Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The IBM System z Application Assist Processor (zAAP), previously known as the zSeries Application Assist Processor, is a mainframe processor introduced by IBM in 2004. zAAP engines are dedicated to running specific Java and XML workloads under z/OS, accelerating performance. zAAPs are available for zSeries 990 and 890 servers and all System z9 and System z10 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 and XML workloads only. As with Integrated Facility for Linux (IFL) and zIIP, zAAPs are not specifically optimized to run Java faster or better. IBM does not change the "software model" or MSU rating on its mainframes with the installation of zAAPs.