Beginning with Linux kernel version 4.1 released in early 2015, Linux on IBM Z is only available as a
64-bit operating system compatible with
z/Architecture mainframes. Previously, Linux on IBM Z was also available as a
32-bit operating system, with
31-bit addressing, compatible with older model mainframes introduced prior to 2000's z900 model. However, the newer 64-bit Linux kernel and 64-bit Linux on IBM Z distributions are still backward compatible with applications compiled for 32-bit Linux on IBM Z. Historically, the Linux kernel architecture designations were "s390" and "s390x" to distinguish between the 32-bit and 64-bit Linux on IBM Z kernels respectively, but "s390" now also refers generally to the one Linux on IBM Z kernel architecture. Linux runs on standard, general purpose mainframe CPs (Central Processors) as well as IFLs (
Integrated Facility for Linux). IFLs are mainframe processors dedicated to running Linux, either natively or under a hypervisor (z/VM or KVM on IBM Z).
Microcode restricts IFLs from running "traditional" workloads, such as
z/OS, but they are physically identical to other IBM Z processors. IFLs are typically less expensive to acquire from IBM than CPs. Linux on IBM Z gives the flexibility of running Linux with the advantages of
fault-tolerant mainframe hardware capable of over 90,000 I/O operations per second and with a
mean time between failure (MTBF) measured in decades. Using virtualization, numerous smaller servers can be combined onto one mainframe, gaining some benefits of centralization and cost reduction, while still allowing specialized servers. Combining full virtualization of the hardware plus lightweight
Virtual Machine containers that run Linux in isolation (somewhat similar in concept to
Docker) result in a platform that supports more virtual servers than any other in a single footprint, which also can lower operating costs. Additional savings can be seen from reduced need for floor space, power, cooling,
networking hardware, and the other
infrastructure needed to support a
data center. IBM mainframes allow transparent use of redundant processor execution steps and integrity checking, which is important for critical applications in certain industries such as banking. Mainframes typically allow
hot swapping of hardware, such as processors and memory. IBM Z provides fault tolerance for all key components, including processors, memory, I/O Interconnect, power supply, channel paths, network cards, and others. Through internal monitoring, possible problems are detected and problem components are designed to be switched over without failing a transaction. In the rare event of failure,
firmware will automatically enable a spare component, disable the failing component, and notify IBM to dispatch a service representative. This is transparent to the operating system, allowing routine repairs to be performed without shutting down the system. Many industries continue to rely on mainframes where they are considered to be the best option in terms of reliability, security, or cost. ==Support==