Dell Computers

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A desktop computer is a personal computer made for use on a desk in an office or home and is distinguished from portable computers such as laptops or PDAs. Desktop computers are also known as microcomputers. There are four types of desktop computers: home computers, or personal computers; workstations, Internet servers, and special communications computers.

Desktops are currently the most affordable computers and ubiquitous in businesses, schools, and households; they are used for performing office tasks, organizing digital photos, video editing, and Internet access. Nearly all desktop computers are modular, with components that can easily be replaced or upgraded.

Desktop computers come in a variety of case styles ranging from large vertical towers to small form factor models that can be tucked behind an LCD monitor.

Desktop computers are commonly connected to a power strip.

History
Desktop computers were widely produced throughout the late 1970s and 1980s. One class that Hewlett Packard first introduced as a high-end programmable calculator was the HP 9830 which integrated a keyboard, ROM based HP BASIC OS, cassette drive, and 32 character LED display and a fast printer into one desktop unit, and could drive a graphics plotter. The business unit in Loveland, Colorado that produced the series was called HP's "Desktop Computer Division". The IBM 5100, Wang 2200, and Tektronix 4051 were similar desktop sized integrated computers, some of which evolved into scientific workstations or small business computers.

Modular boxes that needed external storage and terminals were named "microcomputers" to differentiate them from the mainframe and minicomputers that were traditionally available for sale by the major computer companies at the time. In 1975 the MITS Altair 8800 became the first pre-assembled desktop computer available on the market. However, due to the computer's design being geared more towards the hobbyist market the appeal of the machine was limited.

1977 saw the near-simultaneous release in the U.S. of three computers that equally deserve mention as the forerunners of today's desktop computer: the Apple II, the Commodore PET. and the Tandy TRS-80 computer. Each of these machines would be considered crude by today's standards; the TRS-80, for example, comprised a green phosphor 12" screen, an expansion box with 4 kilobytes of memory, a keyboard and a cassette recorder. It retailed for around £695. These computers also integrated display memory, keyboard, and sometimes storage and CRT into one unit.

Through the 1980s the desktop computer became more and more commonplace in society. Sales boomed as a wide spectrum of users, from the largest corporation down to the individual at home, found exciting new uses for the machines. However, it was not until the internet explosion in the mid-1990s that the desktop computer became nearly ubiquitous in our modern era.

Hardware:

The hardware in a desktop computer is modular, making it easy for someone with intermediate knowledge of a computer to modify one. Desktop computers are generally more affordable than notebook computers. This is because no extra effort is needed to miniaturize the components, or to manufacture components that use up less power.

Components
Fan - cools the computer. These are present on most computers. There are often multiple, one to cool the processor(see below), one in the power supply, and possibly additional ones for the graphics card and general cooling.
Motherboard (a.k.a. Mainboard) - links all of the components together and routes data.
HDD (Hard Disk Drive) - location where all information can be stored even when power is off.
ODD (Optical Disc Drive) - reads most or all types of CDs and/or DVDs.
Processor - The main brain of the computer.
CPU Cooler - cools the processing unit. Typically a fan combined with a heatsink.
RAM - short-term data storage, which works only when power is on.
Graphics card - codes video output and delivers to monitor.
Physics card - performs physics computations in some modern games.
Sound card - codes sound output and delivers to speakers.
Speakers - deliver sound.
Modem - used to access data via a telephone line (dial-up connection). Used to access BBS and the Internet.
Network card - allows the computer to be linked to a computer network where it can communicate with other computers. Also used as a means of accessing the Internet via a broadband connection.
Computer PSU (Power Supply Unit) - A device that provides power to the rest of the computer parts.
FDD (Floppy Disk Drive) - Reads and Writes floppy disks. Although largely supplanted by CDs and Flash Drives, is still common on many systems, and may be required during set-up on certain operating systems.

All-in-one computers are desktop computers that combine the monitor into the same case as the CPU. The term, "all-in-one" was initially associated with Digital Equipment Corporation's VAX "all-in-one" software which provided a common menu to choose: email, spreadsheet, database, file system, etc. The "mouse" had not been invented yet so everything was driven by the keyboard. The original Macintosh introduced in 1984 by Apple Computer was one of the first all-in-one computers, In 1998 Apple released the iMac which was also an all-in-one computer. These types of desktop computers save desk space, but are limited when it comes to expansion to improve their capabilities. Some PC and refrigerator manufacturers have even included full featured PCs and monitors in refrigerators which could be considered all-in-one.

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A laptop computer, or simply laptop (also notebook computer or notebook), is a small mobile computer, which usually weighs 2.2-18 pounds (1-6 kilograms), depending on size, materials, and other factors.

While the terms laptop and notebook are often used interchangeably, "laptop" is the older term, introduced in 1981 with the Gavilan SC. "Notebook computer" is a later coinage, which was used to differentiate smaller devices such as those of the NEC UltraLite and Compaq LTE series in 1989, which were, in contrast to previous laptops, the approximate size of an A4 or letter size paper sheet. The terms are imprecise: due to heat and other issues, many laptops are inappropriate for use on one's lap, and most notebooks are not the size of typical letter or A4 paper notebook. Although some older portable computers, such as the Macintosh Portable and certain Zenith TurbosPort models, were sometimes described as "laptops", their size and weight were too great for this category.

As of 2007, most manufacturers use the term "notebook" (or some variant thereof) for what most end-users call a "laptop".

Laptops usually run on a single main battery or from an external AC/DC adapter which can charge the battery while also supplying power to the computer itself. Many computers also have a 3volt cell to run the clock and other processes in the event of a power failure.

As personal computers, laptops are capable of the same tasks as a desktop computer, although they are typically less powerful for the same price. They contain components that are similar to their desktop counterparts and perform the same functions, but are miniaturized and optimized for mobile use and efficient power consumption. Laptops usually have liquid crystal displays and most of them use different memory modules for their random access memory (RAM), for instance, SO-DIMM in lieu of the larger DIMMs. In addition to a built-in keyboard, they may utilize a touchpad (also known as a trackpad) or a pointing stick for input, though an external keyboard or mouse can usually be attached.

Many schools have taken in laptop based programs in which every student receives a laptop for school use only. The operating system is configured (or a third party program is installed) to limit the student's access to perform administrative tasks such as hardware or software installation, or operating system modifications. Students are generally permitted to use these systems to take notes, write papers, and perform other school-related activities.

History:

Before laptop/notebook computers were technically feasible, similar ideas had been proposed, most notably Alan Kay's Dynabook concept, developed at Xerox PARC in the early 1970s.

The first commercially available portable computer was the Osborne 1 in 1981, which used the CP/M operating system. Although it was large and heavy compared to today's laptops, with a tiny CRT monitor, it had a near-revolutionary impact on business, as professionals were able to take their computer and data with them for the first time. This and other "luggables" were inspired by what was probably the first portable computer, the Xerox NoteTaker, again developed at Xerox PARC, in 1976; however, only ten prototypes were built. The Osborne was about the size of a portable sewing machine, and importantly could be carried on a commercial aircraft. However, it was not possible to run the Osborne on batteries; it had to be plugged in.

A more enduring success was the Compaq Portable, the first product from Compaq, introduced in 1983, by which time the IBM Personal Computer had become the standard platform. Although scarcely more portable than the Osborne machines, and also requiring AC power to run, it ran MS-DOS and was the first true IBM clone (IBM's own later Portable Computer, which arrived in 1984, was notably less IBM PC-compatible than the Compaq).

Another significant machine announced in 1981, although first sold widely in 1983, was the Epson HX-20. A simple handheld computer, it featured a full-transit 68-key keyboard, rechargeable nickel-cadmium batteries, a small (120 x 32-pixel) dot-matrix LCD display with 4 lines of text, 20 characters per line text mode, a 24 column dot matrix printer, a Microsoft BASIC interpreter, and 16 KiB of RAM (expandable to 32 KiB).

However, arguably the first true laptop was the GRiD Compass 1101, designed by Bill Moggridge in 1979-1980, and released in 1982. Enclosed in a magnesium case, it introduced the now familiar clamshell design, in which the flat display folded shut against the keyboard. The computer could be run from batteries, and was equipped with a 320×200-pixel plasma display and 384 kibibyte bubble memory. It was not IBM-compatible, and its high price (US$ 8-10,000) limited it to specialized applications. However, it was used heavily by the U.S. military, and by NASA on the Space Shuttle during the 1980s. The GRiD's manufacturer subsequently earned significant returns on its patent rights as its innovations became commonplace. GRiD Systems Corp. was later bought by Tandy (RadioShack).

Two other noteworthy early laptops were the Sharp PC-5000 and the Gavilan SC, announced in 1983 but first sold in 1984. The Gavilan was notably the first computer to be marketed as a "laptop". It was also equipped with a pioneering touchpad-like pointing device, installed on a panel above the keyboard. Like the GRiD Compass, the Gavilan and the Sharp were housed in clamshell cases, but they were partly IBM-compatible, although primarily running their own system software. Both had LCD displays, and could connect to optional external printers.

The year 1983 also saw the launch of what was probably the biggest-selling early laptop, the Kyocera Kyotronic 85, which owed much to the design of the previous Epson HX-20. Although it was at first a slow seller in Japan, it was quickly licensed by Tandy Corporation, Olivetti, and NEC, which saw its potential and marketed it respectively as TRS-80 Model 100 line (or Tandy 100), Olivetti M-10, NEC PC-8201. The machines ran on standard AA batteries. The Tandy's built-in programs, including a BASIC interpreter, a text editor, and a terminal program, were supplied by Microsoft, and are thought to have been written in part by Bill Gates himself. The computer was not a clamshell, but provided a tiltable 8×40-character LCD screen above a full-travel keyboard. With its internal modem, it was a highly portable communications terminal. Due to its portability, good battery life (and ease of replacement), reliability (it had no moving parts), and low price (as little as US$ 300), the model was highly regarded, becoming a favorite among journalists. It weighed less than 2 kg with dimensions of 30 × 21.5 × 4.5 cm (12 × 8.5 × 1.75 inches). Initial specifications included 8 kibibytes of RAM (expandable to 24 KiB) and a 3 MHz processor. The machine was in fact about the size of a paper notebook, but the term had yet to come into use and it was generally described as a "portable" computer.

Among the first commercial IBM-compatible laptops were the IBM PC Convertible, introduced in 1986, and two Toshiba models, the T1000 and T1200, introduced in 1987. Although limited floppy-based DOS machines, with the operating system stored in read-only memory, the Toshiba models were small and light enough to be carried in a backpack, and could be run off lead-acid batteries. These also introduced the now-standard "resume" feature to DOS-based machines: the computer could be paused between sessions, without having to be restarted each time.

Another early laptop was the Dulmont Magnum, made in Australia and launched internationally in 1984 .

The first laptops successful on a large scale came in large part due to a Request For Proposal (RFP) by the U.S. Air Force in 1987. This contract would eventually lead to the purchase of over 200,000 laptops. Competition to supply this contract was fiercely contested and the major PC companies of the time; IBM, Toshiba, Compaq, NEC, and Zenith Data Systems (ZDS), rushed to develop laptops in an attempt to win this deal. ZDS, which had earlier won a landmark deal with the IRS for its Z-171, was awarded this contract for its SupersPort series. The SupersPort series was originally launched with an Intel 8086 processor, dual floppy disk drives, a backlit, blue and white STN LCD screen, and a NiCD battery pack. Later models featured an Intel 80286 processor and a 20 MB hard disk drive. On the strength of this deal, ZDS became the world's largest laptop supplier in 1987 and 1988.

ZDS partnered with Tottori Sanyo in the design and manufacturing of these laptops. This relationship is notable because it was the first deal between a major brand and an Asian OEM (Original Equipment Manufacturer). At the time, Compaq, IBM, Toshiba, NEC, etc. all designed and manufactured their own machines. However, after the success of the ZDS offering other relationships, like Compaq and Citizen, soon followed. At this time the quality of Japanese engineering and manufacturing in conjunction with the strength of the dollar relative to the yen (typically about 130 Yen = $1) drove most brands to suppliers in Japan. Companies such as Sanyo, Tottori Sanyo, Citizen, and Casio were all heavily involved in this business as OEMs. However, by the mid-1990s a weakening dollar and the rising viability of Taiwanese OEMs such as Acer, Quanta, Compal, Twinhead, and Chicony lead the supply base to rapidly shift from Japan to Taiwan. Additionally, brands which were more nimble and relied less on internal engineering such as Gateway, Dell and Micron began to rise quickly to leadership positions. Combinations such as Dell/Compal and Gateway/Quanta eventually became powerhouse partnerships and greatly contributed to the prominence of Taiwanese OEMs as the center of PC manufacturing from about 1995 onward.

Another notable computer was the Cambridge Z88, designed by Clive Sinclair, introduced in 1988. About the size of an A4 sheet of paper as well, it ran on standard batteries, and contained basic spreadsheet, word processing, and communications programs. It anticipated the future miniaturization of the portable computer; and, as a ROM-based machine with a small display, can — like the TRS-80 Model 100 — also be seen as a forerunner of the personal digital assistant.

By the end of the 1980s, laptop computers were becoming popular among business people. The NEC UltraLite, released in mid-1989, was perhaps the first notebook computer, weighing just over 2 kg; in lieu of a floppy or hard drive, it contained a 2 mebibyte RAM drive, but this reduced its utility as well as its size. The first notebook computers to include hard drives were those of the Compaq LTE series, introduced toward the end of that year. Truly the size of a notebook, they also featured grayscale backlit displays with CGA resolution.

The first Apple Computer machine designed to be used on the go was the 1989 Macintosh Portable (although an LCD screen had been an option for the transportable Apple IIc in 1984). Actually a "luggable", the Mac Portable was praised for its clear active matrix display and long battery life, but was a poor seller due to its bulk. In the absence of a true Apple laptop, several compatible machines such as the Outbound Laptop were available for Mac users; however, for copyright reasons, the user had to supply a set of Mac ROMs, which usually meant having to buy a new or used Macintosh as well.

The Apple PowerBook series, introduced in October 1991, pioneered changes that are now de facto standards on laptops, such as the placement of the keyboard, room for palm rest, and the inclusion of a built-in pointing device (a trackball). The following year, IBM released its Thinkpad 700C, featuring a similar design (though with a distinctive red TrackPoint pointing device).

Later PowerBooks introduced the first 256-color displays (PowerBook 165c, 1993), and first true touchpad, first 16-bit sound recording, and first built-in Ethernet network adapter (PowerBook 500, 1994).

The summer of 1995 was a significant turning point in the history of notebook computing. In August of that year Microsoft introduced Windows 95. It was the first time that Microsoft had placed much of the power management control in the operating system. Prior to this point each brand used custom BIOS, drivers and in some cases, ASICs, to optimize the battery life of its machines. This move by Microsoft was controversial in the eyes of notebook designers because it greatly reduced their ability to innovate; however, it did serve its role in simplifying and stabilizing certain aspects of notebook design. Windows 95 also ushered in the importance of the CD-ROM drive in mobile computing and initiated the shift to the Intel Pentium processor as the base platform for notebooks. The Gateway Solo was the first notebook introduced with a Pentium processor and a CD-ROM. By also featuring a removable hard disk drive and floppy drive it was the first three-spindle (optical, floppy, and hard disk drive) notebook computer. The Gateway Solo was extremely successful within the consumer segment of the market. In roughly the same time period the Dell Latitude, Toshiba Satellite, and IBM Thinkpad were reaching great success with Pentium-based two-spindle (hard disk and floppy disk drive) systems directed toward the corporate market.

As technology improved during the 1990s, the usefulness and popularity of laptops increased. Correspondingly prices went down. Several developments specific to laptops were quickly implemented, improving usability and performance. Among them were:

Improved battery technology. The heavy lead-acid batteries were replaced with lighter and more efficient technologies, first nickel cadmium or NiCD, then nickel metal hydride (NiMH) and then lithium ion battery and lithium polymer.
Power-saving processors. While laptops in 1991 were limited to the 80286 processor because of the energy demands of the more powerful 80386, the introduction of the Intel 386SL processor, designed for the specific power needs of laptops, marked the point at which laptop needs were included in CPU design. The 386SL integrated a 386SX core with a memory controller and this was paired with an I/O chip to create the SL chipset. It was more integrated than any previous solution although its cost was higher. It was heavily adopted by the major notebook brands of the time. Intel followed this with the 486SL chipset which used the same architecture. However, Intel had to abandon this design approach as it introduced its Pentium series. Early versions of the mobile Pentium required TAB mounting (also used in LCD manufacturing) and this initially limited the number of companies capable of supplying notebooks. However, Intel did eventually migrate to more standard chip packaging. One limitation of notebooks has always been the difficulty in upgrading the processor which is a common attribute of desktops. Intel did try to solve this problem with the introduction of the MMC for mobile computing. The MMC was a standard module upon which the CPU and external cache memory could sit. It gave the notebook buyer the potential to upgrade his CPU at a later date, eased the manufacturing process some, and was also used in some cases to skirt U.S. import duties as the CPU could be added to the chassis after it arrived in the U.S. Intel stuck with MMC for a few generations but ultimately could not maintain the appropriate speed and data integrity to the memory subsystem through the MMC connector.
Improved liquid crystal displays, in particular active-matrix TFT (Thin-Film Transistor) LCD technology. Early laptop screens were black and white, blue and white, or grayscale, STN (Super Twist Nematic) passive-matrix LCDs prone to heavy shadows, ghosting and blurry movement (some portable computer screens were sharper monochrome plasma displays, but these drew too much current to be powered by batteries). Color STN screens were used for some time although their viewing quality was poor. By about 1991 , two new color LCD technologies hit the mainstream market in a big way; Dual STN and TFT. The Dual STN screens solved many of the viewing problems of STN at a very affordable price and the TFT screens offered excellent viewing quality although initially at a steep price. DSTN continued to offer a significant cost advantage over TFT until the mid-90s before the cost delta dropped to the point that DSTN was no longer used in notebooks. Improvements in production technology meant displays became larger, sharper, had higher native resolutions, faster response time and could display color with great accuracy, making them an acceptable substitute for a traditional CRT monitor.
Improved hard disk technology. Early laptops and portables had only floppy disk drives. As thin, high-capacity hard disk drives with higher reliability and shock resistance and lower power consumption became available, users could store their work on laptop computers and take it with them. The 3.5" HDD was created initially as a response to the needs of notebook designers that needed smaller, lower power consumption products. With continuing pressure to shrink the notebook size even further, the 2.5" HDD was introduced.
Improved connectivity. Internal modems and standard serial, parallel, and PS/2 ports on IBM PC-compatible laptops made it easier to work away from home; the addition of network adapters and, from 1997, USB, as well as, from 1999, Wi-Fi, made laptops as easy to use with peripherals as a desktop computer.

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An application server is a software engine that delivers applications to client computers or devices. Moreover, an application server handles most, if not all, of the business logic and data access of the application (A.K.A. centralization). The main benefit of application servers are the ease of application development. Application development is made easier because applications are not programmed; instead, they are assembled from the many building blocks that the application server provides.

Although the term application server applies to all platforms, it has become heavily identified with the Sun Microsystems J2EE platform; however, it has also come to encompass servers of web-based applications, such as integrated platforms for e-commerce, content management systems, affiliate management systems, and simple web-site builders. The paradigm is a throw-back to mainframe based applications while maintaining the benefits of client-server computing.

Communications servers are open, standards-based computing systems that operate as a carrier-grade common platform for a wide range of communications applications and allow equipment providers to add value at many levels of the system architecture.

Based on industry-managed standards such as AdvancedTCA®, MicroTCATM, Carrier Grade Linux and Service AvailabilityTM Forum specifications, communications servers are the foundational platform upon which equipment providers build network infrastructure elements for deployments such as IP Multimedia Subsystem (IMS), IPTV and wireless broadband (e.g. WiMAX).

By driving down infrastructure costs, improving time to market, and shifting user resources toward the development of new applications and services, communications servers will help accelerate the cost effective deployment of converged services.

Support for communications servers as a category of server is developing rapidly throughout the communications industry. Standards bodies, industry associations, vendor alliance programs, hardware and software manufacturers, communications server vendors and users are all part of an increasingly robust communications server ecosystem.

Regardless of their specific, differentiated features, communications servers have the following attributes: open, flexible, carrier-grade, and communications-focused.

A database server is a computer program that provides database services to other computer programs or computers, as defined by the client-server model. The term may also refer to a computer dedicated to running such a program. Database management systems frequently provide database server functionality, and some DBMS's (e.g., MySQL) rely exclusively on the client-server model for database access.

Database Master servers are central and main locations of data while Database Slave servers are synchronized backups of the master acting as proxies.

In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by making requests to other servers. A client connects to the proxy server, requesting a file, connection, web page, or other resource available from a different server. A proxy server provides the resource by connecting to the specified server, with some exceptions: A proxy server may alter the client's request or the server's response. A proxy server may service the request without contacting the specified server.

(A proxy server that passes all requests and replies unmodified is not called a proxy server. It is a gateway.)

A proxy server can be placed in the user's local computer, or at specific key points between the user and the destination servers or the Internet.

A game server is a server used by game clients. Any video game played over the internet generally requires a connection to a game server.

How it works
Data is sent from the game client to the game server, from there the game server processes the data and sends it back out to the client or clients. Game servers often require large amounts of bandwidth due to the amount of data that has to be sent between the server and all the clients that are connected to it.

Standalone servers are compilations of programs that run on a single PC, but emulates what the same set of programs will do when run on a server over the Internet. They usually contain a web server (such as the Apache HTTP Server), one or more languages, and one or more databases.

The term Web server can mean one of two things:

A computer that is responsible for accepting HTTP requests from clients, which are known as Web browsers, and serving them HTTP responses along with optional data contents, which usually are Web pages such as HTML documents and linked objects (images, etc.).
A computer program that provides the functionality described in the first sense of the term.


Client server is network architecture which separates a client (often an application that uses a graphical user interface) from a server. Each instance of the client software can send requests to a server. Specific types of servers include web servers, application servers, file servers, terminal servers, and mail servers. While their purposes vary somewhat, the basic architecture remains the same.

Although this idea is applied in a variety of ways, on many different kinds of applications, an easy example to visualize is an internet site. For instance, if you are browsing an online store, your computer and web browser would be considered a client, and the computers, databases, and applications that make up the online store would be considered the server. When your web browser requests a particular page from the online store, the server finds all of the information required to display the article in the database, assembles it into a web page, and sends it back to your web browser for you to look at.

A peer-to-peer server (or P2P) computer network relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers. P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using P2P technology.

A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server. A typical example for a non peer-to-peer file transfer is an FTP server where the client and server programs are quite distinct, and the clients initiate the download/uploads and the servers react to and satisfy these requests.

The earliest peer to-peer network in widespread use was the Usenet news server system, in which peers communicated with one another to propagate Usenet news articles over the entire Usenet network. Particularly in the earlier days of Usenet, UUCP was used to extend even beyond the Internet. However, the news server system also acted in a client-server form when individual users accessed a local news server to read and post articles. The same consideration applies to SMTP email in the sense that the core email relaying network of Mail transfer agents is a peer-to-peer network while the periphery of Mail user agents and their direct connections is client server.

Some networks and channels such as Napster, OpenNAP and IRC server channels use a client-server structure for some tasks (e.g. searching) and a peer-to-peer structure for others. Networks such as Gnutella or Freenet use a peer-to-peer structure for all purposes, and are sometimes referred to as true peer-to-peer networks, although Gnutella is greatly facilitated by directory servers that inform peers of the network addresses of other peers.

Peer-to-peer architecture embodies one of the key technical concepts of the internet, described in the first internet Request for Comments, RFC 1, "Host Software" dated 7 April 1969. More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing servers in architectures used for exchanging multimedia files.

The concept of peer to peer is increasingly evolving to an expanded usage as the relational dynamic active in distributed networks, i.e. not just computer to computer, but human to human. Yochai Benkler has coined the term "commons-based peer production" to denote collaborative projects such as free software. Associated with peer production are the concept of peer governance (referring to the manner in which peer production projects are managed) and peer property (referring to the new type of licenses which recognize individual authorship but not exclusive property rights, such as the GNU General Public License and the Creative Commons License).