Z Application Assist Processor
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- The correct title of this article is z Application Assist Processor. The initial letter is shown capitalized due to technical restrictions.
IBM System z Application Assist Processor (zAAP) is the zSeries Application Assist Processor, a 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 all System z9 servers.
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 do not incur software license charges for their zAAPs, reducing their costs of running Java-based applications. The number of zAAPs cannot exceed the number of CPs (unrestricted, general purpose engines) within a zSeries/z9 server.
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. IBM modified the z/OS dispatcher and Workload Manager (WLM) to switch pure Java workload over to the dedicated engines. These modifications are completely transparent to Java applications. However, because Java must at least occasionally call native system services (I/O services, for example), some conventional system capacity (CP) must be available to initiate and sustain a zAAP engine. Major software subsystems that could benefit from zAAP (i.e. that can run Java workloads) include WebSphere Application Server, WebSphere Business Integration Server Foundation, WebSphere Process Server, WebSphere Message Broker, DB2, CICS, CICS Transaction Gateway, IMS, and z/OS UNIX System Services, 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 on a zSeries 990 (2084-304/A08 with two zAAPs). This deployment is probably a mainframe record for speed of both development and adoption, since IBM only began its zAAP design project in 2003.
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.
