Everything about Internet Explorer totally explained
Windows Internet Explorer (formerly
Microsoft Internet Explorer abbreviated
MSIE), commonly abbreviated to
IE, is a series of
graphical web browsers developed by
Microsoft and included as part of the
Microsoft Windows line of
operating systems starting in 1995. It has been the
most widely used web browser since 1999, attaining a peak of about 95%
usage share during 2002 and 2003 with
IE5 and
6 but steadily declining since, despite the introduction of
IE7. Microsoft spent over a 100 million dollars (
USD) a year in the late 1990s, with over 1000 people working on IE by 1999.
Internet Explorer was first released as part of the add-on package
Plus! for Windows 95. Later versions were available as free downloads, or in service packs, and included in the
OEM service releases of Windows 95 and later versions of Windows. The most recent stable release is version
7.0, which is available as a free update for
Windows XP Service Pack 2, and
Windows Server 2003 with Service Pack 1 or later,
Windows Vista, and
Windows Server 2008. An embedded OEM version called Internet Explorer for Windows CE (IE CE) is also available for WinCE based platforms and is currently based on IE6. Another
Windows CE/
Windows Mobile browser known as
Internet Explorer Mobile is from a different code base and shouldn't be confused with desktop versions of the browser. In early 2008, a
beta for the next version
Internet Explorer 8 was released to the public.
History
The Internet Explorer project was started in the summer of 1994 by Thomas Reardon and subsequently led by Benjamin Slivka, leveraging source code from
Spyglass, Inc. Mosaic, an early commercial web browser with formal ties to the pioneering
NCSA Mosaic browser. In late 1994,
Microsoft licensed Spyglass Mosaic for a quarterly fee plus a percentage of Microsoft's non-Windows revenues for the software. Although bearing a name similar to
NCSA Mosaic, which was the first widely used web browser, Spyglass Mosaic was relatively unknown in its day and used the NCSA Mosaic source code only sparingly.
Internet Explorer for Mac and
Internet Explorer for UNIX (the latter for use through the
X Window System on
Solaris and
HP-UX), and versions for many older versions of Windows have been discontinued, and are no longer available from Microsoft. Only supported Windows, and Windows Mobile versions remain in active development.
Version 1
Version 1, released in
August 1995 was a modified version of Spyglass Mosaic. It came with
Microsoft Plus! for
Windows 95 and OEM release of Windows 95. It was installed as part of the
Internet Jumpstart Kit in Plus!.
Version 1.5 was released several months later for Windows NT and added support for basic table rendering. The Internet Explorer team began with about half a dozen people in early development.
Version 2
Internet Explorer 2.0 was released for Windows 95,
Windows NT 3.5, and
NT 4.0 in November 1995 (following a 2.0 beta in October). It featured support for SSL, cookies,
VRML,
RSA, and
Internet newsgroups. Version 2 was also the first release for
Windows 3.1 and Macintosh
System 7.0.1(PPC or 68k), although the Mac version wasn't released until January 1996 for PPC, and April for 68k. Version 2.1 for the Mac came out in August of 1996, although by this time Windows was getting 3.0. Version 2 was included in Windows 95 OSR 1 and Microsoft's
Internet Starter Kit for Windows 95 in early 1996, It launched with twelve languages including English but this expanded to 24, 20, and 9 for Win 95, Win 3.1 and Mac respectively by April 1996. The 2.0i version supported double-byte character-set. The Internet Explorer team consisted of roughly 100 people during the development of three months.
Version 5
Internet Explorer 5, launched on
March 18,
1999, and subsequently included with
Windows 98 Second Edition and bundled with
Office 2000, was another significant release that supported
bi-directional text,
ruby characters,
XML,
XSL and the ability to save web pages in
MHTML format. IE5 was bundled with
Outlook Express 5. Also, with the release of Internet Explorer 5.0, Microsoft released the first version of
XMLHttpRequest, giving birth to
Ajax (even though the term "Ajax" wasn't coined until years later.) It was the last with a 16-bit version.
Internet Explorer 5.01, a bug fix version, was released in
December 1999.
Windows 2000 includes this version.
Internet Explorer 5.5 followed in July 2000, improving its print preview capabilities, CSS and HTML standards support, and developer APIs; this version was bundled with
Windows Me. Version 5.5 also included support for 128-bit encryption. However, Version 5 was the last version for
Mac and
UNIX. Version 5.5 was the last to have
Compatibility Mode, which allowed
Internet Explorer 4 to be run side by side with the 5.x. The IE team consisted of over 1000 people by 1999, with funding on the order of 100 million
USD per year.
Version 6
Internet Explorer 6.0 was released on
August 27,
2001, a few months before Windows XP. This version included DHTML enhancements, content restricted inline frames, and partial support of CSS level 1,
DOM level 1 and
SMIL 2.0. The
MSXML engine was also updated to version 3.0. Other new features included a new version of the
Internet Explorer Administration Kit (IEAK), Media bar,
Windows Messenger integration, fault collection, automatic image resizing,
P3P, and a new look-and-feel that was in line with the "Luna" visual style of Windows XP, when used in Windows XP.
6.0 SP1 offered several security enhancements and coincided with XP SP1 patch release. In 2002, the
Gopher protocol was disabled and support for it was dropped in Internet Explorer 7.
6.0 SV1 ('6 SP2') came out
August 6 2004 for
Windows XP SP2 and offered various security enhancements and new color buttons on the user interface. IE6 updated the original 'blue e' logo to a lighter blue and more
3-d look. It includes bug fixes, enhancements to its support for web standards,
tabbed browsing with tab preview and management, a multiple-engine search box, a web feeds reader,
Internationalized Domain Name support (IDN), and antiphishing filter. With IE7, Internet Explorer has been decoupled from the Windows Shell - unlike previous versions, the Internet Explorer
ActiveX control isn't hosted in the Windows Explorer process, but rather runs in a separate Internet Explorer process. On
October 5,
2007,
Microsoft removed the 'genuine software' validation before install, which means that all versions of Windows, whether able to pass validation or not, are able to install the
browser.
Version 8
Internet Explorer 8 is the latest version of Internet Explorer and has been in development since August 2007 at the latest. On March 5, 2008, the first public beta (Beta 1) was released to the general public. It supports
Windows XP SP2 and SP3,
Windows Server 2003 SP2,
Windows Vista and
Windows Server 2008 on both 32-bit as well as 64-bit architectures.
Security, ease of use, and improvements in
RSS,
CSS, and
Ajax support are Microsoft's priorities for IE8. It includes much stricter compliance with
web standards, including a planned full
Cascading Style Sheets 2.1 compliance for the release version. All these changes allow Internet Explorer 8 to pass the
Acid2 test. However, to prevent compatibility issues, IE8 also includes the IE7 rendering behavior. Sites that expect IE7 quirks can disable the IE8's breaking changes by including a
meta element.
IE8 also includes numerous improvements to
JavaScript support as well as performance improvements.
Standards support
Internet Explorer, using the
Trident layout engine, almost fully supports
HTML 4.01,
CSS Level 1,
XML 1.0 and
DOM Level 1, with minor implementation gaps. It partially supports CSS Level 2 and DOM Level 2, with major implementation gaps and conformance issues. Full conformance to the CSS 2.1 specification is on the agenda for the final
Internet Explorer 8 release. It has no support for XHTML, though it can render XHTML documents authored with HTML compatibility principles and served with a
text/html MIME-type.
Internet Explorer uses
DOCTYPE sniffing to choose between "
quirks mode" (renders similarly to older versions of MSIE) and
standards mode (renders closer to W3C's specifications) for HTML and CSS rendering on screen (for printing Internet Explorer always uses standards mode). It fully supports
XSLT 1.0 or the December 1998 Working Draft of
XSL, depending on the version of
MSXML (a
dynamic link library) available. It also provides its own dialect of
ECMAScript called
JScript.
Internet Explorer has been subjected to criticism over its limited support for
open web standards and a major goal of Internet Explorer 8 is to improve support for such standards.
Proprietary features
Internet Explorer has introduced an array of proprietary extensions to many of the standards, including HTML, CSS and the DOM. This has resulted in a number of web pages that can only be viewed properly using Internet Explorer. Some view this as an example of what is called “
embrace, extend and extinguish” (EEE), a way to drive competitors out of business by forcing them to use proprietary technology that Microsoft controls, resulting in
vendor lock-in.
Internet Explorer has introduced a number of extensions to JScript which have been adopted by other browsers. These include the innerHTML property, which returns the HTML string within an element; the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response; and the designMode attribute of the contentDocument object, which enables rich text editing of HTML documents. Some of these functionalities were not possible until the introduction of the W3C DOM methods. Its
Ruby character extension to HTML is also accepted as a module in W3C XHTML 1.1, though it isn't found in all versions of W3C HTML.
The
favicon (short for "favorites icon") introduced by Internet Explorer is now also supported and extended in other browsers. It allows web pages to specify a 16-by-16 pixel image for use in bookmarks. Originally, support was provided only for the native Windows ICO format, however it has now been extended to other types of images such as PNG and GIF.
Microsoft submitted several other features of IE for consideration by the W3C for standardization. These include the 'behavior' CSS property, which connects the HTML elements with JScript behaviors (known as HTML Components, HTC);
HTML+TIME profile, which adds timing and media synchronization support to HTML documents (similar to the W3C
XHTML+SMIL); and the
VML vector graphics file format. However, all were rejected, at least in their original forms. VML was, however, subsequently combined with
PGML (proposed by
Adobe and
Sun), resulting in the W3C-approved
SVG format, currently one of the few vector image formats being used on the web.
Other proprietary standards include:
- Support for vertical text, but in a syntax different from W3C CSS3 candidate recommendation.
- Support for a variety of image effects and page transitions, which are not found in W3C CSS.
- Support for obfuscated script code, in particular
JScript.Encode.
- Support for embedding EOT fonts in web pages.
Usability and accessibility
Internet Explorer makes use of the accessibility framework provided in Windows. Internet Explorer is also a user interface for FTP, with operations similar to that of Windows Explorer (although this feature requires a shell window to be opened in recent versions of the browser, rather than natively within the browser).
Visual Basic for Applications (VBA) isn't supported, but available via extension (iMacros). Recent versions feature
pop-up blocking and
tabbed browsing.
Tabbed browsing can also be added to older versions by installing Microsoft's
MSN Search Toolbar or Yahoo's
Yahoo Toolbar.
Cache
Internet Explorer caches visited content in the
Temporary Internet Files folder to allow quicker access (or offline access) to previously visited pages. The content is indexed in a database file, known as
Index.dat. Multiple
Index.dat files exist which index different content - visited content,
web feeds, autocomplete entries, visited
URLs, cookies etc.
Prior to IE7, clearing the cache used to clear the index but the files themselves were not removed. This feature can be a potential security risk for both individuals and companies. IE7 on, both the entries as well as the files themselves are removed.
Security
Internet Explorer uses a zone-based
security framework that groups sites based on certain conditions, including whether it's an Internet- or intranet-based site as well as a user-editable whitelist. Security restrictions are applied per zone; all the sites in a zone are subject to the restrictions.
Internet Explorer 6 SP2 onwards uses the
Attachment Execution Service of
Microsoft Windows to mark executable files downloaded from the Internet as being potentially unsafe. Accessing files marked as such will prompt the user to make an explicit trust decision to execute the file, as executables originating from the Internet can be potentially unsafe. This helps in preventing accidental installation of malware.
Internet Explorer 7 introduced the phishing filter, that restricts access to
phishing sites unless the user overrides the decision. With version 8, it also blocks access to sites known to host
malware. Downloads are also checked to see if they're known to be malware-infected.
In
Windows Vista, Internet Explorer can optionally run in what is called
Protected Mode, where the privileges of the browser itself is severely restricted - it can't make any system-wide changes. This also effectively restricts the privileges of any add-ons. As a result, even if the browser or any add-on is compromised, the damage the security breach can cause is limited.
Patches and updates to the browser are released periodically and made available through the Windows Update service, as well as through
Automatic Updates. Although security patches continue to be released for a range of platforms, most recent feature additions and security improvements are released for
Windows XP only.
Group Policy
Internet Explorer is fully configurable using
Group Policy. Administrators of
Windows Server domains can apply and enforce a variety of settings that affect the user interface (such as disabling menu items and individual configuration options), as well as underlying security features such as downloading of files, zone configuration, per-site settings, ActiveX control behavior, and others. Policy settings can be configured for each user and for each machine. Internet Explorer also supports
Integrated Windows Authentication.
Architecture
Internet Explorer uses a
componentized architecture built around the
Component Object Model (COM) technology. It is made up of five major components, each of which are contained in a separate
.dll and expose a set of COM
interface that enables them to be hosted by the Internet Explorer main executable,
iexplore.exe:
WinInet.dll: WinInet.dll is the protocol handler for HTTP and FTP. It handles all network communication over these protocols.
;URlMon.dll: URLMon.dll is responsible for MIME-type handling and download of web content.
MSHTML.dll: MSHTML.dll houses the Trident rendering engine introduced in Internet Explorer 4, which is responsible for displaying the pages on-screen and handling the Document Object Model of the web pages. MSHTML.dll parses the HTML/CSS file and creates the internal DOM tree representation of it. It also exposes a set of APIs for runtime inspection and modification of the DOM tree. The DOM tree is further processed by a layout engine which then renders the internal representation on screen. » Internet Explorer doesn't include any scripting functionality natively. Rather MSHTML.dll exposes another set of APIs that allow any scripting environment to be plugged-in and access the DOM tree. Internet Explorer 8 includes the bindings for the Active Scripting engine (which is a part of Microsoft Windows) is provided, which allows any language implemented as an Active Scripting module to be used for client-side scripting. By default, only the JScript and VBScript modules are provided; third party implementations like ScreamingMonkey (for ECMAScript 4 support) can also be used. Microsoft also makes available the Microsoft Silverlight runtime that allows CLI languages, including DLR-based dynamic languages like IronPython and IronRuby, to be used for client-side scripting.
;ShDocVw.dll: ShDocVw.dll provides the navigation, local caching and history functionalities for the browser.
BrowseUI.dll: BrowseUI.dll is responsible for the browser user interface, including the browser chrome, which houses all the menus and toolbars.
Internet Explorer 8 introduces some major architectural changes, called Loosely Coupled IE (LCIE). LCIE separates the UI processes from the process hosting the different web applications in different tabs (tab processes). An UI process can create multiple tab processes, each of which can be of a different integrity level; each tab process can host multiple web sites. Each tab process has its own cookie cache. The two processes use asynchronous Inter-Process Communication to synchronize themselves. Generally, there will be a single tab process for all web sites. In Windows Vista with protected mode turned on, however, opening privileged content (such as local HTML pages) will create a new tab process as it will
not be constrained by protected mode of operation.
Extensibility
Internet Explorer also exposes a set of
Component Object Model (COM) interfaces that allow other components to extend the functionality of the browser.
While Internet Explorer isn't alone in having exploitable vulnerabilities, its ubiquity has resulted in many more affected computers when vulnerabilities are found. Microsoft hasn't responded as quickly as competitors in fixing security holes and making patches available, in some cases giving malicious web site operators months to exploit them before Microsoft releases a patch.
Market adoption
Usage Share
| Internet Explorer, All Versions |
75.47% |
| Internet Explorer 4 |
0.01% |
| Internet Explorer 5.0 |
0.11% |
| Internet Explorer 5.5 |
0.11% |
| Internet Explorer 6 |
32.30% |
| Internet Explorer 7 |
42.93% |
The adoption rate of Internet Explorer seems to be closely related to that of Microsoft Windows, as it's the default web browser that comes with Windows. Since the integration of Internet Explorer 2.0 with Windows 95 OSR 1 in 1996, and especially after version 4.0's release, the adoption was greatly accelerated: from below 20% in 1996 to about 40% in 1998 and over 80% in 2000. This effect, however, has recently been dubbed the "Microsoft
monoculture", by analogy to the problems associated with lack of
biodiversity in an
ecosystem. By 2002, Internet Explorer had almost completely superseded its main rival
Netscape and dominated the market.
A CNN article noted at the release of
Internet Explorer 4,
"Microsoft's Internet Explorer has made inroads and various estimates put its share of the browser market 30 to 35 percent from about 10 percent a year ago."
After having fought and won the browser wars of the late 1990s, Internet Explorer began to see its usage share shrink. Having attained a peak of about 95% during 2002 and 2003, it has since been in a slow, steady decline, due to the adoption of
Mozilla Firefox, which statistics indicate is currently the most significant competition. Nevertheless, Internet Explorer remains the dominant web browser, with a global usage share of around 75% (though measurements vary). Usage is higher in Asia and lower in Europe.
Firefox 1.0 had surpassed
Internet Explorer 5 in early 2005 with Firefox 1.0 at roughly 8 percent market share.
An article notes at the release of
Internet Explorer 7 in October 2006,
"IE6 had the lion's share of the browser market with 77.22%. Internet Explorer 7 had climbed to 3.18%, while Firefox 2.0 was at 0.69%." Internet Explorer 7 was released at the same time as Firefox 2.0, and overtook Firefox 1.x by November 2006, at roughly 9% market share. Firefox 2.0 had overtaken 1.x by January 2007,, but IE7 didn't surpass
IE6 until December 2007. By January 2008, their respective version market share stood at 43% IE7, 32% IE6, 16% FF2, 4%
SF 3, and both FF1.x and IE5 versions at less than half a percent.
Market share by year and version
Approximate usage over time based on various usage share counters averaged for the year overall, or for the fourth quarter, or for the last month in the year depending on availability of reference.
Further Information
Get more info on 'Internet Explorer'.
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