not generally available until September 24, 2004. (zAAPs work with z/OS V1R6 and higher, and Java 1.4.1 and higher.) Major software subsystems that could benefit from zAAP include WebSphere Application Server, WebSphere Business Integration Server Foundation, DB2, CICS, and IMS, among others.
The first commercial production workload for zAAP began on September 1, 2004, at an undisclosed Midwestern U.S. insurance company performing claims processing. The company used Java 1.4.2, WebSphere Application Server Version 5.1, and a near-final z/OS V1R6 build.
zAAP is not the first processor technology dedicated to a specific programming language or even to Java. Other examples of Java processors include aJile Systems' aJ-100 and Sun's picoJava. However, zAAP is apparently unique to large-scale commercial Java processing.