Web server

What a web server is

“Web server” can mean a program, a computer or the two working together. MDN Web Docs, Mozilla’s reference for web developers, describes the hardware as a computer that stores web server software and a website’s files, such as HTML documents, images, CSS style sheets and JavaScript files, and that is connected to the internet.¹

On the software side, the core part is an HTTP server: a program that understands web addresses, called URLs, and HTTP, the protocol browsers use to fetch pages.¹ The HTTP standard, RFC 9110, defines a server as “a program that accepts connections in order to service HTTP requests by sending HTTP responses.”²

The same standard uses the term origin server for the program that can give the authoritative answer for a page or file.² Other machines may sit between the visitor and the origin server, as later sections explain. In this entry, “web server” means the software unless the text says “machine.”

One machine can run websites for many different owners. Apache’s documentation calls this virtual hosting: running sites such as company1.example.com and company2.example.com on a single machine, either with a separate IP address for each site or with many names sharing one address. Visitors cannot tell that the sites share hardware.³ This is how many small sites can share one web hosting server.

How a web server answers a request

A page visit starts when a web browser asks for a file over HTTP. When the request reaches the right machine, the HTTP server accepts it, finds the document and sends it back, also over HTTP.¹ If no port is named in the address, plain HTTP uses TCP port 80 and HTTPS uses TCP port 443.²

MDN breaks the server’s decision into three steps:¹

1. It checks whether the requested URL matches a file it holds.
2. If it does, it sends that file. If not, it checks whether it should build a response for this request instead.
3. If it can do neither, it sends an error, most often 404 Not Found.

A server has to answer every request, even if only with an error message.¹ The server’s settings decide how addresses map to folders. In an example from the Nginx guide, a request for /images/example.png is answered with the file /data/images/example.png on the server’s disk.⁴

Every response begins with a three-digit status code. Codes fall into five classes: 100 to 199 are informational, 200 to 299 mean success, 300 to 399 are redirects, 400 to 499 are client errors and 500 to 599 are server errors.⁵ Common examples are 200 OK, 301 Moved Permanently (the page has a new permanent address, which the response gives), 404 Not Found and 503 Service Unavailable, which means the server is not ready, often because it is overloaded or down for maintenance.⁵

Many servers also name themselves in a Server response header, with a value such as Apache/2.4.1 (Unix).⁶ MDN warns that a detailed version number in this header can make known vulnerabilities easier to spot, and advises keeping the software patched, since servers can be identified in other ways too.⁶

Busy servers must answer many visitors at once, and two broad designs exist. In a process-based design such as Apache’s prefork module, a parent process keeps a pool of server processes, and each of them answers requests.⁷ In an event-driven design such as Nginx’s, each worker process handles many connections without waiting on any one of them; the Nginx team says this scales to “hundreds of thousands of connections per worker process.”⁸

Static and dynamic responses

MDN calls a server static when it “sends its hosted files as-is” to the browser.¹ A dynamic server adds more software, most often an application server and a database. The application server builds or updates the page before the HTTP server sends it, for example by filling an HTML template with text from the database.¹

The idea of building pages on request is as old as the web. In his public announcement of August 6, 1991, Tim Berners-Lee wrote that a server could generate hypertext on the fly from other data, and pointed to a server already doing this on CERN’s mainframe.⁹

An early and widely used method for this was the Common Gateway Interface, or CGI, a simple way for a web server to run an outside program and send back its output. RFC 3875, published in October 2004, documents CGI version 1.1, which was developed at the U.S. National Center for Supercomputing Applications (NCSA) and had been in use on the web since 1993.¹⁰ The CERN server’s change history records CGI/1.0 as “fully implemented” in version 2.15beta, dated February 11, 1994.¹¹

Today the web server and the program that builds pages are often separate. The Nginx guide shows a setup in which Nginx serves image files from disk itself and passes every other request to a FastCGI server, a separate program such as a PHP process, listening on port 9000 of the same machine.⁴

Some applications skip the separate web server altogether. Node.js, a runtime that runs JavaScript outside the browser, has a built-in http module; its own introduction shows a short program that answers “Hello World” on port 3000.¹² W3Techs counts Node.js as the web server on 7.4% of websites whose server it can identify, as of October 22, 2026.¹³

The first web server: CERN httpd

Berners-Lee developed the code for the first web server on a NeXT computer at CERN, and by the end of 1990 he had the first web server and browser running there.¹⁴ The W3C’s history dates the first server, nxoc01.cern.ch, later called info.cern.ch, and the first web page to November 1990.¹⁵ The machine carried a handwritten label telling people not to power it down, and it is still kept at CERN.¹⁴¹⁶

CERN’s 1991 release of the web software included the line-mode browser, web server software and a code library for developers.¹⁴ Berners-Lee’s August 1991 post described the server as a way to make files available “like anonymous FTP but faster because it only uses one connection.”⁹

That program became known as CERN httpd, short for HTTP daemon, a daemon being a program that runs in the background waiting for requests. W3C lists its authors as Ari Luotonen, Henrik Frystyk Nielsen and Tim Berners-Lee.¹⁷ Luotonen joined CERN in July 1993, added access control and rewrote the server.¹⁵ Its change history shows how quickly the basic features of a web server took shape:¹¹

• Version 0.1 (June 1991): command-line options for rule files and for logging to a file.
• 2.12 (October 11, 1993): the first release with access authorization, meaning password protection.
• 2.14 (November 16, 1993): support for forms from the Mosaic browser and clickable images.
• 2.15beta (February 11, 1994): CGI/1.0, redirection and the common log format.
• 2.16beta (February 28, 1994): caching when working as a proxy.

W3C describes the finished program as a full-featured server that could also work as a proxy for HTTP, FTP, Gopher, WAIS and news, caching documents as it went.¹⁷ CERN ended its direct work on the server with version 3.0, and development moved to the W3C.¹¹ The final version, 3.0A, was generated on July 15, 1996. W3C no longer maintains it and moved its own server work to Jigsaw, a server written in Java.¹⁷

The number of servers grew fast. Paul Kunz set up the first web server outside Europe, at SLAC, on December 12, 1991.¹⁵ The W3C history counts about 50 known HTTP servers in January 1993, over 200 in October 1993 and over 1,500 registered servers in June 1994.¹⁵ CERN’s own history gives higher figures: over 500 known servers by late 1993 and 10,000 by the end of 1994.¹⁴

On April 30, 1993, CERN made the web’s source code available royalty-free.¹⁴ W3C’s page calls CERN httpd a public domain server, while also noting that it is covered by the MIT copyright statement with an acknowledgment to CERN.¹⁷

The main web servers over time

NCSA httpd and Apache

In February 1995 the most popular server on the web was the NCSA HTTP daemon, written by Rob McCool at NCSA at the University of Illinois at Urbana-Champaign. Development had stalled after McCool left NCSA in mid-1994, and webmasters were passing around their own fixes.¹⁸

By the end of February 1995, eight of those webmasters had formed the Apache Group. Starting from NCSA httpd 1.3, they released Apache 0.6.2 in April 1995 and Apache 1.0 on December 1, 1995.¹⁸ Less than a year after the group formed, Apache passed NCSA’s server as the most used on the internet, according to the 1996 Netcraft survey cited by the project.¹⁸

Netcraft has published a monthly web server survey since 1995.¹⁹ In a post looking back on the survey’s first year, it reported that the number of sites had grown from 10,835 in August 1995 to 62,430, that NCSA’s share had fallen from 57% to 18%, and that Apache now ran more than one in three sites. Netscape‘s server share peaked at 17% in March 1996.²⁰

The Apache HTTP Server is still maintained. Version 2.4.69 came out on October 1, 2026.²¹ Its HTTP/2 support, the mod_http2 module, has been available since version 2.4.17.²²

Microsoft IIS

On February 12, 1996, Microsoft made Internet Information Server (IIS), its web server for Windows NT Server, available as a free download. Its announcement claimed IIS ran more than four times faster than Netscape’s Netsite server for Windows NT.²³ In the same look back, Netcraft put IIS at 5.5% of its survey, from a standing start in February 1996.²⁰

Windows NT Server 4.0, announced on July 31, 1996, included IIS version 2.0.²⁴ A Microsoft Learn page first published in 2016 calls IIS 10.0, which shipped with Windows 10 and Windows Server 2016, the latest version of IIS.²⁵ As of October 22, 2026, W3Techs finds IIS on 2.9% of websites with a known server, and version 10 on 86.2% of those.²⁶ Like Apache’s .htaccess files, IIS can read settings from web.config files inside a site’s folders.²⁷

Nginx

Igor Sysoev began writing Nginx in the spring of 2002 to solve the C10k problem, handling 10,000 connections at once on one server. He released it as open source on October 4, 2004. A 2022 post on the NGINX blog, run by F5, says Nginx became the most widely used web server in the world in 2021.²⁸ Nginx has offered HTTP/3 since version 1.25.0, though as of October 22, 2026 its documentation still calls the module experimental and says it is not built by default.²⁹

LiteSpeed

LiteSpeed Technologies was founded in New Jersey in 2002. It launched LiteSpeed Web Server in 2003 and released a free, open-source edition, OpenLiteSpeed, in 2013.³⁰ The company sells its server as a drop-in replacement for Apache: it reads Apache configuration files and .htaccess files directly, uses an event-driven design and works with hosting control panels such as cPanel, Plesk and DirectAdmin.³¹ It also says it was the first to ship a production-ready implementation of HTTP/3.³¹

Newer names

• OpenResty is an open-source web platform that combines an enhanced Nginx core with LuaJIT, a just-in-time compiler for the Lua language.³²
• Caddy says it was the first web server to use HTTPS automatically and by default. It gets certificates from Let’s Encrypt and, if that fails, from ZeroSSL.³³
• Cloudflare Server is described by W3Techs as a web server developed by Cloudflare.³⁴ Cloudflare’s network works as a reverse proxy, a server that sits in front of one or more web servers and intercepts requests from visitors.³⁵ RFC 9110 defines a reverse proxy as an intermediary that acts as the origin server for the visitor’s connection.²

Market share today

Two surveys, W3Techs and Netcraft, measure different things, so their numbers do not match. W3Techs reports the share of websites whose web server it can identify. Its sample is more than 20 million sites that it judges to have meaningful content, and it counts each website once, not each page or subdomain.³⁶ As of October 22, 2026, its figures are:¹³

W3Techs notes that one website can use more than one web server, so its percentages add up to more than 100%.¹³ A site behind a reverse proxy, for example, is answered by the proxy while another server holds the site itself.³⁵ On September 22, 2026, W3Techs reported that Cloudflare Server had overtaken Nginx as the most used web server in its survey.³⁷

Netcraft instead counts every site that answers its survey, about 1.5 billion, and reports shares by the developer of the server software, separately for sites, domains and web-facing computers. Its July 2026 survey, published on July 27, 2026, and still the latest it had released as of October 22, 2026, covered 1,494,915,628 sites, 305,348,459 domains and 14,772,048 computers.³⁸ In it:³⁸

• All sites: nginx 20.37%, Cloudflare 16.67%, Apache 11.50% and OpenResty 8.02%.
• Top million busiest sites: Cloudflare 28.29%, nginx 20.02%, Apache 15.56% and LiteSpeed 3.88%.
• Computers: nginx 43.92%, Apache 18.82% and Microsoft 5.73%.

The gap for LiteSpeed shows how much method matters: W3Techs finds it on 13.9% of websites with a known server, while Netcraft places it at 3.88% of the million busiest sites.³⁹³⁸ The two figures do not contradict each other: W3Techs counts a filtered sample of websites, while Netcraft ranks the busiest million sites within a much larger count.

Timeline

1. October 1, 2026Apache HTTP Server 2.4.69 is released²¹
2. September 22, 2026W3Techs reports that Cloudflare Server has overtaken Nginx³⁷
3. 2013LiteSpeed releases the open-source OpenLiteSpeed³⁰
4. October 4, 2004Igor Sysoev releases Nginx as open source²⁸
5. 2003LiteSpeed Web Server is launched³⁰
6. July 31, 1996Windows NT Server 4.0 is announced, including IIS 2.0²⁴
7. July 15, 1996CERN httpd 3.0A, the final version, is generated¹⁷
8. February 12, 1996Microsoft makes Internet Information Server a free download²³
9. December 1, 1995Apache 1.0 is released¹⁸
10. August 1995Netcraft's survey counts 10,835 sites²⁰
11. April 1995Apache 0.6.2, the first public release, comes out¹⁸
12. February 11, 1994CERN httpd 2.15beta fully implements CGI/1.0¹¹
13. December 12, 1991Paul Kunz sets up the first web server outside Europe, at SLAC¹⁵
14. June 1991CERN httpd version 0.1 appears in the server's change history¹¹
15. 1990The first web server is running at CERN by the end of the year¹⁴

What it means for your website

See also

• HTTP
• Apache HTTP Server
• Nginx
• Web hosting
• The first website (1991)
• Web hosting
• How does a website work
• Data center

References

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35. What is a reverse proxy?. Cloudflare Learning Center. accessed October 22, 2026.
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Web Building Encyclopedia. First published October 22, 2026. Last reviewed October 22, 2026. Every fact on this page is linked to a source we opened. Spotted an error? Write to [email protected].