1.
Central processing unit
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The computer industry has used the term central processing unit at least since the early 1960s. The form, design and implementation of CPUs have changed over the course of their history, most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may also contain memory, peripheral interfaces, some computers employ a multi-core processor, which is a single chip containing two or more CPUs called cores, in that context, one can speak of such single chips as sockets. Array processors or vector processors have multiple processors that operate in parallel, there also exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be rewired to perform different tasks. Since the term CPU is generally defined as a device for software execution, the idea of a stored-program computer was already present in the design of J. Presper Eckert and John William Mauchlys ENIAC, but was initially omitted so that it could be finished sooner. On June 30,1945, before ENIAC was made, mathematician John von Neumann distributed the paper entitled First Draft of a Report on the EDVAC and it was the outline of a stored-program computer that would eventually be completed in August 1949. EDVAC was designed to perform a number of instructions of various types. Significantly, the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the wiring of the computer. This overcame a severe limitation of ENIAC, which was the considerable time, with von Neumanns design, the program that EDVAC ran could be changed simply by changing the contents of the memory. Early CPUs were custom designs used as part of a larger, however, this method of designing custom CPUs for a particular application has largely given way to the development of multi-purpose processors produced in large quantities. This standardization began in the era of discrete transistor mainframes and minicomputers and has accelerated with the popularization of the integrated circuit. The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers, both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles to cellphones, the so-called Harvard architecture of the Harvard Mark I, which was completed before EDVAC, also utilized a stored-program design using punched paper tape rather than electronic memory. Relays and vacuum tubes were used as switching elements, a useful computer requires thousands or tens of thousands of switching devices. The overall speed of a system is dependent on the speed of the switches, tube computers like EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed very rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems, most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were very common at this time, the design complexity of CPUs increased as various technologies facilitated building smaller and more reliable electronic devices
2.
Computer data storage
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Computer data storage, often called storage or memory, is a technology consisting of computer components and recording media used to retain digital data. It is a function and fundamental component of computers. The central processing unit of a computer is what manipulates data by performing computations, in practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but larger and cheaper options farther away. In the Von Neumann architecture, the CPU consists of two parts, The control unit and the arithmetic logic unit. The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data, without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior and this is acceptable for devices such as desk calculators, digital signal processors, and other specialized devices. Von Neumann machines differ in having a memory in which they store their operating instructions, most modern computers are von Neumann machines. A modern digital computer represents data using the numeral system. Text, numbers, pictures, audio, and nearly any form of information can be converted into a string of bits, or binary digits. The most common unit of storage is the byte, equal to 8 bits, a piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, the works of Shakespeare, about 1250 pages in print. Data is encoded by assigning a bit pattern to each character, digit, by adding bits to each encoded unit, redundancy allows the computer to both detect errors in coded data and correct them based on mathematical algorithms. A random bit flip is typically corrected upon detection, the cyclic redundancy check method is typically used in communications and storage for error detection. A detected error is then retried, data compression methods allow in many cases to represent a string of bits by a shorter bit string and reconstruct the original string when needed. This utilizes substantially less storage for many types of data at the cost of more computation, analysis of trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not. For security reasons certain types of data may be encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots. Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and this traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit. In contemporary usage, memory is usually semiconductor storage read-write random-access memory, typically DRAM or other forms of fast but temporary storage
3.
Parallel computing
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Parallel computing is a type of computation in which many calculations or the execution of processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time, there are several different forms of parallel computing, bit-level, instruction-level, data, and task parallelism. Parallelism has been employed for years, mainly in high-performance computing. As power consumption by computers has become a concern in recent years, parallel computing has become the dominant paradigm in computer architecture, specialized parallel computer architectures are sometimes used alongside traditional processors, for accelerating specific tasks. Communication and synchronization between the different subtasks are typically some of the greatest obstacles to getting good parallel program performance, a theoretical upper bound on the speed-up of a single program as a result of parallelization is given by Amdahls law. Traditionally, computer software has been written for serial computation, to solve a problem, an algorithm is constructed and implemented as a serial stream of instructions. These instructions are executed on a central processing unit on one computer, only one instruction may execute at a time—after that instruction is finished, the next one is executed. Parallel computing, on the hand, uses multiple processing elements simultaneously to solve a problem. This is accomplished by breaking the problem into independent parts so that each processing element can execute its part of the algorithm simultaneously with the others. The processing elements can be diverse and include such as a single computer with multiple processors, several networked computers, specialized hardware. Frequency scaling was the dominant reason for improvements in performance from the mid-1980s until 2004. The runtime of a program is equal to the number of instructions multiplied by the time per instruction. Maintaining everything else constant, increasing the frequency decreases the average time it takes to execute an instruction. An increase in frequency thus decreases runtime for all compute-bound programs. However, power consumption P by a chip is given by the equation P = C × V2 × F, where C is the capacitance being switched per clock cycle, V is voltage, increases in frequency increase the amount of power used in a processor. Moores law is the observation that the number of transistors in a microprocessor doubles every 18 to 24 months. Despite power consumption issues, and repeated predictions of its end, with the end of frequency scaling, these additional transistors can be used to add extra hardware for parallel computing. Optimally, the speedup from parallelization would be linear—doubling the number of processing elements should halve the runtime, however, very few parallel algorithms achieve optimal speedup
4.
J. Lyons and Co.
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J. Lyons & Co. was a market dominant British restaurant chain, food manufacturing, and hotel conglomerate founded in 1884. The company began as collaboration between the professional artist Joseph Lyons and his brothers in law, Isidore and Montague Gluckstein, in 1894 the company started a teashop in Piccadilly, London, and from 1909 developed this into a chain of teashops known as Lyons Corner Houses. From the 1930s Lyons began to develop a range of teas, biscuits. Lyons, who founded the UKs Territorial Force, now known as the Army Reserve, was appointed to run the company. J. Lyons & Co. was a pioneer in introducing computers to business, between 1951 and 1963, the company manufactured and sold a range of LEO computers. The company was a food manufacturer, with factories at Cadby Hall in Hammersmith. To the public, J. Lyons & Co. were best known for their chain of tea shops which opened from 1894 and finally closed in 1981, the tea shops were slightly more up market than their ABC counterparts. They were notable for their design, from the 1920s Oliver P. Until the 1940s they had a certain chic, but by the 1950s and 60s they were quick stops for busy shoppers where one could drink a cup of tea. The tea shops always had a counter at the front. The Corner Houses, which first appeared in 1909 and remained until 1977, were noted for their art deco style, in addition, they possessed hairdressing salons, telephone booths, theatre booking agencies and at one period a twice-a-day food delivery service. On the other floors were several restaurants, each with a different theme, for a time the Corner Houses were open 24 hours a day, and at their peak each branch employed around 400 staff. They featured window displays designed by Kay Lipton and, in the post-war period, between 1896 and 1965 Lyons owned the Trocadero, which was similar in size and style to the Corner Houses. As well as the tea shops and Corner Houses, Lyons ran other large restaurants such as the Angel Cafe Restaurant in Islington and its chains have included Steak Houses, Wimpy Bars, Baskin-Robbins and Dunkin Donuts. The artist Kay Lipton designed all the windows for the Corner Houses under the jurisdiction of Mr. Norman Joseph the Director post-war. The Regent Palace Hotel, Glasshouse Street, London was operated by Strand Hotels Limited, Strand Hotels also operated the Cumberland Hotel, Kingsley Hotel, Park Court Hotel, Windsor Hotel, Whites Hotel and the Strand Palace Hotel after the inception of Strand Hotels Limited. The last London hotel that operated until the demise of the group in the mid-70s was the Tower Hotel situated by Tower Bridge in London. In 1938, Lyons purchased the Bee Bee Biscuit Company, which manufactured biscuits from its factories in Blackpool
5.
Unix
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Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. 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, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers
6.
PDP-8
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The 12-bit PDP-8, produced by Digital Equipment Corporation, was the first successful commercial minicomputer. DEC introduced it on March 22,1965 priced at $18,500 and eventually more than 50,000 systems. The PDP-8 was the first computer to be sold for under $20,000 and it was the first widely sold computer in the DEC PDP series of computers. The chief engineer who designed the initial version of the PDP-8 was Edson de Castro, the earliest PDP-8 model uses diode–transistor logic, packaged on flip chip cards, and is about the size of a small household refrigerator. This was followed in 1966 by the PDP-8/S, available in desktop, using a one-bit serial arithmetic logic unit implementation, allowed the PDP-8/S to be smaller, less expensive and slower than the original PDP-8. The PDP-8/S was about 20% of the cost and about 10% of the performance of the PDP-8, the only mass storage peripheral available for the PDP-8/S was the DF32 disk. Later systems returned to a faster, fully parallel implementation but use less costly transistor-transistor logic MSI logic. Most surviving PDP-8s are from this era, the PDP-8/E is common, and well-regarded because so many types of I/O devices were available for it. It was often configured as a general-purpose computer, the last commercial PDP-8 models introduced in 1979 were called CMOS-8s. They use custom complementary metal-oxide-semiconductor microprocessors and they were not priced competitively, and the offering failed. The IBM PC in 1981 cemented the doom of the CMOS-8s by making a legitimate, Intersil sold the integrated circuits commercially through to 1982 as the Intersil 6100 family. By virtue of their CMOS technology they had low power requirements and were used in some embedded military systems, the PDP-8 combined low cost, simplicity, expandability, and careful engineering for value. The greatest historical significance was that the PDP-8s low cost and high volume made a computer available to new people for many new uses. Its continuing significance is as a example of value-engineered computer design. The low complexity brought other costs and it made programming cumbersome, as is seen in the examples in this article and from the discussion of pages and fields. Some ambitious programming projects failed to fit in memory or developed design defects that could not be solved, as design advances reduced the costs of logic and memory, the programmers time became relatively more important. Subsequent computer designs emphasized ease of programming, typically using a larger, eventually, most machine-language programming came to be generated by compilers and report generators. The PDP-8 used ideas from several 12-bit predecessors, most notably the LINC designed by W. A. Clark, the architecture has a simple programmed I/O bus, plus a DMA channel
7.
Linux
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Linux is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. The defining component of Linux is the Linux kernel, an operating system kernel first released on September 17,1991 by Linus Torvalds, the Free Software Foundation uses the name GNU/Linux to describe the operating system, which has led to some controversy. Linux was originally developed for computers based on the Intel x86 architecture. Because of the dominance of Android on smartphones, Linux has the largest installed base of all operating systems. Linux is also the operating system on servers and other big iron systems such as mainframe computers. It is used by around 2. 3% of desktop computers, the Chromebook, which runs on Chrome OS, dominates the US K–12 education market and represents nearly 20% of the sub-$300 notebook sales in the US. Linux also runs on embedded systems – devices whose operating system is built into the firmware and is highly tailored to the system. This includes TiVo and similar DVR devices, network routers, facility automation controls, televisions, many smartphones and tablet computers run Android and other Linux derivatives. The development of Linux is one of the most prominent examples of free, the underlying source code may be used, modified and distributed—commercially or non-commercially—by anyone under the terms of its respective licenses, such as the GNU General Public License. Typically, Linux is packaged in a known as a Linux distribution for both desktop and server use. Distributions intended to run on servers may omit all graphical environments from the standard install, because Linux is freely redistributable, anyone may create a distribution for any intended use. The Unix operating system was conceived and implemented in 1969 at AT&Ts Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, first released in 1971, Unix was written entirely in assembly language, as was common practice at the time. Later, 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, as a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs, freed of the legal obligation requiring free licensing, the GNU Project, started in 1983 by Richard Stallman, has the goal of creating a complete Unix-compatible software system composed entirely of free software. Later, in 1985, Stallman started the Free Software Foundation, by the early 1990s, many of the programs required in an operating system were completed, although low-level elements such as device drivers, daemons, and the kernel were stalled and incomplete. Linus Torvalds has stated that if the GNU kernel had been available at the time, 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 also stated that if 386BSD had been available at the time, although the complete source code of MINIX was freely available, the licensing terms prevented it from being free software until the licensing changed in April 2000
8.
Sinclair QL
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The Sinclair QL, is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the Sinclair ZX Spectrum. The QL was aimed at the home user and professional and executive users markets from small to large businesses and higher educational establishments. Based on a Motorola 68008 processor clocked at 7.5 MHz, two built-in Microdrive tape-loop cartridge drives provided mass storage, in place of the more expensive floppy disk drives found on similar systems of the era. Interfaces included a slot, ROM cartridge socket, dual RS-232 ports, proprietary QLAN local area network ports, dual joystick ports. Both screen modes used a 32 kB framebuffer in main memory, the hardware is capable of switching between two different areas of memory for the framebuffer, thus allowing double buffering. However, this would have used 64 KB of the standard machines 128 kB of RAM, the alternative and much improved operating system Minerva does provide full support for the second framebuffer. When connected to a normally-adjusted TV or monitor, the QLs video output would overscan horizontally and this was reputed to have been due to the timing constants in the ZX8301 chip being optimised for the flat-screen CRT display originally intended for the QL. Internally, the QL comprised the CPU, two ULAs, and an Intel 8049 microcontroller, the ZX8301 or Master Chip implemented the video display generator and also provided DRAM refresh. The ZX8302, or Peripheral Chip, interfaced to the RS-232 ports Microdrives, QLAN ports, real-time clock, the 8049 ran at 11 MHz and acted as a keyboard/joystick interface, RS-232 receive buffer and audio generator. The QL was bundled with a suite written by Psion. The QL used British Telecom type 631W plugs for serial cables except for QLs built by Samsung for export markets, joysticks connected to the QL with similar type 630W plugs. The QL was originally conceived in 1981 under the code-name ZX83, as a computer for business users, with a built-in ultra-thin flat-screen CRT display, printer. As development progressed it became clear that the portability features were over-ambitious. The electronics were designed by David Karlin, who joined Sinclair Research in summer 1982. The industrial design was done by Rick Dickinson, who designed the ZX81. Sinclair had commissioned GST Computer Systems to produce the system for the machine. GSTs OS, designed by Tim Ward, was made available as 68K/OS. The tools developed by GST for the QL would later be used on the Atari ST, the QL was designed to be more powerful than the IBM Personal Computer, and comparable to Apples Macintosh
9.
Berkeley Software Distribution
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Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995. Today the term BSD is often used non-specifically to refer to any of the BSD descendants which together form a branch of the family of Unix-like operating systems, operating systems derived from the original BSD code remain actively developed and widely used. Historically, BSD has been considered a branch of Unix, Berkeley Unix, because it shared the initial codebase, in the 1980s, BSD was widely adopted by vendors of workstation-class systems in the form of proprietary Unix variants such as DEC ULTRIX and Sun Microsystems SunOS. This can be attributed to the ease with which it could be licensed, FreeBSD, OpenBSD, NetBSD, Darwin, and PC-BSD. The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the system, allowing researchers at universities to modify. A larger PDP-11/70 was installed at Berkeley the following year, using money from the Ingres database project, also in 1975, Ken Thompson took a sabbatical from Bell Labs and came to Berkeley as a visiting professor. He helped to install Version 6 Unix and started working on a Pascal implementation for the system, graduate students Chuck Haley and Bill Joy improved Thompsons Pascal and implemented an improved text editor, ex. Other universities became interested in the software at Berkeley, and so in 1977 Joy started compiling the first Berkeley Software Distribution, 1BSD was an add-on to Version 6 Unix rather than a complete operating system in its own right. Some thirty copies were sent out, some 75 copies of 2BSD were sent out by Bill Joy. 2. 9BSD from 1983 included code from 4. 1cBSD, the most recent release,2. 11BSD, was first issued in 1992. As of 2008, maintenance updates from volunteers are still continuing, a VAX computer was installed at Berkeley in 1978, but the port of Unix to the VAX architecture, UNIX/32V, did not take advantage of the VAXs virtual memory capabilities. 3BSD was also alternatively called Virtual VAX/UNIX or VMUNIX, and BSD kernel images were normally called /vmunix until 4. 4BSD, 4BSD offered a number of enhancements over 3BSD, notably job control in the previously released csh, delivermail, reliable signals, and the Curses programming library. In a 1985 review of BSD releases, John Quarterman et al, many installations inside the Bell System ran 4. 1BSD. 4. 1BSD was a response to criticisms of BSDs performance relative to the dominant VAX operating system, the 4. 1BSD kernel was systematically tuned up by Bill Joy until it could perform as well as VMS on several benchmarks. Back at Bell Labs,4. 1cBSD became the basis of the 8th Edition of Research Unix, to guide the design of 4. The committee met from April 1981 to June 1983, apart from the Fast File System, several features from outside contributors were accepted, including disk quotas and job control. Sun Microsystems provided testing on its Motorola 68000 machines prior to release, the official 4. 2BSD release came in August 1983. On a lighter note, it marked the debut of BSDs daemon mascot in a drawing by John Lasseter that appeared on the cover of the printed manuals distributed by USENIX
10.
Computing
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Computing is any goal-oriented activity requiring, benefiting from, or creating a mathematical sequence of steps known as an algorithm — e. g. through computers. The field of computing includes computer engineering, software engineering, computer science, information systems, the ACM Computing Curricula 2005 defined computing as follows, In a general way, we can define computing to mean any goal-oriented activity requiring, benefiting from, or creating computers. For example, an information systems specialist will view computing somewhat differently from a software engineer, regardless of the context, doing computing well can be complicated and difficult. Because society needs people to do computing well, we must think of computing not only as a profession, the fundamental question underlying all computing is What can be automated. The term computing is also synonymous with counting and calculating, in earlier times, it was used in reference to the action performed by mechanical computing machines, and before that, to human computers. Computing is intimately tied to the representation of numbers, but long before abstractions like the number arose, there were mathematical concepts to serve the purposes of civilization. These concepts include one-to-one correspondence, comparison to a standard, the earliest known tool for use in computation was the abacus, and it was thought to have been invented in Babylon circa 2400 BC. Its original style of usage was by lines drawn in sand with pebbles, abaci, of a more modern design, are still used as calculation tools today. This was the first known computer and most advanced system of calculation known to date - preceding Greek methods by 2,000 years. The first recorded idea of using electronics for computing was the 1931 paper The Use of Thyratrons for High Speed Automatic Counting of Physical Phenomena by C. E. Wynn-Williams. Claude Shannons 1938 paper A Symbolic Analysis of Relay and Switching Circuits then introduced the idea of using electronics for Boolean algebraic operations, a computer is a machine that manipulates data according to a set of instructions called a computer program. The program has a form that the computer can use directly to execute the instructions. The same program in its source code form, enables a programmer to study. Because the instructions can be carried out in different types of computers, the execution process carries out the instructions in a computer program. Instructions express the computations performed by the computer and they trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions, computer software or just software, is a collection of computer programs and related data that provides the instructions for telling a computer what to do and how to do it. Software refers to one or more programs and data held in the storage of the computer for some purposes. In other words, software is a set of programs, procedures, algorithms, program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software
11.
Xfce
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Xfce is a free and open-source desktop environment for Unix and Unix-like operating systems, such as Linux, Solaris, and BSD. Xfce aims to be fast and lightweight, while still being visually appealing, Xfce embodies the traditional UNIX philosophy of modularity and re-usability. It consists of separately packaged parts that provide all functions of the desktop environment. Another priority of Xfce is adherence to standards, specifically those defined at freedesktop. org, like GNOME, Xfce is based on the GTK+ toolkit. It uses the Xfwm window manager, described below and its configuration is entirely mouse-driven, with the configuration files hidden from the casual user. Xfce does not feature any desktop animations, but Xfwm supports compositing, olivier Fourdan started the project in 1996 as a Linux version of the Common Desktop Environment, a Unix desktop environment that was initially proprietary and later released as free software. However, after a years of development and several major versions, Xfce has diverged from CDE. The name Xfce originally stood for XForms Common Environment, but since that time Xfce has been rewritten twice, the name survived, but it is no longer capitalized as XFCE, but rather as Xfce. The developers current stance is that the no longer stands for anything specific. It has been nicknamed Cholesterol Free Desktop Environment, another possibility X Freakin Cool Environment is suggested at Xfce Wiki. As a result, Xfce is currently an acronym that doesnt stand for anything, Xfce began as a simple project created with XForms. Olivier Fourdan released the program, which was just a simple taskbar, Fourdan continued developing the project and in 1998, Xfce 2 was released with the first version of Xfces window manager, Xfwm. He requested to have the project included in Red Hat Linux, Red Hat only accepted software that was open source and released under either a GPL or BSD compatible license, whereas, at the time, XForms was closed source and free only for personal use. For the same reason, Xfce was not in Debian before version 3, in March 1999 Fourdan began a complete rewrite of the project based on GTK+, a non-proprietary toolkit rising in popularity. The result was Xfce 3.0, licensed under the GPL, along with being based completely on free software, the project gained GTK+ drag-and-drop support, native language support, and improved configurability. Xfce was uploaded to SourceForge. net in February 2001, starting with version 3.8.1, in version 4.0.0, released 25 September 2003, Xfce was upgraded to use the GTK+2 libraries. Changes in 4.2.0 included a compositing manager for Xfwm which added support for transparency and drop shadows. In January 2007, Xfce 4.4.0 was released and this included the Thunar file manager, a replacement for Xffm
12.
Operating system
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An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. All computer programs, excluding firmware, require a system to function. Operating systems are found on many devices that contain a computer – from cellular phones, the dominant desktop operating system is Microsoft Windows with a market share of around 83. 3%. MacOS by Apple Inc. is in place, and the varieties of Linux is in third position. Linux distributions are dominant in the server and supercomputing sectors, other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can run one program at a time. Multi-tasking may be characterized in preemptive and 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, e. g. Solaris, Linux, 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 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 work in cooperation, they form a distributed system. The technique is used both in virtualization and cloud computing management, and 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 and they are able to operate with a limited number of resources. They are very compact and extremely efficient by design, Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is a 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, 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 run different programs in succession to speed up processing
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