Linux on IBM Z or Linux on zSystems is the collective term for the

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

operating system compiled to run on

IBM mainframe IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, IBM dominated the large computer market. Current mainframe computers in IBM's line of business computers are developments of the basic design of th ...

s, especially IBM Z / IBM zSystems and IBM LinuxONE servers. Similar terms which imply the same meaning are ''Linux/390'', ''Linux/390x,'' etc. The three Linux distributions certified for usage on the IBM Z hardware platform are

Red Hat Enterprise Linux Red Hat Enterprise Linux (RHEL) is a commercial open-source Linux distribution developed by Red Hat for the commercial market. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop version ...

SUSE Linux Enterprise Server SUSE Linux Enterprise (often abbreviated to SLE) is a Linux-based operating system developed by SUSE. It is available in two editions, suffixed with Server (SLES) for servers and mainframes, and Desktop (SLED) for workstations and desktop compu ...

, and

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: ''Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All the ...

History

Linux on IBM Z originated as two separate efforts to port Linux to IBM's

System/390 The IBM System/390 is a discontinued mainframe product family implementing the ESA/390, the fifth generation of the System/360 instruction set architecture. The first computers to use the ESA/390 were the Enterprise System/9000 (ES/9000 ...

servers. The first effort, the "Bigfoot" project, developed by Linas Vepstas in late 1998 through early 1999, was an independent distribution and has since been abandoned. IBM published a collection of patches and additions to the Linux 2.2.13

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

on December 18, 1999, to start today's mainline Linux on IBM Z. Formal product announcements quickly followed in 2000, including the

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 IBM Z and IBM LinuxONE machines, IFLs can be used with or without hypervisors such as z/VM and KVM. IFL ...

(IFL) engines.

Think Blue Linux Think Blue Linux (sometimes ''ThinkBlue Linux'') was a port of Linux to IBM S/390 (later, zSeries) mainframe computers, done by the Millenux subsidiary of German company Thinking Objects Software GmbH. The distribution consisted primarily of a ...

was an early mainframe distribution consisting mainly of

Red Hat Red Hat, Inc. is an American software company that provides open source software products to enterprises. Founded in 1993, Red Hat has its corporate headquarters in Raleigh, North Carolina, with other offices worldwide. Red Hat has become ass ...

packages added to the IBM kernel. Commercial Linux distributors introduced mainframe editions very quickly after the initial kernel work. At the start of IBM's involvement, Linux patches for IBM Z included some ''object code only'' (OCO) modules, without source code. Soon after IBM replaced the OCO modules with

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...

modules. Linux on IBM Z is

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...

under the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was th ...

. According to IBM, by May, 2006, over 1,700 customers were running Linux on their mainframes.

Virtualization

Virtualization In computing, virtualization or virtualisation (sometimes abbreviated v12n, a numeronym) is the act of creating a virtual (rather than actual) version of something at the same abstraction level, including virtual computer hardware platforms, stor ...

is required by default on IBM Z; there is no option to run Linux on IBM Z without some degree of virtualization. (Only the very first 64-bit mainframe models, the z900 and z800, included a non-virtualized "basic mode.") First layer virtualization is provided by the Processor Resource and System Manager (

PR/SM A logical partition (LPAR) is a subset of a computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate instance of an operating ...

) to deploy one or more Logical Partitions (LPARs). Each LPAR supports a variety of operating systems including Linux on IBM Z. A

hypervisor A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is calle ...

called z/VM can also be run as the second layer virtualization in LPARs to create as many virtual machines (VMs) as there are resources assigned to the LPARs to support them. KVM on IBM Z is another hypervisor option. When Linux applications in an LPAR access data and applications in other LPARs such as

CICS IBM CICS (Customer Information Control System) is a family of mixed-language application servers that provide online transaction management and connectivity for applications on IBM mainframe systems under z/OS and z/VSE. CICS family products ...

IBM Db2 Db2 is a family of data management products, including database servers, developed by IBM. It initially supported the relational model, but was extended to support object–relational features and non-relational structures like JSON a ...

, IMS,

, and other mainframe subsystems running on the same physical mainframe, they can utilize

HiperSocket HiperSockets is an IBM technology for high-speed communications between partitions on a server with a hypervisor. The term is most commonly associated with System z9 and later IBM Z mainframes which can provide in-memory TCP/IP connections betwe ...

s – fast, memory-only

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

connections. As compared to TCP/IP over standard

network interface card A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network. Ear ...

s (NICs, also known as Open System Adapters (OSAs) in mainframes), HiperSockets can improve end-user responsiveness (reduce network latency and processing overhead), security (since there's no network connection to intercept), and reliability (since there's no network connection to lose). With the zEC12, zBC12, and later models, the HiperSocket concept is extended beyond the physical machine boundary via an

RDMA over Converged Ethernet RDMA over Converged Ethernet (RoCE) or InfiniBand over Ethernet (IBoE) is a network protocol that allows remote direct memory access (RDMA) over an Ethernet network. It does this by encapsulating an InfiniBand (IB) transport packet over Ethernet. ...

(RoCE) adapter to facilitate a secure and high speed inter-system communication. Applications in LPAR A in system A can thus use HiperSockets to communicate with applications in LPAR B in system B to ensure the security and performance attributes.

Hardware

Beginning with Linux kernel version 4.1 released in early 2015, Linux on IBM Z is only available as a

64-bit In computer architecture, 64-bit Integer (computer science), integers, memory addresses, or other Data (computing), data units are those that are 64 bits wide. Also, 64-bit central processing unit, CPUs and arithmetic logic unit, ALUs are those ...

operating system compatible with

z/Architecture z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architecture-b ...

mainframes. Previously Linux on IBM Z was also available as a

32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculation ...

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 (

). IFLs are mainframe processors dedicated to running Linux, either natively or under a hypervisor (z/VM or KVM on IBM Z).

Microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a laye ...

restricts IFLs from running "traditional" workloads, such as

z/OS z/OS is a 64-bit operating system for IBM z/Architecture mainframes, introduced by IBM in October 2000. It derives from and is the successor to OS/390, which in turn was preceded by a string of MVS versions.Starting with the earliest: * O ...

, but they are physically identical to other IBM Z processors. IFLs are typically less expensive to acquire from IBM than CPs.

Advantages

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. Instead of

paravirtualization In computing, paravirtualization or para-virtualization is a virtualization technique that presents a software interface to the virtual machines which is similar, yet not identical, to the underlying hardware–software interface. The intent o ...

, IBM mainframes use

full virtualization In computer science, virtualization is a modern technique developed in late 1990s and is different from simulation and emulation. Virtualization employs techniques used to create instances of an environment, as opposed to simulation, which model ...

, which permits workload density far greater than paravirtualization does. Combining full virtualization of the hardware plus lightweight

Virtual Machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...

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 Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...

needed to support a

data center A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunic ...

. 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 even failing a single 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.

Pricing and costs

Linux on IBM Z is not generally appropriate on-premises for small businesses that would have fewer than about 10 distributed Linux servers, although some expensive per-processor licensed software can quickly reduce that

rule of thumb In English, the phrase ''rule of thumb'' refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various t ...

. Most software vendors, including IBM, treat the highly virtualized IFLs just like non-virtualized processors on other platforms for licensing purposes. In other words, a single IFL running scores of Linux instances still typically counts as one "ordinary" CPU, at the same CPU price, for software licensing. Test, development, quality assurance, training, and redundant production server instances can all run on one IFL (or more IFLs, but only if needed for peak demand performance capacity). Thus, beyond some minimum threshold, Linux on IBM Z can quickly become cost-advantageous when factoring in labor and software costs. The cost equation for Linux on IBM Z is not always well understood and is controversial, and many businesses and governments have difficulty measuring, much less basing decisions on, software, labor, and other costs (such as the costs of outage and security breaches). Acquisition costs are often more visible, and small, non-scalable servers are "cheap." Nonetheless, non-acquisition costs are no less real and are usually far greater than hardware acquisition prices. Also, individual users and departments within larger businesses and governments sometimes have difficulty sharing computing infrastructure (or any other resources, for that matter), citing a loss of control. Server centralization, as Linux on IBM Z provides, might reward cooperation with better service and lower costs, but that's not to say that cooperation is always easily accomplished within a corporate bureaucracy. Linux on IBM Z also supports less expensive disk storage devices than z/OS because Linux does not require FICON or ESCON attachment, although z/OS may use disk space more efficiently, on balance, due to hardware-assisted database compression common on z/OS and the smaller number of operating system instances z/OS typically requires. There are also some operational advantages using some FICON-attached storage with Linux on IBM Z, for example support for z/VM Live Guest Relocation.

Appropriate workloads

Mainframe characteristics are designed for such business workloads as transaction processing (especially in conjunction with concurrent, high volume batch processing) and large database management. Mainframe design traditionally emphasizes "balanced" performance for all computing elements including input/output, implemented via

channel I/O In computing, channel I/O is a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers. In the past, channels were generally implemented with cus ...

. Mainframes offload I/O, system accounting, and other non-core computing tasks from the main CPUs as much as possible, and z/Architecture additionally offloads cryptographic calculations. For example, in a single IBM z13 machine up to 141 processor cores are available to configure as IFLs. However, every such machine also has 27 additional main cores: 2 as spares, 1 for firmware support, and the remainder running system accounting and I/O support tasks. In addition, each I/O adapter typically has two

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

processors, and a z13 supports hundreds of I/O adapters. There are also separate processors handling memory and cache control tasks, environmental monitoring, and internal interconnections, as examples. Historically, mainframes in general, and Linux on IBM Z in particular, did not execute "CPU-intensive" single task computations with notably high performance compared to certain other platforms with a few notable exceptions such as cryptographic calculations. Examples included most scientific simulations,

weather forecasting Weather forecasting is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather informally for millennia a ...

, and

molecular modeling Molecular modelling encompasses all methods, theoretical and computational, used to model or mimic the behaviour of molecules. The methods are used in the fields of computational chemistry, drug design, computational biology and materials scien ...

Supercomputers A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...

, including Linux-based supercomputers, excel at these workloads. This bifurcation between mainframes and other platforms has significantly blurred in recent years, starting with the introduction of 2008's System z10, a machine based on quad-core 4.4 GHz processors with hardware decimal floating point. As mainframe processor technology has continued to evolve, and especially with the introduction of the IBM LinuxONE and IBM z13 models in 2015, IBM has started promoting its mainframes as ideal platforms to run real-time analytics and other computationally intensive tasks that mainframes did not historically run well. Mainframes do not provide graphics or sound adapters, and are as such ill-suited for

digital media Digital media is any communication media that operate in conjunction with various encoded machine-readable data formats. Digital media can be created, viewed, distributed, modified, listened to, and preserved on a digital electronics device. ' ...

editing or

computer-aided design Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve c ...

(CAD) except perhaps in support roles (e.g. content storage, parts inventories, metadata management, security services, etc.)

Support

Like all other versions of Linux, Linux on IBM Z is governed by the GPL

license. Complete Linux on IBM Z

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the wo ...

is available from numerous parties on a free and equal basis, and architectural support is part of the main Linux kernel effort. IBM assigns several of its programmers to the community effort, but IBM is by no means the only participant. Though there are no obstacles to running any Linux on IBM Z distribution on an IBM z System, IBM routinely tests three particular Linux on IBM Z distributions:

SUSE SUSE ( , ) is a German-based multinational open-source software company that develops and sells Linux products to business customers. Founded in 1992, it was the first company to market Linux for enterprise. It is the developer of SUSE Linux Ent ...

, and starting in 2015,

Canonical The adjective canonical is applied in many contexts to mean "according to the canon" the standard, rule or primary source that is accepted as authoritative for the body of knowledge or literature in that context. In mathematics, "canonical example ...

Ubuntu Linux Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: ''Desktop'', '' Server'', and ''Core'' for Internet of things devices and robots. All ...

. Other notable Linux on IBM Z distributions include

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of D ...

(upstream for Ubuntu),

Fedora A fedora () is a hat with a soft brim and indented crown.Kilgour, Ruth Edwards (1958). ''A Pageant of Hats Ancient and Modern''. R. M. McBride Company. It is typically creased lengthwise down the crown and "pinched" near the front on both sides ...

(upstream for RHEL),

Slackware Slackware is a Linux distribution created by Patrick Volkerding in 1993. Originally based on Softlanding Linux System, Slackware has been the basis for many other Linux distributions, most notably the first versions of SUSE Linux distributions ...

CentOS CentOS (, from Community Enterprise Operating System; also known as CentOS Linux) is a Linux distribution that provides a free and open-source community-supported computing platform, functionally compatible with its upstream source, Red Hat En ...

Alpine Linux Alpine Linux is a Linux distribution designed to be small, simple and secure. Alpine Linux uses musl, BusyBox and OpenRC instead of the more commonly used glibc, GNU Core Utilities and systemd respectively.

and Gentoo. Nearly every free or open-source software package available for Linux generally is available for Linux on IBM Z, including

Apache HTTP Server The Apache HTTP Server ( ) is a free and open-source cross-platform web server software, released under the terms of Apache License 2.0. Apache is developed and maintained by an open community of developers under the auspices of the Apache So ...

Samba software Samba is a free software re-implementation of the SMB networking protocol, and was originally developed by Andrew Tridgell. Samba provides file and print services for various Microsoft Windows clients and can integrate with a Microsoft W ...

JBoss WildFly, formerly known as JBoss AS, or simply JBoss, is an application server written by JBoss, now developed by Red Hat. WildFly is written in Java and implements the Java Platform, Enterprise Edition (Java EE) specification. It runs on multip ...

PostgreSQL PostgreSQL (, ), also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to its origins as a successor to the In ...

MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database o ...

PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group ...

Python programming language Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. Python is dynamically-typed and garbage-collected. It supports multiple programming p ...

Concurrent Versions System Concurrent Versions System (CVS, also known as the Concurrent Versioning System) is a revision control system originally developed by Dick Grune in July 1986. CVS operates as a front end to RCS, an earlier system which operates on single fil ...

(CVS),

GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free software ...

(GCC),

LLVM LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture. LLVM is designed around a language-independent intermediate represen ...

, and

Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offici ...

Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH ...

, among many others. Red Hat and SUSE offer mainline support for their distributions running Linux on IBM Z. In 2015 Canonical announced plans to offer official support for its distribution starting in early 2016.

IBM Global Services IBM Consulting, rebranded in 2021 from IBM Global Business Services, is the professional services and consulting arm of IBM. IBM Consulting provides services to companies, global government organizations, non-profits and NGOs. IBM Consulting IBM ...

also offers support contracts, including 24x7 coverage. Some standard Linux software applications are readily available pre-compiled, including popular closed-source enterprise software packages such as

WebSphere IBM WebSphere refers to a brand of proprietary computer software products in the genre of enterprise software known as "application and integration middleware". These software products are used by end-users to create and integrate applications wi ...

and

Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word '' ...

databases and applications,

SAP R/3 SAP R/3 is the former name of the enterprise resource planning software produced by the German corporation SAP AG (now SAP SE). It is an enterprise-wide information system designed to coordinate all the resources, information, and activities needed ...

SAP ERP SAP ERP is an enterprise resource planning software developed by the German company SAP SE. SAP ERP incorporates the key business functions of an organization. The latest version of SAP ERP (V.6.0) was made available in 2006. The most recent SA ...

, and IBM's

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...

Developer's Kit (JDK), to name only a few.

Developer resources

IBM offers resources to developers wishing to target Linux for z: * The Linux Test Drive, a free program granting a single Linux on IBM Z virtual machine for 30 days. * The IBM Systems Application Advantage for Linux (

Chiphopper Chiphopper is a component of the IBM eServer products specifically tailored to the Linux operating system. IBM developed the server products in a collaborative effort with Red Hat and Novell of SUSE Linux ownership at the time. The official name of ...

), a developer program to help developers write and publish cross-platform Linux software. * The Community Development System for Linux on IBM Z (CDSL) program, a platform for providing

developers a platform for porting to Linux on System z. * The Linux Remote Development Program, a fee-based extended developer support program. Linux on IBM Z supports

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...

and

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

just like any other Linux distribution—it is not an

EBCDIC Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding six- ...

-based operating system. However, for convenience Linux is able to read kernel parameters in EBCDIC. z/VM takes advantage of this capability. Porting Linux applications to Linux on IBM Z is fairly straightforward. Potential issues include

endianness In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...

(Linux on IBM Z is big-endian) and reliance on non-portable libraries particularly if source code is not available. Programs can be easily cross compiled to z/Architecture binaries on non-mainframe Linux systems.

Emulators

There are at least three software-based IBM Z mainframe

emulator In computing, an emulator is Computer hardware, hardware or software that enables one computer system (called the ''host'') to behave like another computer system (called the ''guest''). An emulator typically enables the host system to run so ...

s. * FLEX-ES from Fundamental Software is a commercially offered option, limited to 31-bit addressing. * The open source

Hercules emulator Hercules is a computer emulator allowing software written for IBM mainframe computers (System/370, System/390, and zSeries/System z) and for plug compatible mainframes (such as Amdahl machines) to run on other types of computer hardware, nota ...

supports Linux on IBM Z (and can even run on Linux on System z itself). * In 2010, IBM introduced the Rational Developer for System z Unit Test Feature (now called Rational Development and Test Environment for z, or sometimes RDTz for short) which provides a restricted use execution environment that can run on X86 hardware. IBM's license terms limit use of RDTz to certain application development tasks, not including final pre-production compiling or pre-production testing (such as stress testing). RDTz includes z/OS (with common middleware) and is also compatible with Linux on IBM Z.

History

Virtualization

Hardware

Advantages

Pricing and costs

Appropriate workloads

Support

Developer resources

Emulators

See also

References

External links