Integrated Facility for Linux

The Integrated Facility for Linux (IFL) is an IBM mainframe and Power Systems processor dedicated to running the Linux operating system. On System z, it can be used with or without z/VM. IFLs are one of three types of IBM mainframe processors expressly designed to reduce software costs. (The other types are zAAP for Java code and zIIP for DB2). Microcode restricts IFLs to Linux workload by omitting some processor instructions not used by the Linux kernel. As with zAAPs and zIIPs, IFLs are not specifically optimized to run Linux faster or better.

IBM introduced IFLs on September 29, 2000. At the same time, IBM introduced a special Linux-only VM-like product, called the S/390 Virtual Image Facility for Linux, to cater to IT staff previously unfamiliar with IBM mainframes. IBM soon discovered that z/VM was not too difficult for new IT staff to learn (and worked better), so IBM discontinued S/390 Virtual Image Facility for Linux in April 2002.

Potential customers can purchase IFLs for all IBM mainframes as far back as the G5 series. Fujitsu and Hitachi also offered IFLs on certain models. An IFL is not required to run Linux – Linux runs on general purpose processors (CPs) as well.

On Power Systems IFLs have a special pricing for the hardware and also for IBM software different from the standard pricing for AIX.

...
Wikipedia