At the beginning of this class, we were talking about all the theme we had to have read for this date. The people were asking their doubts and so. We had been talking about the date of the exam too.
After this we have talk about more exactly themen like a modem, a webblog, rooter, the ADSL, a cookie and the sat access.
Then we can start with the modem:

What is a modem?

Modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.
The most familiar example is a voiceband modem that turns the digital '1s and 0s' of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Serial, or Network connection. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". They can also be classified by Baud, the number of distinct symbols transmitted per second; these numbers are directly connected, but not necessarily in linear fashion (as discussed under Baud.)
Faster modems are used by Internet users every day, notably cable modems and ADSL modems. In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optical fibers. Most intercontinental data links now use optical modems transmitting over undersea optical fibers. Optical modems routinely have data rates in excess of a billion (1x109) bits per second. One kilobit per second (kbit/s or kb/s or kbps) as used in this article means 1000 bits per second and not 1024 bits per second. For example, a 56k modem can transfer data at up to 56,000 bits per second over the phone line.

What about the ADSL?
Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with ADSL in mind, it can generally only be used over short distances, typically less than 3mi (5 km).[citation needed]
At the telephone exchange the line generally terminates at a DSLAM where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL is typically routed over the telephone company's data network and eventually reaches a conventional internet network. In the UK under British Telecom the data network in question is its ATM network which in turn sends it to it's IP network IP Colossus.
How ADSL works
Frequency plan for ADSL. The red area is the frequency range used by normal voice telephony (PSTN), the green (upstream) and blue (downstream) areas are used for ADSL.
ADSL uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user. With standard ADSL (annex A), the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication. Each of these is further divided into smaller frequency channels of 4.3125 kHz. During initial training, the ADSL modem tests which of the available channels have an acceptable signal-to-noise ratio. The distance from the telephone exchange, noise on the copper wire, or interference from AM radio stations may introduce errors on some frequencies. By keeping the channels small, a high error rate on one frequency thus need not render the line unusable: the channel will not be used, merely resulting in reduced throughput on an otherwise functional ADSL connection.
Vendors may support usage of higher frequencies as a proprietary extension to the standard. However, this requires matching vendor-supplied equipment on both ends of the line, and will likely result in crosstalk issues that affect other lines in the same bundle.
There is a direct relationship between the number of channels available and the throughput capacity of the ADSL connection. The exact data capacity per channel depends on the modulation method used.
A common error is to attribute the A in ADSL to the word asynchronous. ADSL technologies use a synchronous framed protocol for data transmission on the wire.

Installation issues


ADSL Router by UTStarcom
Due to the way it uses the frequency spectrum, ADSL deployment presents some issues. It is necessary to install appropriate frequency filters at the customer's premises, to avoid interferences with the voice service, while at the same time taking care to keep a clean signal level for the ADSL connection.
In the early days of DSL, installation required a technician to visit the premises. A splitter was installed near the demarcation point, from which a dedicated data line was installed. This way, the DSL signal is separated earlier and is not attenuated inside the customer premises. However, this procedure is costly, and also caused problems with customers complaining about having to wait for the technician to perform the installation. As a result, many DSL vendors started offering a self-install option, in which they ship equipment and instructions to the customer. Instead of separating the DSL signal at the demarcation point, the opposite is done: the DSL signal is "filtered off" at each phone outlet by use of a low pass filter, also known as microfilter. This method does not require any rewiring inside the customer premises.
A side effect of the move to the self-install model is that the DSL signal can be degraded, especially if more than 5 voiceband devices are connected to the line. The DSL signal is now present on all telephone wiring in the building, causing attenuation and echo. A way to circumvent this is to go back to the original model, and install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some (poorly designed) household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use.




And what about the router?
A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path.[1] They connect networks together; a LAN to a WAN for example, to access the Internet. Some units, like the Cisco 1800 (pictured), are available in both wired and wireless models.
A more precise definition of a router is a computer networking device that interconnects separate logical subnets. Routers are now available in many types, though all are fundamentally doing the same job. A router is a computer whose software and hardware are usually tailored to the tasks of routing and forwarding, generally containing a specialized operating system (e.g. Cisco's IOS or Juniper Networks JUNOS and JUNOSe or Extreme Networks XOS), RAM, NVRAM, flash memory, and one or more processors. High-end routers contain many processors and specialized Application-specific integrated circuits (ASIC) and do a great deal of parallel processing. Chassis based systems like the Nortel MERS-8600 or ERS-8600 routing switch, have multiple ASICs on every module and allow for a wide variety of LAN, MAN, METRO, and WAN port technologies or other connections that are customizable

Types of routers: Routers for Internet connectivity and internal use, Small and Home Office (SOHO) connectivity,

What is a cookie?
HTTP cookies, sometimes known as web cookies or just cookies, are parcels of text sent by a server to a web browser and then sent back unchanged by the browser each time it accesses that server. HTTP cookies are used for authenticating, tracking, and maintaining specific information about users, such as site preferences or the contents of their electronic shopping carts. The term "cookie" is derived from "magic cookie," a well-known concept in unix computing which inspired both the idea and the name of HTTP cookies.
Cookies have been of concern for Internet privacy, since they can be used for tracking browsing behavior. As a result, they have been subject to legislation in various countries such as the United States and in the European Union. Cookies have also been criticised because the identification of users they provide is not always accurate and because they could potentially be used for network attacks. Some alternatives to cookies exist, but each has its own drawbacks.
Cookies are also subject to a number of misconceptions, mostly based on the erroneous notion that they are computer programs. In fact, cookies are simple pieces of data unable to perform any operation by themselves. In particular, they are neither spyware nor viruses, despite the detection of cookies from certain sites by many anti-spyware products.
Most modern browsers allow users to decide whether to accept cookies, but rejection makes some websites unusable. For example, shopping baskets implemented using cookies do not work if cookies are rejected.


Alternatives to cookies
Some of the operations that can be realised using cookies can also be realised using other mechanisms. However, these alternatives to cookies have their own drawbacks, which make cookies usually preferred to them in practice. Most of the following alternatives allow for user tracking, even if not as reliably as cookies. As a result, privacy is an issue even if cookies are rejected by the browser or not set by the server.
IP address
An unreliable technique for tracking users is based on storing the IP addresses of the computers requesting the pages. This technique has been available since the introduction of the World Wide Web, as downloading pages requires the server holding them to know the IP address of the computer running the browser or the proxy, if any is used. This information is available for the server to be stored regardless of whether cookies are used or not.
However, these addresses are typically less reliable in identifying a user than cookies because computers and proxies may be shared by several users, and the same computer may be assigned different Internet addresses in different work sessions (this is often the case for dial-up connections). The reliability of this technique can be improved by using another feature of the HTTP protocol: when a browser requests a page because the user has followed a link, the request that is sent to the server contains the URL of the page where the link is located. If the server stores these URLs, the path of page viewed by the user can be tracked more precisely. However, these traces are less reliable than the ones provided by cookies, as several users may access the same page from the same computer, NAT router, or proxy and then follow two different links. Moreover, this technique only allows tracking and cannot replace cookies in their other uses.
Tracking by IP address can be impossible with some systems that are used to retain Internet anonymity, such as Tor. With such systems, not only could one browser carry multiple addresses throughout a session, but multiple users could appear to be coming from the same IP address, thus making IP address use for tracking wholly unreliable.
Some major ISPs, including AOL, route all web traffic through a small number of proxies which makes this scheme particularly unworkable.
URL (query string)
A more precise technique is based on embedding information into URLs. The query string part of the URL is the one that is typically used for this purpose, but other parts can be used as well. The PHP session mechanism uses this method if cookies are not enabled.
This method consists of the Web server appending query strings to the links of a Web page it holds when sending it to a browser. When the user follows a link, the browser returns the attached query string to the server.
Query strings used in this way and cookies are very similar, both being arbitrary pieces of information chosen by the server and sent back by the browser. However, there are some differences: since a query string is part of a URL, if that URL is later reused, the same attached piece of information is sent to the server. For example, if the preferences of a user are encoded in the query string of a URL and the user sends this URL to another user by e-mail, those preferences will be used for that other user as well.
Moreover, even if the same user accesses the same page two times, there is no guarantee that the same query string is used in both views. For example, if the same user arrives to the same page but coming from a page internal to the site the first time and from an external search engine the second time, the relative query strings are typically different while the cookies would be the same. For more details, see query string.
Other drawbacks of query strings are related to security: storing data that identifies a session in a query string enables or simplifies session fixation attacks, referer logging attacks and other security exploits. Transferring session identifiers as HTTP cookies is more secure.

1.4.2. Drawing from said

The award of texts is not a new invention in the form of sentence and correction instructions, she was an indispensable tool for writers and editors to instructions for the implementation of a manuscript doing.

Even the use of large and small description and bold is a form of the award. Strictly speaking, this is a simple form of physical distinction. Physical award means the document content with certain attributes to the visual representation to describe and has become part of the layout design.


In the data processing called the Mount of tags in a conventional text file also labeling. When tags are instructions, which consist of two parts. In between, there is either plain text or another tag. In the latter case, talk of a so-called nesting of tags. Since Tags also from text drawing, it is necessary that these differ from the rest of the text at once. Usually, in the markup languages, like HTML and the Grösser Kleiner characters. The opposite of a markup language are file formats, a spezific coding. For example, you can expect special HTML tags in a text with a particular font, color and size. The Physical award may also refer the entire document cover. To include tags for the indication of the page width also added. Of the difference between the logical distinction of a text, the structure of a document describes. This includes, for example, headings, lists, paragraphs, Rahemn, lists and references. There is, of course, for a reception by the people sense that this text elements also represent different visually. The term is also awarded in the name HTML: Hyper Text Markup Language.That name is also clear that with this language called Hyper Text, which are non-linear lyrics, excellent. The connections between individual hyper text, called Links, a part of the structure of a hypertext there.

The objective of the award is a logical addition to the structure, above all, a computer-aided processing of hypertext. For various output devices are certain physical representations different. For various output devices are certain physical representations different.
This is in the HTML Cascading Style Sheets are available. This clean segregation of us layout structure is in daily practice in many HTML is not given. Why is that old versions of CSS browser does not support the use of style sheets is still not as widespread.

For the most flexible use is a separation of the structure, content and format requirements.The mixture of structure and format in HTML, despite the obvious disadvantages of not more than initially disturbing. The use of formatting commands within a document was also rather the usual WYSIWYG view and we have not even thought of a treatment for a variety of output devices. In the early days of the Internet was an easy-to-learn and easy-to-use tool also important. Thus wore these design weaknesses of HTML significantly to the spread of the WWW. But the latest labor Creating Web pages, the same treatment content sources for different output devices, the application of existing enterprise Style Guides, version management, and from certain project sizes is a clean separation of the structure, content and layout is essential.

It seems somewhat restrictive, though always of texts such as Hyper text of the speech, it is still at Internet sites throughout today to multimedia presentations. The concept of hypertext, however, to a close only monomediale representation.
The reason for the continued use of the term text is that the description of multimedia web pages also by simple texts.


Besides HTML, there are other ways to multimedia documents to structure and save. Together, these data formats that it is mainly due to a physical description of a document designed:
Word processing programs
Page description languages
Document Formats

In contrast to HTML, it is in these file formats but to no markup languages and the structure, content and the data in a single file.

The possibilities for physical distinction has been in HTML CSS 2.0 a level achieved, even nourished hopes that HTML in the near future as a universal page description language, and as a universal document format will be used. A possible indication of this is in the fact that HTML now all Office-Pakten as of alternative export file format. In contrast to the layout are the tags for structuring content in HTML less advanced . This is not necessarily a disadvantage to be seen as the integration of tags to the physical presentation and the low level language with a reason for the slight learnability of HTML been. In addition, HTML, in contrast to many word processing file formats, Desktop-Publishing file formats to un document formats as a platform file format to be considered.
Due to the limited opportunities for structuring content, the use of HTML for the creation of documents for an information-processing little sense. The commands for structuring a document available on the Internet hypertext designed and authoritatively defined without their own extensions are possible. For the simple publishing documents on the Internet that makes sense. Typical Internet documents are not too large claims in terms of structuring options. Adding custom tags in HTML is not desirable, such as not useful, because yes, the Internet is different clients on a defined standard of the language relate.

Unlike this layout-oriented tasks, but it looks at data-centric tasks.
These are problems, mainly in the storage and transmission of data provided by operating daily incurred. These data have a complex internal structure, and should not be only for a presentation prepared on the Internet, but also the most easily can be processed electronically. A most convenient exchange of documents and an easy-to-use information further processing but also for layout centered desirable. More and more often is for the business daily business, the need for such a layout-oriented software systems within heterogeneous IT infrastructure, but also between the EDV-Lanschaften cooperating organizations.
New technical requirements for such systems also come from the leadership of the organizations themselves: there is a vital interest in data and document centered sources with different formats for the Knowledge-based management systems and to merge and process. But also for a more intelligent "search and find" on the Internet, such as search engines and software agents, HTML is not the ultimate savior.

For these application areas is not only a cross-platform format required, but it also needs to develop a scope of independent us the opportunity provide any bedeutungsspezifische information in a document. In HTML, there are approaches, such as meta tags to describe a document, but they are not expandable. Is a markup language that is not confined to a given grammar and vocabulary is not expandable, but with the possibility of their own markup language to create, which can arbitrarily complex document structures can be mapped.
A markup language that satisfies this is called a meta-language. So far, the most comprehensive approach for such a meta language, SGML (Standard Generalized Markup Language), which build on the work of GML in the year 1986 standard.


SGML is used in many industries for the document management.
Quote value are primarily the automotive and defense industries, which are both due to the complex nature of the early SGML documents for their application areas adapt . The disadvantage of SGML that is a very complex and difficult. This promises to remedy the Extensible Markup Language, with the help of SGML has been defined.



1.4.2.1 Basic concepts of Hypertext Markup Language

In comparison to a conventional desktop publishing Programe are the design options in W3 still some limits. The development and standardization of HTML but is a constant He further ungso rizess
subject, but in addition to the current standard HTML 4.01 and x HTML 1.o of each client developers deviating from the standard implements additional features. With an extensive support of the W • C already standardized CCS-2 is thus a real page design for Web pages possible.

Heading
As the quell code apparent Could the HTML document with any text editor or word processing has been applied. Every HTML document begins with the day </ html>. Too formatted text is basically at the beginning of one-and final-Tag marked with the final-tag a slash (1) are presented. Such a comprehensive text tags are also containers. The opposite of this are tags that are not final-tag, such as the first day in these key from Abb.I-2.7.Das day <DOCTYPE> is optional, and refers to the HTML version, and used language



In actual textteil there is a lot more opportunities, single-day u setzn. Can titles in six different sizes are defined, but the definition of font and size for each <Hx> tags to W3- Clientes can be set. The syntax is <Hx> text </ Hz>, where x is a number between 1 and 6, and the headings - defined level.




To sign so-called style formatting tags are used, the most important are as follows:
- Emphasize
- strong emphasis.
- Bold
- italics



Listen than enumerating lists, numbered lists, or lists of descriptive executed. An enumerative list starts with the

day (Unnumbered List), the individual list entries are like all other forms of Lise with the </ UL> day. Should the individual list entries are numbered, it is with the
day (ordered List), and started with the </ OL> tag. A special case is the descriptive list

(definition list), whose list of entries with

day labeled.

The full hypertext functionality in HTML, but only by the possibility of generating links cross-references) to apply. Links with the day (Anchor). For external links to realize the HREF attribute (Hypertext Reference).

Embedded graphics and multimedia objects. A picture says more than a thousand words and it is also in W3 using HTML embedded in the graphics a key design element. With the optional ALIGN determines whether the following text above, in the middle or bottom of the image to be published.
Multimedia objects are not all W3-Clients processed, but must be equipped with an external helper application or a Browser-Plug-In executed.
A special type of graphics integration are called Click Images, the graphics are, by clicking on the various links different areas can be created.
Frames are long of the most common browsers, and are now at Version 4.0 component of HTML-Sprachumfanges. Previously, the browser manufacturers developed their own language constructs in the Internet clients. At Frames is a possibility of additional design of hypermedia documents. With the help of frames can be a side window into several smaller ones.
Form into HTML documents is a further possibility of interaction in W3. The processing of the data is entered, we at the Clickable images through a server script.


1.4.2.1.1. Cascading Style Sheets

A key feature of a markup language is the separation of HTML is not consistently implemented: There are many tags to layout design. For the separation of layout and structure serve Cascading Style Sheets, with the HTML documents linked, or in an HTML file can be directly involved. The possibilities of using CSS2 come, as far as the client, in the area of layouts far beyond the optical tags for presentation in HTML, and in combination with HTML CSS also suitable as a full page description language, such as PostScript. The issue is not only to a limited visual presentation, there are also commands for the acoustic output.
Style sheets can be in the head define an HTML file, although this format information only for such a file. If you want to have a consistent layout across multiple files, it is necessary that this format definitions in a separate file. The use of multiple CSS files is also possible. This is erfordelich when different style sheets for multiple output devices wishes.
This is true not only for output devices that use different media, but also for output devices, that the same medium. Thus, for example, has an optical output to a printer, unlike on a monitor.

We can not going to this class, and we do not found your email direction to write you an email, so we hope you see this message.

thank you.

During this class we have been talking about the "Datenkompression", and one example we tolk about was the MP3. What is a MP3?

MPEG-1 Audio Layer 3, more commonly referred to as MP3, is an audio encoding format.
It uses a lossy compression algorithm that is designed to greatly reduce the amount of data required to represent the audio recording, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. It was invented by a team of European engineers at Philips, CCETT (Centre commun d'études de télévision et télécommunications), IRT and Fraunhofer Society, who worked in the framework of the EUREKA 147 DAB digital radio research program, and it became an ISO/IEC standard in 1991.
MP3 is an audio-specific format. The compression removes certain parts of sound that are outside the hearing range of most people. It provides a representation of pulse-code modulation — encoded audio in much less space than straightforward methods, by using psychoacoustic models to discard components less audible to human hearing, and recording the remaining information in an efficient manner. This is quite different to the principles used by, say, JPEG, an image compression format, which are purely Frequency Domain based.

Audio quality:
When creating an MP3 file, there is a trade-off between the amount of space used and the sound quality of the result. Typically, the creator of the MP3 file is allowed to set a bit rate, which specifies how many kilobits the file may use per second of audio, for example, when ripping a compact disc to this format. The lower the bit rate used, the lower the audio quality will be, but the smaller the file size. Likewise, the higher the bit rate used, the higher quality, and therefore, larger the file size the resulting MP3 will be.
As described, MP3 files encoded with a lower bit rate will generally play back at a lower quality. With too low a bit rate, "compression artifacts" (i.e., sounds that were not present in the original recording) may be audible in the reproduction. Some audio is hard to compress because of its randomness and sharp attacks. When this type of audio is compressed, artifacts such as ringing or pre-echo are usually heard. A sample of applause compressed with a relatively low bitrate provides a good example of compression artifacts.
Besides the bit rate of an encoded piece of audio, the quality of MP3 files also depends on the quality of the encoder itself, and the difficulty of the signal being encoded. As the MP3 standard allows quite a bit of freedom with encoding algorithms, different encoders may feature quite different quality, even when targeting similar bit rates. As an example, in a public listening test featuring two different MP3 encoders at about 128 kbit/s,[8] one scored 3.66 on a 1–5 scale, while the other scored only 2.22.
Quality is heavily dependent on the choice of encoder and encoding parameters. While quality around 128 kbit/s was somewhere between annoying and acceptable with older encoders, modern MP3 encoders can provide very good quality at those bit rates[9] (January 2006). However, in 1998, MP3 at 128 kbit/s was only providing quality equivalent to AAC-LC at 96 kbit/s and MP2 at 192 kbit/s.[10]




We had been talking also about the construction and the work of the computer systeme: the hardware and the central unit.

Hardware:
physical components of a computer system, in the form of computer hardware. In the electronics and especially computer industries, computer hardware specifically means the physical or tangible parts of the equipment, such as circuit boards, keyboards, monitors etc., in contrast to non-physical software running on the computer or other device.

About the peripheral of a computer, we took the example of a USB.

what is a USB?

Universal Serial Bus (USB) is a serial bus standard to interface devices. A major component in the legacy-free PC, USB was designed to allow peripherals to be connected using a single standardized interface socket and to improve plug-and-play capabilities by allowing devices to be connected and disconnected without rebooting the computer (hot swapping). Other convenient features include providing power to low-consumption devices without the need for an external power supply and allowing many devices to be used without requiring manufacturer specific, individual device drivers to be installed.
USB is intended to help retire all legacy varieties of serial and parallel ports. USB can connect computer peripherals such as mouse devices, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers and flash drives. For many of those devices USB has become the standard connection method. USB is also used extensively to connect non-networked printers; USB simplifies connecting several printers to one computer. USB was originally designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles. In 2004, there were about 1 billion USB devices in the world.[1]
The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Apple Inc., Hewlett-Packard, NEC, Microsoft, Intel, and Agere.

Overview:
A USB system has an asymmetric design, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs may be included in the tiers, allowing branching into a tree structure, subject to a limit of 5 levels of tiers. USB host may have multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including the hub devices, may be connected to a single host controller.
USB devices are linked in series through hubs. There always exists one hub known as the root hub, which is built-in to the host controller. So-called "sharing hubs" also exist; allowing multiple computers to access the same peripheral device(s), either switching access between PCs automatically or manually. They are popular in small-office environments. In network terms they converge rather than diverge branches.
A single physical USB device may consists of several logical sub-devices that are referred to as device functions, because each individual device may provide several functions, such as a webcam (video device function) with a built-in microphone (audio device function).



The rest of the class we were talking about the operating system.

An operating system (OS) is the software that manages the sharing of the resources of a computer. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking and managing file systems. Most operating systems come with an application that provides a user interface for managing the operating system, such as a command line interpreter or graphical user interface. The operating system forms a platform for other system software and for application software.
The most commonly-used contemporary desktop OS is Microsoft Windows, with Mac OS X also being well-known. Linux and the BSD derivatives are popular Unix-like systems
Modern operating systems usually feature a Graphical user interface (GUI) which uses a pointing device such as a mouse or stylus for input in addition to the keyboard. Older models and Operating Systems not designed for direct-human interaction (such as web-servers) generally use a Command line interface (or CLI) typically with only the keyboard for input. Both models are centered around a "shell" which accepts and processes commands from the user (eg. clicking on a button, or a typed command at a prompt).
The choice of OS may be dependant on the hardware architecture, specifically the CPU, with only Linux and BSD running on almost any CPU. Windows NT 3.1, which is no longer supported, was ported to the DEC Alpha and MIPS Magnum. Since the mid-1990s, the most commonly used operating systems have been the Microsoft Windows family, Linux, and other Unix-like operating systems, most notably Mac OS X. Mainframe computers and embedded systems use a variety of different operating systems, many with no direct connection to Windows or Unix. QNX and VxWorks are two common embedded operating systems, the latter being used in network infrastructure hardware equipment.