University of Melbourne
The University of Melbourne is a public research university located in Melbourne, Australia. Founded in 1853, it is the oldest in Victoria. Melbourne's main campus is located in Parkville, an inner suburb north of the Melbourne central business district, with several other campuses located across Victoria. Melbourne is a sandstone university and a member of the Group of Eight, Universitas 21 and the Association of Pacific Rim Universities. Since 1872 various residential colleges have become affiliated with the university. There are 10 colleges located on the main campus and in nearby suburbs offering academic and cultural programs alongside accommodation for Melbourne students and faculty. Melbourne comprises 11 separate academic units and is associated with numerous institutes and research centres, including the Walter and Eliza Hall Institute of Medical Research, Florey Institute of Neuroscience and Mental Health, the Melbourne Institute of Applied Economic and Social Research and the Grattan Institute.
Amongst Melbourne's 15 graduate schools the Melbourne Business School, the Melbourne Law School and the Melbourne Medical School are well regarded. Times Higher Education ranked Melbourne 32nd globally in 2017-2018, while the Academic Ranking of World Universities places Melbourne 38th in the world, in the QS World University Rankings 2019 Melbourne ranks 39th globally and ranked sixth in the world according to the 2019 QS Graduate Employability Rankings. Four Australian prime ministers and five governors-general have graduated from the University of Melbourne. Ten Nobel laureates have been the most of any Australian university; the University of Melbourne was established by Hugh Childers, the Auditor-General and Finance Minister, in his first Budget Speech on 4 November 1852, who set aside a sum of £10,000 for the establishment of a university. The university was established by Act of Incorporation on 22 January 1853, with power to confer degrees in arts, medicine and music; the act provided for an annual endowment of £9,000, while a special grant of £20,000 was made for buildings that year.
The foundation stone was laid on 3 July 1854, on the same day the foundation stone for the State Library Classes commenced in 1855 with three professors and sixteen students. The original buildings were opened by the Lieutenant Governor of the Colony of Victoria, Sir Charles Hotham, on 3 October 1855; the first chancellor, Redmond Barry, held the position until his death in 1880. The inauguration of the university was made possible by the wealth resulting from Victoria's gold rush; the institution was designed to be a "civilising influence" at a time of rapid settlement and commercial growth. In 1881, the admission of women was a seen as victory over the more conservative ruling council; the university's 150th anniversary was celebrated in 2003. The Melbourne School of Land and Environment was disestablished on the first of January, 2015, its agriculture and food systems department moved alongside veterinary science to form the Faculty of Veterinary and Agricultural Sciences, while other areas of study, including horticulture, forestry and resource management, moved to the Faculty of Science in two new departments.
As of May 2009 the university "suspended" the Bachelor of Music Theatre and Puppetry courses at the college and there were fears they may not return under the new curriculum. A 2005 heads of agreement over the merger of the VCA and the university stated that the management of academic programs at the VCA would ensure that "the VCA continues to exercise high levels of autonomy over the conduct and future development of its academic programs so as to ensure their integrity and quality" and that the college's identity will be preserved. New dean Sharman Pretty outlined drastic changes under the university's plan for the college in early April 2009; as a result, it is now being called into question. Staff at the college responded to the changes, claiming the university did not value vocational arts training, voicing fears over the future of quality training at the VCA. Former Victorian arts minister Race Mathews has weighed in on the debate expressing his hope that, "Melbourne University will not proceed with its proposed changes to the Victorian College of the Arts", for'good sense' to prevail.
In 2011, the Victorian State Government allocated $24 million to support arts education at the VCA and the faculty was renamed the Faculty of the Victorian College of the Arts and the Melbourne Conservatorium of Music. The Parkville Campus is the primary campus of the university. Established in a large area north of Grattan Street in Parkville, the campus has expanded well beyond its boundaries, with many of its newly acquired buildings located in the nearby suburb of Carlton; the university is undertaking an'ambitious infrastructure program' to reshape campuses. Melbourne University has 10 residential colleges in total, seven of which are located in an arc around the cricket oval at the northern edge of the campus, known as College Crescent; the other three are located outside of university grounds. The residential colleges aim to provide accommodation and holistic education experience to university students. Most of the university's residential colleges admit students from RMIT University and Monash University, Parkville campus, with selected colleges accepting students from the Australian Catholic University and Victoria University.
Several of the earliest campus buildings, such as the Old Quadrangle and Baldwin Spencer buildings, feature period architecture. The new Wilson Hall replaced th
Android (operating system)
Android is a mobile operating system developed by Google. It is based on a modified version of the Linux kernel and other open source software, is designed for touchscreen mobile devices such as smartphones and tablets. In addition, Google has further developed Android TV for televisions, Android Auto for cars, Wear OS for wrist watches, each with a specialized user interface. Variants of Android are used on game consoles, digital cameras, PCs and other electronics. Developed by Android Inc. which Google bought in 2005, Android was unveiled in 2007, with the first commercial Android device launched in September 2008. The operating system has since gone through multiple major releases, with the current version being 9 "Pie", released in August 2018. Google released the first Android Q beta on all Pixel phones on March 13, 2019; the core Android source code is known as Android Open Source Project, is licensed under the Apache License. Android is associated with a suite of proprietary software developed by Google, called Google Mobile Services that frequently comes pre-installed in devices, which includes the Google Chrome web browser and Google Search and always includes core apps for services such as Gmail, as well as the application store and digital distribution platform Google Play, associated development platform.
These apps are licensed by manufacturers of Android devices certified under standards imposed by Google, but AOSP has been used as the basis of competing Android ecosystems, such as Amazon.com's Fire OS, which use their own equivalents to GMS. Android has been the best-selling OS worldwide on smartphones since 2011 and on tablets since 2013; as of May 2017, it has over two billion monthly active users, the largest installed base of any operating system, as of December 2018, the Google Play store features over 2.6 million apps. The name Andrew and the noun Android share the Greek root andros. Andy Rubin picked android.com as his personal website, his colleagues used Android as his nickname at work. That became the name of the company he founded, the name of the operating system they developed. Android Inc. was founded in Palo Alto, California, in October 2003 by Andy Rubin, Rich Miner, Nick Sears, Chris White. Rubin described the Android project as "tremendous potential in developing smarter mobile devices that are more aware of its owner's location and preferences".
The early intentions of the company were to develop an advanced operating system for digital cameras, this was the basis of its pitch to investors in April 2004. The company decided that the market for cameras was not large enough for its goals, by five months it had diverted its efforts and was pitching Android as a handset operating system that would rival Symbian and Microsoft Windows Mobile. Rubin had difficulty attracting investors early on, Android was facing eviction from its office space. Steve Perlman, a close friend of Rubin, brought him $10,000 in cash in an envelope, shortly thereafter wired an undisclosed amount as seed funding. Perlman refused a stake in the company, has stated "I did it because I believed in the thing, I wanted to help Andy."In July 2005, Google acquired Android Inc. for at least $50 million. Its key employees, including Rubin and White, joined Google as part of the acquisition. Not much was known about the secretive Android at the time, with the company having provided few details other than that it was making software for mobile phones.
At Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel. Google marketed the platform to handset makers and carriers on the promise of providing a flexible, upgradeable system. Google had "lined up a series of hardware components and software partners and signaled to carriers that it was open to various degrees of cooperation". Speculation about Google's intention to enter the mobile communications market continued to build through December 2006. An early prototype had a close resemblance to a BlackBerry phone, with no touchscreen and a physical QWERTY keyboard, but the arrival of 2007's Apple iPhone meant that Android "had to go back to the drawing board". Google changed its Android specification documents to state that "Touchscreens will be supported", although "the Product was designed with the presence of discrete physical buttons as an assumption, therefore a touchscreen cannot replace physical buttons". By 2008, both Nokia and BlackBerry announced touch-based smartphones to rival the iPhone 3G, Android's focus switched to just touchscreens.
The first commercially available smartphone running Android was the HTC Dream known as T-Mobile G1, announced on September 23, 2008. On November 5, 2007, the Open Handset Alliance, a consortium of technology companies including Google, device manufacturers such as HTC, Motorola and Samsung, wireless carriers such as Sprint and T-Mobile, chipset makers such as Qualcomm and Texas Instruments, unveiled itself, with a goal to develop "the first open and comprehensive platform for mobile devices". Within a year, the Open Handset Alliance faced two other open source competitors, the Symbian Foundation and the LiMo Foundation, the latter developing a Linux-based mobile operating system like Google. In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony. Since 2008, Android has seen numerous updates which have incrementally improved the operating system, adding new features and fixing bugs in previous releases.
Each major release is named in alphabetical order after a dessert or sugary treat, with the first few Android versions being called "Cupcake", "Donut"
An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, use in 2017 is up to 70% of Google's Android and according to third quarter 2016 data, Android on smartphones is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by Apple's iOS with 12.1 percent and a per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.
Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking.
32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer; the development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system.
In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.
A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries and parallel processing; when personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems.
Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the pri
Mercurial is a distributed revision-control tool for software developers. It is supported on Unix-like systems, such as FreeBSD, macOS and Linux. Mercurial's major design goals include high performance and scalability, decentralization distributed collaborative development, robust handling of both plain text and binary files, advanced branching and merging capabilities, while remaining conceptually simple, it includes an integrated web-interface. Mercurial has taken steps to ease the transition for users of other version control systems Subversion. Mercurial is a command-line driven program, but graphical user interface extensions are available, e.g. TortoiseHg, several IDEs offer support for version control with Mercurial. All of Mercurial's operations are invoked as arguments to its driver program hg. Matt Mackall originated Mercurial and has served as its lead developer until late 2016. Mercurial is released as free software under the terms of the GNU GPL v2, it is implemented using the Python programming language, but includes a binary diff implementation written in C.
Mackall first announced Mercurial on 19 April 2005. The impetus for this was the announcement earlier that month by Bitmover that they were withdrawing the free version of BitKeeper. BitKeeper had been used for the version control requirements of the Linux kernel project. Mackall decided to write a distributed version control system as a replacement for use with the Linux kernel; this project started a few days after the now well-known Git project was initiated by Linus Torvalds with similar aims. The Linux kernel project decided to use Git rather than Mercurial, but Mercurial is now used by many other projects. "Git vs. Mercurial" has become one of the holy wars of hacker culture. In an answer on the Mercurial mailing list, Matt Mackall explained how the name "Mercurial" was chosen: In 2013, Facebook adopted Mercurial and began work on scaling it to handle their large, unified code repository. Mercurial uses SHA-1 hashes to identify revisions. For repository access via a network, Mercurial uses an HTTP-based protocol that seeks to reduce round-trip requests, new connections and data transferred.
Mercurial can work over SSH where the protocol is similar to the HTTP-based protocol. By default it uses a 3-way merge before calling external merge tools. Figure 1 shows some of the most important operations in Mercurial and their relations to Mercurial's concepts. Although Mercurial was not selected to manage the Linux kernel sources, it has been adopted by several organizations, including Facebook, the W3C, Mozilla. Facebook is using the Rust programming language to write Mononoke, a Mercurial server designed to support large multi-project repositories. RhodeCode by RhodeCode Inc. Kallithea, a GPLv3 fork of RhodeCode Kiln by Fog Creek Software The following websites provide free source code hosting for Mercurial repositories: Bitbucket by Atlassian Codebase SourceForge GNU Savannah by FSF Puszcza OSDN Perforce Mozdev TuxFamily FusionForge Others Some projects using the Mercurial distributed RCS: Distributed version control List of version control software Comparison of version control software Official website O'Sullivan, Mercurial: The Definitive Guide, O'Reilly available online "Mercurial: an alternative to git", LWN An example-based Mercurial tutorial, SE: Jemander covering both basic and advanced use "Mercurial", TechTalk, Google "Subversion or CVS, Bazaar or Mercurial?
Four open source version control systems compared", Java World, Sep 2007 Spolsky, Mercurial tutorial Mackall, Matt, "FLOSS Podcast", This week in Tech List of projects using Mercurial from the Mercurial wiki
Microsoft Windows is a group of several graphical operating system families, all of which are developed and sold by Microsoft. Each family caters to a certain sector of the computing industry. Active Windows families include Windows Embedded. Defunct Windows families include Windows Mobile and Windows Phone. Microsoft introduced an operating environment named Windows on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces. Microsoft Windows came to dominate the world's personal computer market with over 90% market share, overtaking Mac OS, introduced in 1984. Apple came to see Windows as an unfair encroachment on their innovation in GUI development as implemented on products such as the Lisa and Macintosh. On PCs, Windows is still the most popular operating system. However, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones.
In 2014, the number of Windows devices sold was less than 25 %. This comparison however may not be relevant, as the two operating systems traditionally target different platforms. Still, numbers for server use of Windows show one third market share, similar to that for end user use; as of October 2018, the most recent version of Windows for PCs, tablets and embedded devices is Windows 10. The most recent versions for server computers is Windows Server 2019. A specialized version of Windows runs on the Xbox One video game console. Microsoft, the developer of Windows, has registered several trademarks, each of which denote a family of Windows operating systems that target a specific sector of the computing industry; as of 2014, the following Windows families are being developed: Windows NT: Started as a family of operating systems with Windows NT 3.1, an operating system for server computers and workstations. It now consists of three operating system subfamilies that are released at the same time and share the same kernel: Windows: The operating system for mainstream personal computers and smartphones.
The latest version is Windows 10. The main competitor of this family is macOS by Apple for personal computers and Android for mobile devices. Windows Server: The operating system for server computers; the latest version is Windows Server 2019. Unlike its client sibling, it has adopted a strong naming scheme; the main competitor of this family is Linux. Windows PE: A lightweight version of its Windows sibling, meant to operate as a live operating system, used for installing Windows on bare-metal computers, recovery or troubleshooting purposes; the latest version is Windows PE 10. Windows IoT: Initially, Microsoft developed Windows CE as a general-purpose operating system for every device, too resource-limited to be called a full-fledged computer. However, Windows CE was renamed Windows Embedded Compact and was folded under Windows Compact trademark which consists of Windows Embedded Industry, Windows Embedded Professional, Windows Embedded Standard, Windows Embedded Handheld and Windows Embedded Automotive.
The following Windows families are no longer being developed: Windows 9x: An operating system that targeted consumers market. Discontinued because of suboptimal performance. Microsoft now caters to the consumer market with Windows NT. Windows Mobile: The predecessor to Windows Phone, it was a mobile phone operating system; the first version was called Pocket PC 2000. The last version is Windows Mobile 6.5. Windows Phone: An operating system sold only to manufacturers of smartphones; the first version was Windows Phone 7, followed by Windows Phone 8, the last version Windows Phone 8.1. It was succeeded by Windows 10 Mobile; the term Windows collectively describes any or all of several generations of Microsoft operating system products. These products are categorized as follows: The history of Windows dates back to 1981, when Microsoft started work on a program called "Interface Manager", it was announced in November 1983 under the name "Windows", but Windows 1.0 was not released until November 1985.
Windows 1.0 was to achieved little popularity. Windows 1.0 is not a complete operating system. The shell of Windows 1.0 is a program known as the MS-DOS Executive. Components included Calculator, Cardfile, Clipboard viewer, Control Panel, Paint, Reversi and Write. Windows 1.0 does not allow overlapping windows. Instead all windows are tiled. Only modal dialog boxes may appear over other windows. Microsoft sold as included Windows Development libraries with the C development environment, which included numerous windows samples. Windows 2.0 was released in December 1987, was more popular than its predecessor. It features several improvements to the user memory management. Windows 2.03 changed the OS from tiled windows to overlapping windows. The result of this change led to Apple Computer filing a suit against Microsoft alleging infringement on Apple's copyrights. Windows 2.0
ARM Advanced RISC Machine Acorn RISC Machine, is a family of reduced instruction set computing architectures for computer processors, configured for various environments. Arm Holdings develops the architecture and licenses it to other companies, who design their own products that implement one of those architectures—including systems-on-chips and systems-on-modules that incorporate memory, radios, etc, it designs cores that implement this instruction set and licenses these designs to a number of companies that incorporate those core designs into their own products. Processors that have a RISC architecture require fewer transistors than those with a complex instruction set computing architecture, which improves cost, power consumption, heat dissipation; these characteristics are desirable for light, battery-powered devices—including smartphones and tablet computers, other embedded systems. For supercomputers, which consume large amounts of electricity, ARM could be a power-efficient solution.
ARM Holdings periodically releases updates to the architecture. Architecture versions ARMv3 to ARMv7 support 32-bit arithmetic; the Thumb version supports a variable-length instruction set that provides both 32- and 16-bit instructions for improved code density. Some older cores can provide hardware execution of Java bytecodes. Released in 2011, the ARMv8-A architecture added support for a 64-bit address space and 64-bit arithmetic with its new 32-bit fixed-length instruction set. With over 100 billion ARM processors produced as of 2017, ARM is the most used instruction set architecture and the instruction set architecture produced in the largest quantity; the used Cortex cores, older "classic" cores, specialized SecurCore cores variants are available for each of these to include or exclude optional capabilities. The British computer manufacturer Acorn Computers first developed the Acorn RISC Machine architecture in the 1980s to use in its personal computers, its first ARM-based products were coprocessor modules for the BBC Micro series of computers.
After the successful BBC Micro computer, Acorn Computers considered how to move on from the simple MOS Technology 6502 processor to address business markets like the one, soon dominated by the IBM PC, launched in 1981. The Acorn Business Computer plan required that a number of second processors be made to work with the BBC Micro platform, but processors such as the Motorola 68000 and National Semiconductor 32016 were considered unsuitable, the 6502 was not powerful enough for a graphics-based user interface. According to Sophie Wilson, all the processors tested at that time performed about the same, with about a 4 Mbit/second bandwidth. After testing all available processors and finding them lacking, Acorn decided it needed a new architecture. Inspired by papers from the Berkeley RISC project, Acorn considered designing its own processor. A visit to the Western Design Center in Phoenix, where the 6502 was being updated by what was a single-person company, showed Acorn engineers Steve Furber and Sophie Wilson they did not need massive resources and state-of-the-art research and development facilities.
Wilson developed the instruction set, writing a simulation of the processor in BBC BASIC that ran on a BBC Micro with a 6502 second processor. This convinced Acorn engineers. Wilson approached Acorn's CEO, Hermann Hauser, requested more resources. Hauser assembled a small team to implement Wilson's model in hardware; the official Acorn RISC Machine project started in October 1983. They chose VLSI Technology as the silicon partner, as they were a source of ROMs and custom chips for Acorn. Wilson and Furber led the design, they implemented it with a similar efficiency ethos as the 6502. A key design goal was achieving low-latency input/output handling like the 6502; the 6502's memory access architecture had let developers produce fast machines without costly direct memory access hardware. The first samples of ARM silicon worked properly when first received and tested on 26 April 1985; the first ARM application was as a second processor for the BBC Micro, where it helped in developing simulation software to finish development of the support chips, sped up the CAD software used in ARM2 development.
Wilson subsequently rewrote BBC BASIC in ARM assembly language. The in-depth knowledge gained from designing the instruction set enabled the code to be dense, making ARM BBC BASIC an good test for any ARM emulator; the original aim of a principally ARM-based computer was achieved in 1987 with the release of the Acorn Archimedes. In 1992, Acorn once more won the Queen's Award for Technology for the ARM; the ARM2 featured 26-bit address space and 27 32-bit registers. Eight bits from the program counter register were available for other purposes; the address bus was extended to 32 bits in the ARM6, but program code still had to lie within the first 64 MB of memory in 26-bit compatibility mode, due to the reserved bits for the status flags. The ARM2 had a transistor count of just 30,000, compared to Motorola's six-year-older 68000 model with around 40,000. Much of this simplicity came from the lack of mic
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