Linux is a family of free and open-source software operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is packaged in a Linux distribution. Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy. Popular Linux distributions include Debian and Ubuntu. Commercial distributions include SUSE Linux Enterprise Server. Desktop Linux distributions include a windowing system such as X11 or Wayland, a desktop environment such as GNOME or KDE Plasma. Distributions intended for servers may omit graphics altogether, include a solution stack such as LAMP; because Linux is redistributable, anyone may create a distribution for any purpose. Linux was developed for personal computers based on the Intel x86 architecture, but has since been ported to more platforms than any other operating system.
Linux is the leading operating system on servers and other big iron systems such as mainframe computers, the only OS used on TOP500 supercomputers. It is used by around 2.3 percent of desktop computers. The Chromebook, which runs the Linux kernel-based Chrome OS, dominates the US K–12 education market and represents nearly 20 percent of sub-$300 notebook sales in the US. Linux runs on embedded systems, i.e. devices whose operating system is built into the firmware and is tailored to the system. This includes routers, automation controls, digital video recorders, video game consoles, smartwatches. Many smartphones and tablet computers run other Linux derivatives; because of the dominance of Android on smartphones, Linux has the largest installed base of all general-purpose operating systems. Linux is one of the most prominent examples of open-source software collaboration; the source code may be used and distributed—commercially or non-commercially—by anyone under the terms of its respective licenses, such as the GNU General Public License.
The Unix operating system was conceived and implemented in 1969, at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, Joe Ossanna. First released in 1971, Unix was written in assembly language, as was common practice at the time. In a key pioneering approach in 1973, it was rewritten in the C programming language by Dennis Ritchie; the availability of a high-level language implementation of Unix made its porting to different computer platforms easier. Due to an earlier antitrust case forbidding it from entering the computer business, AT&T was required to license the operating system's source code to anyone who asked; as a result, Unix grew and became adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs; the GNU Project, started in 1983 by Richard Stallman, had the goal of creating a "complete Unix-compatible software system" composed of free software. Work began in 1984. In 1985, Stallman started the Free Software Foundation and wrote the GNU General Public License in 1989.
By the early 1990s, many of the programs required in an operating system were completed, although low-level elements such as device drivers and the kernel, called GNU/Hurd, were stalled and incomplete. Linus Torvalds has stated that if the GNU kernel had been available at the time, he would not have decided to write his own. Although not released until 1992, due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has stated that if 386BSD had been available at the time, he would not have created Linux. MINIX was created by Andrew S. Tanenbaum, a computer science professor, released in 1987 as a minimal Unix-like operating system targeted at students and others who wanted to learn the operating system principles. Although the complete source code of MINIX was available, the licensing terms prevented it from being free software until the licensing changed in April 2000. In 1991, while attending the University of Helsinki, Torvalds became curious about operating systems.
Frustrated by the licensing of MINIX, which at the time limited it to educational use only, he began to work on his own operating system kernel, which became the Linux kernel. Torvalds began the development of the Linux kernel on MINIX and applications written for MINIX were used on Linux. Linux matured and further Linux kernel development took place on Linux systems. GNU applications replaced all MINIX components, because it was advantageous to use the available code from the GNU Project with the fledgling operating system. Torvalds initiated a switch from his original license, which prohibited commercial redistribution, to the GNU GPL. Developers worked to integrate GNU components with the Linux kernel, making a functional and free operating system. Linus Torvalds had wanted to call his invention "Freax", a portmant
International Organization for Standardization
The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and commercial standards, it is headquartered in Geneva and works in 164 countries. It was one of the first organizations granted general consultative status with the United Nations Economic and Social Council; the International Organization for Standardization is an independent, non-governmental organization, the members of which are the standards organizations of the 164 member countries. It is the world's largest developer of voluntary international standards and facilitates world trade by providing common standards between nations. Over twenty thousand standards have been set covering everything from manufactured products and technology to food safety and healthcare. Use of the standards aids in the creation of products and services that are safe, reliable and of good quality.
The standards help businesses increase productivity while minimizing errors and waste. By enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis; the standards serve to safeguard consumers and the end-users of products and services, ensuring that certified products conform to the minimum standards set internationally. The three official languages of the ISO are English and Russian; the name of the organization in French is Organisation internationale de normalisation, in Russian, Международная организация по стандартизации. ISO is not an acronym; the organization adopted ISO as its abbreviated name in reference to the Greek word isos, as its name in the three official languages would have different acronyms. During the founding meetings of the new organization, the Greek word explanation was not invoked, so this meaning may have been made public later. ISO gives this explanation of the name: "Because'International Organization for Standardization' would have different acronyms in different languages, our founders decided to give it the short form ISO.
ISO is derived from the Greek isos, meaning equal. Whatever the country, whatever the language, the short form of our name is always ISO."Both the name ISO and the ISO logo are registered trademarks, their use is restricted. The organization today known as ISO began in 1928 as the International Federation of the National Standardizing Associations, it was suspended in 1942 during World War II, but after the war ISA was approached by the formed United Nations Standards Coordinating Committee with a proposal to form a new global standards body. In October 1946, ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the new International Organization for Standardization. ISO is a voluntary organization whose members are recognized authorities on standards, each one representing one country. Members meet annually at a General Assembly to discuss ISO's strategic objectives; the organization is coordinated by a Central Secretariat based in Geneva. A Council with a rotating membership of 20 member bodies provides guidance and governance, including setting the Central Secretariat's annual budget.
The Technical Management Board is responsible for over 250 technical committees, who develop the ISO standards. ISO has formed two joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. ISO/IEC Joint Technical Committee 1 was created in 1987 to "evelop, maintain and facilitate IT standards", where IT refers to information technology. ISO/IEC Joint Technical Committee 2 was created in 2009 for the purpose of "tandardization in the field of energy efficiency and renewable energy sources". ISO has 163 national members. ISO has three membership categories: Member bodies are national bodies considered the most representative standards body in each country; these are the only members of ISO. Correspondent members are countries; these members do not participate in standards promulgation. Subscriber members are countries with small economies, they can follow the development of standards. Participating members are called "P" members, as opposed to observing members, who are called "O" members.
ISO is funded by a combination of: Organizations that manage the specific projects or loan experts to participate in the technical work. Subscriptions from member bodies; these subscriptions are in proportion to each country's gross national trade figures. Sale of standards. ISO's main products are international standards. ISO publishes technical reports, technical specifications, publicly available specifications, technical corrigenda, guides. International standards These are designated using the format ISO nnnnn: Title, where nnnnn is the number of the standard, p is an optional part number, yyyy is the year published, Title describes the subject. IEC for International Electrotechnical Commission is included if the standard results from the work of ISO/IEC JTC1. ASTM is used for standards developed in cooperation with ASTM International. Yyyy and IS are not used for an incomplete or unpublished standard and may under some
HP-UX is Hewlett Packard Enterprise's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984. Recent versions support the HP 9000 series of computer systems, based on the PA-RISC instruction set architecture, HP Integrity systems, based on Intel's Itanium architecture. Earlier versions of HP-UX supported the HP Integral PC and HP 9000 Series 200, 300, 400 computer systems based on the Motorola 68000 series of processors, as well as the HP 9000 Series 500 computers based on HP's proprietary FOCUS architecture. HP-UX was the first Unix to offer access control lists for file access permissions as an alternative to the standard Unix permissions system. HP-UX was among the first Unix systems to include a built-in logical volume manager. HP has had a long partnership with Veritas Software, uses VxFS as the primary file system, it is one of six commercial operating systems that have versions certified to The Open Group's UNIX 03 standard. HP-UX 11i offers a common root disk for its clustered file system.
HP Serviceguard is the cluster solution for HP-UX. HP Global Workload Management adjusts workloads to optimize performance, integrates with Instant Capacity on Demand so installed resources can be paid for in 30-minute increments as needed for peak workload demands. HP-UX offers operating system-level virtualization features such as hardware partitions, isolated OS virtual partitions on cell-based servers, HP Integrity Virtual Machines on all Integrity servers. HPVM supports guests running on HP-UX 11i v3 hosts – guests can run Linux, OpenVMS 8.4 or HP-UX. HP supports online VM guest migration, where encryption can secure the guest contents during migration. HP-UX 11i v3 scales as follows: 256 processor cores 8 TB main memory 32 TB maximum file system 16 TB maximum file size 128 million ZB—16 million logical units each up to 8ZB. "HP-UX 11i v3". Retrieved 2017-10-31; the 11i v2 release introduced kernel-based intrusion detection, strong random number generation, stack buffer overflow protection, security partitioning, role-based access management, various open-source security tools.
HP classifies the operating system's security features into three categories: data and identity: Release 6.x introduced the context dependent files feature, a method of allowing a fileserver to serve different configurations and binaries to different client machines in a heterogeneous environment. A directory containing such files had its suid bit set and was made hidden from both ordinary and root processes under normal use; such a scheme was sometimes exploited by intruders to hide malicious data. CDFs and the CDF filesystem were dropped with release 10.0. HP-UX operating systems supports a variety of PA-RISC systems; the 11.0 added support for Integrity-based servers for the transition from PA-RISC to Itanium. HP-UX 11i v1.5 is the first version. On the introduction of HP-UX 11i v2 the operating system supported both of these architectures. HP-UX 11i supports HP Integrity Servers of HP BL server blade family; these servers use the Intel Itanium architecture. HP-UX 11i v2 and 11i v3 support HP's CX series servers.
CX stands for carrier grade and is used for telco industry with -48V DC support and is NEBS certified. Both of these systems are discontinued. HP-UX supports HP's RX series of servers. Prior to the release of HP-UX version 11.11, HP used a decimal version numbering scheme with the first number giving the major release and the number following the decimal showing the minor release. With 11.11, HP made a marketing decision to name their releases 11i followed by a v for the version. The i was intended to indicate the OS is Internet-enabled, but the effective result was a dual version-numbering scheme. 1.0 First release for HP 9000 Series 500. HP-UX for Series 500 was different that HP-UX for any other HP machines, as it was layered atop a Series 500 specific operating system called SUNOS. 1.0 AT&T System III based. Support for the HP Integral PC; the kernel runs from ROM. 2.0 First release for HP's early Motorola 68000-based workstations 5.0 ROM-based AT&T System V for the HP Integral PC. Distinct from a HP-UX 5.x for Series 200/300.
3.x HP 9000 Series 600/800 only. Note: 2.x/3.x were developed in parallel with 5.x/6.x, so, for example, 3.x was contemporary with 6.x. The two lines were united at HP-UX 7.x. 6.x Support for HP 9000 Series 300 only. Introduced sockets from 4.3BSD. This version introduced the above-discussed context dependent files, which were removed in release 10 because of their security risks. 7.x Support for HP 9000 Series 300/400, 600/700 /800 HP systems. Provided OSF/Motif. 8.x Support for HP 9000 Series 300/400 600/700/800 systems. Shared libraries introduced. 9.x 9.00, 9.02, 9.04, 9.01, 9.03, 9.05, 9.07, 9.08, 9.09, 9.09+, 9.10. These provided support for the HP 9000 800 systems. Introduced System Administration Manager; the Logical Volume Manager was presented in 9.00 for the Series 800. 10.0 This major release saw a convergence of the operating system between the HP 9000 Series 700 and Series 800 systems, dropping suppor
Version 7 Unix
Seventh Edition Unix called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T Corporation in the early 1980s. V7 was developed for Digital Equipment Corporation's PDP-11 minicomputers and was ported to other platforms. Unix versions from Bell Labs were designated by the edition of the user's manual with which they were accompanied. Released in 1979, the Seventh Edition was preceded by Sixth Edition, the first version licensed to commercial users. Development of the Research Unix line continued with the Eighth Edition, which incorporated development from 4.1BSD, through the Tenth Edition, after which the Bell Labs researchers concentrated on developing Plan 9. V7 was the first portable version of Unix; as this was the era of minicomputers, with their many architectural variations, the beginning of the market for 16-bit microprocessors, many ports were completed within the first few years of its release.
The first Sun workstations ran a V7 port by UniSoft. The VAX port of V7, called UNIX/32V, was the direct ancestor of the popular 4BSD family of Unix systems; the group at University of Wollongong that had ported V6 to the Interdata 7/32 ported V7 to that machine as well. Interdata sold the port as Edition VII. DEC distributed their own PDP-11 version of V7, called V7M. V7M, developed by DEC's original Unix Engineering Group, contained many enhancements to the kernel for the PDP-11 line of computers including improved hardware error recovery and many additional device drivers. UEG evolved into the group that developed Ultrix. Due to its power yet elegant simplicity, many old-time Unix users remember V7 as the pinnacle of Unix development and have dubbed it "the last true Unix", an improvement over all preceding and following Unices. At the time of its release, its extended feature set came at the expense of a decrease in performance compared to V6, to be corrected by the user community; the number of system calls in Version 7 was only around 50, while Unix and Unix-like systems continued to add many more: Version 7 of the Research UNIX System provided about 50 system calls, 4.4BSD provided about 110, SVR4 had around 120.
The exact number of system calls varies depending on the operating system version. More recent systems have seen incredible growth in the number of supported system calls. Linux 3.2.0 has 380 system calls and FreeBSD 8.0 has over 450. In 2002, Caldera International released V7 as FOSS under a permissive BSD-like software license. Bootable images for V7 can still be downloaded today, can be run on modern hosts using PDP-11 emulators such as SIMH. An x86 port has been developed by Nordier & Associates. Paul Allen maintains several publicly accessible historic computer systems, including a PDP-11/70 running Unix Version 7. Request a login from Living Computers: Museum + Labs and try running Version 7 Unix on the original equipment. Many new features were introduced in Version 7. Programming tools: lex and make; the Portable C Compiler was provided along with the earlier, C compiler by Ritchie. These first appeared in the Research Unix lineage in Version 7, although early versions of some of them had been picked up by PWB/UNIX.
New commands: the Bourne shell, at, calendar, f77, tar, touch Networking support, in the form of uucp and Datakit New system calls: access, alarm, exece, lseek, utime New library calls: The new stdio routines, getenv, popen/system Environment variables A maximum file size of just over one gigabyte, through a system of indirect addressing A feature that did not survive long was a second way to do inter-process communication: multiplexed files. A process could create a special type of file with the mpx system call. Mpx files were considered experimental, not enabled in the default kernel, disappeared from versions, which offered sockets or CB UNIX's IPC facilities instead. Version 6 Unix Seventh Edition Unix terminal interface Ancient UNIX Unix Seventh Edition manual Browsable source code PDP Unix Preservation Society
Silicon Graphics, Inc. was an American high-performance computing manufacturer, producing computer hardware and software. Founded in Mountain View, California in November 1981 by Jim Clark, its initial market was 3D graphics computer workstations, but its products and market positions developed over time. Early systems were based on the Geometry Engine that Clark and Marc Hannah had developed at Stanford University, were derived from Clark's broader background in computer graphics; the Geometry Engine was the first very-large-scale integration implementation of a geometry pipeline, specialized hardware that accelerated the "inner-loop" geometric computations needed to display three-dimensional images. For much of its history, the company focused on 3D imaging and was a major supplier of both hardware and software in this market. Silicon Graphics reincorporated as a Delaware corporation in January 1990. Through the mid to late-1990s, the improving performance of commodity Wintel machines began to erode SGI's stronghold in the 3D market.
The porting of Maya to other platforms is a major event in this process. SGI made several attempts to address this, including a disastrous move from their existing MIPS platforms to the Intel Itanium, as well as introducing their own Linux-based Intel IA-32 based workstations and servers that failed in the market. In the mid-2000s the company repositioned itself as a supercomputer vendor, a move that failed. On April 1, 2009, SGI filed for Chapter 11 bankruptcy protection and announced that it would sell all of its assets to Rackable Systems, a deal finalized on May 11, 2009, with Rackable assuming the name Silicon Graphics International; the remains of Silicon Graphics, Inc. became Graphics Properties Holdings, Inc. James H. Clark left his position as an electrical engineering associate professor at Stanford University to found SGI in 1982 along with a group of seven graduate students and research staff from Stanford: Kurt Akeley, David J. Brown, Tom Davis, Rocky Rhodes, Marc Hannah, Herb Kuta, Mark Grossman.
Ed McCracken was CEO of Silicon Graphics from 1984 to 1997. During those years, SGI grew from annual revenues of $5.4 million to $3.7 billion. The addition of 3D graphic capabilities to PCs, the ability of clusters of Linux- and BSD-based PCs to take on many of the tasks of larger SGI servers, ate into SGI's core markets; the porting of Maya to Linux, Mac OS X and Microsoft Windows further eroded the low end of SGI's product line. In response to challenges faced in the marketplace and a falling share price Ed McCracken was fired and SGI brought in Richard Belluzzo to replace him. Under Belluzzo's leadership a number of initiatives were taken which are considered to have accelerated the corporate decline. One such initiative was trying to sell workstations running Windows NT called Visual Workstations instead of just ones which ran IRIX, the company's version of UNIX; this put the company in more direct competition with the likes of Dell, making it more difficult to justify a price premium. The product line abandoned a few years later.
SGI's premature announcement of its migration from MIPS to Itanium and its abortive ventures into IA-32 architecture systems damaged SGI's credibility in the market. In 1999, in an attempt to clarify their current market position as more than a graphics company, Silicon Graphics Inc. changed its corporate identity to "SGI", although its legal name was unchanged. At the same time, SGI announced a new logo consisting of only the letters "sgi" in a proprietary font called "SGI", created by branding and design consulting firm Landor Associates, in collaboration with designer Joe Stitzlein. SGI continued to use the "Silicon Graphics" name for its workstation product line, re-adopted the cube logo for some workstation models. In November 2005, SGI announced that it had been delisted from the New York Stock Exchange because its common stock had fallen below the minimum share price for listing on the exchange. SGI's market capitalization dwindled from a peak of over seven billion dollars in 1995 to just $120 million at the time of delisting.
In February 2006, SGI noted. In mid-2005, SGI hired Alix Partners to advise it on returning to profitability and received a new line of credit. SGI announced it was postponing its scheduled annual December stockholders meeting until March 2006, it proposed a reverse stock split to deal with the de-listing from the New York Stock Exchange. In January 2006, SGI hired Dennis McKenna as its new chairman of the board of directors. Mr. McKenna succeeded Robert Bishop. On May 8, 2006, SGI announced that it had filed for Chapter 11 bankruptcy protection for itself and U. S. subsidiaries as part of a plan to reduce debt by $250 million. Two days the U. S. Bankruptcy Court approved its first day motions and its use of a $70 million financing facility provided by a group of its bondholders. Foreign subsidiaries were unaffected. On September 6, 2006, SGI announced the end of development for the MIPS/IRIX line and the IRIX operating system. Production would end on December 29 and the last orders would be fulfilled by March 2007.
Support for these products would end after December 2013. SGI emerged from bankruptcy protection on October 17, 2006, its stock symbol at that point, SGID.pk, was canceled, new stock was issued on the NASDAQ exchange under the symbol SGIC. This new stock was distributed to the company's creditors, the SGID common stockh
Unix is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, development starting in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, others. Intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Microsoft, IBM, Sun Microsystems. In the early 1990s, AT&T sold its rights in Unix to Novell, which sold its Unix business to the Santa Cruz Operation in 1995; the UNIX trademark passed to The Open Group, a neutral industry consortium, which allows the use of the mark for certified operating systems that comply with the Single UNIX Specification. As of 2014, the Unix version with the largest installed base is Apple's macOS. Unix systems are characterized by a modular design, sometimes called the "Unix philosophy"; this concept entails that the operating system provides a set of simple tools that each performs a limited, well-defined function, with a unified filesystem as the main means of communication, a shell scripting and command language to combine the tools to perform complex workflows.
Unix distinguishes itself from its predecessors as the first portable operating system: the entire operating system is written in the C programming language, thus allowing Unix to reach numerous platforms. Unix was meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmers; the system grew larger as the operating system started spreading in academic circles, as users added their own tools to the system and shared them with colleagues. At first, Unix was not designed to be multi-tasking. Unix gained portability, multi-tasking and multi-user capabilities in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; these concepts are collectively known as the "Unix philosophy". Brian Kernighan and Rob Pike summarize this in The Unix Programming Environment as "the idea that the power of a system comes more from the relationships among programs than from the programs themselves".
In an era when a standard computer consisted of a hard disk for storage and a data terminal for input and output, the Unix file model worked quite well, as I/O was linear. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, semaphores, network sockets were added to support communication with other hosts; as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. By the early 1980s, users began seeing Unix as a potential universal operating system, suitable for computers of all sizes; the Unix environment and the client–server program model were essential elements in the development of the Internet and the reshaping of computing as centered in networks rather than in individual computers. Both Unix and the C programming language were developed by AT&T and distributed to government and academic institutions, which led to both being ported to a wider variety of machine families than any other operating system.
Under Unix, the operating system consists of many libraries and utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handles the file system and other common "low-level" tasks that most programs share, schedules access to avoid conflicts when programs try to access the same resource or device simultaneously. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space - although in microkernel implementations, like MINIX or Redox, functions such as network protocols may run in user space; the origins of Unix date back to the mid-1960s when the Massachusetts Institute of Technology, Bell Labs, General Electric were developing Multics, a time-sharing operating system for the GE-645 mainframe computer. Multics featured several innovations, but presented severe problems. Frustrated by the size and complexity of Multics, but not by its goals, individual researchers at Bell Labs started withdrawing from the project.
The last to leave were Ken Thompson, Dennis Ritchie, Douglas McIlroy, Joe Ossanna, who decided to reimplement their experiences in a new project of smaller scale. This new operating system was without organizational backing, without a name; the new operating system was a single-tasking system. In 1970, the group coined the name Unics for Uniplexed Information and Computing Service, as a pun on Multics, which stood for Multiplexed Information and Computer Services. Brian Kernighan takes credit for the idea, but adds that "no one can remember" the origin of the final spelling Unix. Dennis Ritchie, Doug McIlroy, Peter G. Neumann credit Kernighan; the operating system was written in assembly language, but in 1973, Version 4 Unix was rewritten in C. Version 4 Unix, still had many PDP-11 dependent codes, is not suitable for porting; the first port to other platform was made five years f
X86-64 is the 64-bit version of the x86 instruction set. It introduces two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode. With 64-bit mode and the new paging mode, it supports vastly larger amounts of virtual memory and physical memory than is possible on its 32-bit predecessors, allowing programs to store larger amounts of data in memory. X86-64 expands general-purpose registers to 64-bit, as well extends the number of them from 8 to 16, provides numerous other enhancements. Floating point operations are supported via mandatory SSE2-like instructions, x87/MMX style registers are not used. In 64-bit mode, instructions are modified to support 64-bit addressing mode; the compatibility mode allows 16- and 32-bit user applications to run unmodified coexisting with 64-bit applications if the 64-bit operating system supports them. As the full x86 16-bit and 32-bit instruction sets remain implemented in hardware without any intervening emulation, these older executables can run with little or no performance penalty, while newer or modified applications can take advantage of new features of the processor design to achieve performance improvements.
A processor supporting x86-64 still powers on in real mode for full backward compatibility. The original specification, created by AMD and released in 2000, has been implemented by AMD, Intel and VIA; the AMD K8 processor was the first to implement it. This was the first significant addition to the x86 architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified NetBurst family, software-compatible with AMD's specification. VIA Technologies introduced x86-64 with the VIA Nano; the x86-64 architecture is distinct from the Intel Itanium architecture, not compatible on the native instruction set level with the x86 architecture. Operating systems and applications written for one cannot be run on the other. AMD64 was created as an alternative to the radically different IA-64 architecture, designed by Intel and Hewlett Packard. Announced in 1999 while a full specification became available in August 2000, the AMD64 architecture was positioned by AMD from the beginning as an evolutionary way to add 64-bit computing capabilities to the existing x86 architecture, as opposed to Intel's approach of creating an new 64-bit architecture with IA-64.
The first AMD64-based processor, the Opteron, was released in April 2003. AMD's processors implementing the AMD64 architecture include Opteron, Athlon 64, Athlon 64 X2, Athlon 64 FX, Athlon II, Turion 64, Turion 64 X2, Phenom, Phenom II, FX, Fusion/APU and Ryzen/Epyc; the primary defining characteristic of AMD64 is the availability of 64-bit general-purpose processor registers, 64-bit integer arithmetic and logical operations, 64-bit virtual addresses. The designers took the opportunity to make other improvements as well; some of the most significant changes are described below. 64-bit integer capability All general-purpose registers are expanded from 32 bits to 64 bits, all arithmetic and logical operations, memory-to-register and register-to-memory operations, etc. can now operate directly on 64-bit integers. Pushes and pops on the stack default to 8-byte strides, pointers are 8 bytes wide. Additional registers In addition to increasing the size of the general-purpose registers, the number of named general-purpose registers is increased from eight in x86 to 16.
It is therefore possible to keep more local variables in registers rather than on the stack, to let registers hold accessed constants. AMD64 still has fewer registers than many RISC instruction sets or VLIW-like machines such as the IA-64. However, an AMD64 implementation may have far more internal registers than the number of architectural registers exposed by the instruction set. Additional XMM registers Similarly, the number of 128-bit XMM registers is increased from 8 to 16; the traditional x87 FPU register stack is not included in the register file size extension in 64-bit mode, compared with the XMM registers used by SSE2, which did get extended. The x87 register stack is not a simple register file although it does allow direct access to individual registers by low cost exchange operations. Larger virtual address space The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations; this allows up to 256 TB of virtual address space.
The architecture definition allows this limit to be raised in future implementations to the full 64 bits, exten