Microsoft Excel

Microsoft Excel is a spreadsheet application developed by Microsoft for Microsoft Windows and Mac OS. It features calculation, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications. It has been a very widely applied spreadsheet for these platforms, especially since version 5 in 1993, and it has replaced Lotus 1-2-3 as the industry standard for spreadsheets. Excel forms part of Microsoft Office.

Basic operation
Microsoft Excel has the basic features of all spreadsheets, using a grid of cells arranged in numbered rows and letter-named columns to organize data manipulations like arithmetic operations. It has a battery of supplied functions to answer statistical, engineering and financial needs. In addition, it can display data as line graphs, histograms and charts, and with a very limited three-dimensional graphical display. It allows sectioning of data to view its dependencies on various factors for different perspectives (using pivot tables and the scenario manager). It has a programming aspect, Visual Basic for Applications, allowing the user to employ a wide variety of numerical methods, for example, for solving differential equations of mathematical physics, and then reporting the results back to the spreadsheet. It also has a variety of interactive features allowing user interfaces that can completely hide the spreadsheet from the user, so the spreadsheet presents itself as a so-called application, or decision support system (DSS), via a custom-designed user interface, for example, a stock analyzer, or in general, as a design tool that asks the user questions and provides answers and reports. In a more elaborate realization, an Excel application can automatically poll external databases and measuring instruments using an update schedule, analyze the results, make a Word report or Power Point slide show, and e-mail these presentations on a regular basis to a list of participants.

Microsoft allows for a number of optional command-line switches to control the manner in which Excel starts.

VBA programming
The Windows version of Excel supports programming through Microsoft's Visual Basic for Applications (VBA), which is a dialect of Visual Basic. Programming with VBA allows spreadsheet manipulation that is awkward or impossible with standard spreadsheet techniques. Programmers may write code directly using the Visual Basic Editor (VBE), which includes a window for writing code, debugging code, and code module organization environment. The user can implement numerical methods as well as automating tasks such as formatting or data organization in VBA and guide the calculation using any desired intermediate results reported back to the spreadsheet.

VBA was removed from Mac Excel 2008, as the developers did not believe that a timely release would allow porting the VBA engine natively to Mac OS X. VBA was restored in the next version, Mac Excel 2011.

A common and easy way to generate VBA code is by using the Macro Recorder. The Macro Recorder records actions of the user and generates VBA code in the form of a macro. These actions can then be repeated automatically by running the macro. The macros can also be linked to different trigger types like keyboard shortcuts, a command button or a graphic. The actions in the macro can be executed from these trigger types or from the generic toolbar options. The VBA code of the macro can also be edited in the VBE. Certain features such as loop functions and screen prompts by their own properties, and some graphical display items, cannot be recorded, but must be entered into the VBA module directly by the programmer. Advanced users can employ user prompts to create an interactive program, or react to events such as sheets being loaded or changed.

Users should be aware that using Macro Recorded code may not be compatible from one version of Excel to another. Some code that is used in Excel 2010 can not be used in Excel 2003. Making a Macro that changes the cell colors and making changes to other aspects of cells may not be backward compatible.

VBA code interacts with the spreadsheet through the Excel Object Model, a vocabulary identifying spreadsheet objects, and a set of supplied functions or methods that enable reading and writing to the spreadsheet and interaction with its users (for example, through custom toolbars or command bars and message boxes). User-created VBA subroutines execute these actions and operate like macros generated using the macro recorder, but are more flexible and efficient.

History
From its first version Excel supported end user programming of macros (automation of repetitive tasks) and user defined functions (extension of Excel's built-in function library). In early versions of Excel these programs were written in a macro language whose statements had formula syntax and resided in the cells of special purpose macro sheets (stored with file extension .XLM in Windows.) XLM was the default macro language for Excel through Excel 4.0. Beginning with version 5.0 Excel recorded macros in VBA by default but with version 5.0 XLM recording was still allowed as an option. After version 5.0 that option was discontinued. All versions of Excel, including Excel 2010 are capable of running an XLM macro, though Microsoft discourages their use.

Charts
Excel supports charts, graphs, or histograms generated from specified groups of cells. The generated graphic component can either be embedded within the current sheet, or added as a separate object.

These displays are dynamically updated if the content of cells change. For example, suppose that the important design requirements are displayed visually; then, in response to a user's change in trial values for parameters, the curves describing the design change shape, and their points of intersection shift, assisting the selection of the best design.

Number of rows and columns
Versions of Excel up to 7.0 had a limitation in the size of their data sets of 16K (214 = 16384) rows. Versions 8.0 through 11.0 could handle 64K (216 = 65536) rows and 256 columns (28 as label 'IV'). Version 12.0 can handle 1M (220 = 1048576) rows, and 16384 (214 as label 'XFD') columns.

File formats
Microsoft Excel up until 2007 version used a proprietary binary file format called Excel Binary File Format (.XLS) as its primary format. Excel 2007 uses Office Open XML as its primary file format, an XML-based format that followed after a previous XML-based format called "XML Spreadsheet" ("XMLSS"), first introduced in Excel 2002.

Although supporting and encouraging the use of new XML-based formats as replacements, Excel 2007 remained backwards-compatible with the traditional, binary formats. In addition, most versions of Microsoft Excel can read CSV, DBF, SYLK, DIF, and other legacy formats. Support for some older file formats was removed in Excel 2007. The file formats were mainly from DOS-based programs.

Binary
OpenOffice.org has created documentation of the Excel format. Since then Microsoft made the Excel binary format specification available to freely download.

XML Spreadsheet
The XML Spreadsheet format introduced in Excel 2002 is a simple, XML based format missing some more advanced features like storage of VBA macros. Though the intended file extension for this format is .xml, the program also correctly handles XML files with .xls extension. This feature is widely used by third-party applications (e.g. MySQL Query Browser) to offer "export to Excel" capabilities without implementing binary file format. The following example will be correctly opened by Excel if saved either as Book1.xml or Book1.xls:

            

Current file extensions
Microsoft Excel 2007, along with the other products in the Microsoft Office 2007 suite, introduced new file formats. The first of these (.xlsx) is defined in the Office Open XML (OOXML) specification.

Using other Windows applications
Windows applications such as Microsoft Access and Microsoft Word, as well as Excel can communicate with each other and use each other's capabilities. The most common are Dynamic Data Exchange: although strongly deprecated by Microsoft, this is a common method to send data between applications running on Windows, with official MS publications referring to it as "the protocol from hell". As the name suggests, it allows applications to supply data to others for calculation and display. It is very common in financial markets, being used to connect to important financial data services such as Bloomberg and Reuters.

OLE Object Linking and Embedding: allows a Windows application to control another to enable it to format or calculate data. This may take on the form of "embedding" where an application uses another to handle a task that it is more suited to, for example a Powerpoint presentation may be embedded in an Excel spreadsheet or vice versa.

Using external data
Excel users can access external data sources via Microsoft Office features such as (for example)  connections built with the Office Data Connection file format. Excel files themselves may be updated using a Microsoft supplied ODBC driver.

Excel can accept data in real time through several programming interfaces, which allow it to communicate with many data sources such as Bloomberg and Reuters (through addins such as Power Plus Pro).
 * DDE : "Dynamic Data Exchange" uses the message passing mechanism in Windows to allow data to flow between Excel and other applications. Although it is easy for users to create such links, programming such links reliably is so difficult that Microsoft, the creators of the system, officially refer to it as "the protocol from hell". In spite of its many issues DDE remains the most common way for data to reach traders in financial markets.
 * Network DDE Extended the protocol to allow spreadsheets on different computers to exchange data. Given the view above, it is not surprising that in Vista, Microsoft no longer supports the facility.
 * Real Time Data : RTD although in many ways technically superior to DDE, has been slow to gain acceptance, since it requires non-trivial programming skills, and when first released was neither adequately documented nor supported by the major data vendors.

Alternatively, Microsoft Query provides ODBC-based browsing within Microsoft Excel.

Export and migration of spreadsheets
Programmers have produced APIs to open Excel spreadsheets in a variety of applications and environments other than Microsoft Excel. These include opening Excel documents on the web using either ActiveX controls, or plugins like the Adobe Flash Player. The Apache POI opensource project provides Java libraries for reading and writing Excel spreadsheet files. ExcelPackage is another open-source project that provides server-side generation of Microsoft Excel 2007 spreadsheets. PHPExcel is a PHP library that converts Excel5, Excel 2003, and Excel 2007 formats into objects for reading and writing within a web application. Excel Services is a current .NET developer tool that can enhance Excel's capabilities. Excel spreadsheets can be accessed from Python with DataNitro, PyXLL or the COM interface.

Password protection
Microsoft Excel protection offers several types of passwords: All passwords except password to open a document can be removed instantly regardless of Microsoft Excel version used to create the document. These types of passwords are used primarily for shared work on a document. Such password-protected documents are not encrypted, and a data sources from a set password is saved in a document’s header. Password to protect workbook is an exception – when it is set, a document is encrypted with the standard password “VelvetSweatshop”, but since it is known to public, it actually does not add any extra protection to the document. The only type of password that can prevent a trespasser from gaining access to a document is password to open a document. The cryptographic strength of this kind of protection depends strongly on the Microsoft Excel version that was used to create the document.
 * password to open a document
 * password to modify a document
 * password to unprotect worksheet
 * password to protect workbook
 * password to protect the sharing workbook

In Microsoft Excel 95 and earlier versions, password to open is converted to a 16-bit key that can be instantly cracked. In Excel 97/2000 the password is converted to a 40-bit key, which can also be cracked very quickly using modern equipment. As regards services which use rainbow tables (e.g. Password-Find), it takes up to several seconds to remove protection. In addition, password-cracking programs can brute-force attack passwords at a rate of hundreds of thousands of passwords a second, which not only lets them decrypt a document, but also find the original password.

In Excel 2003/XP the encryption is slightly better – a user can choose any encryption algorithm that is available in the system (see Cryptographic Service Provider). Due to the CSP, an Excel file can't be decrypted, and thus the password to open can't be removed, though the brute-force attack speed remains quite high. Nevertheless, the older Excel 97/2000 algorithm is set by the default. Therefore, users who did not changed the default settings lack reliable protection of their documents.

The situation changed fundamentally in Excel 2007, where the modern AES algorithm with a key of 128 bits started being used for decryption, and a 50,000-fold use of the hash function SHA1 reduced the speed of brute-force attacks down to hundreds of passwords per second. In Excel 2010, the strength of the protection by the default was increased two times due to the use of a 100,000-fold SHA1 to convert a password to a key.

Quirks
Other errors specific to Excel include misleading statistics functions, mod function errors, date limitations and the Excel 2007 error.

Statistical functions
The accuracy and convenience of statistical tools in Excel has been criticized,   as mishandling missing data, as returning incorrect values due to inept handling of round-off and large numbers, as only selectively updating calculations on a spreadsheet when some cell values are changed, and as having a limited set of statistical tools. Microsoft has announced some of these issues are addressed in Excel 2010.

Excel MOD function error
Excel has issues with modulo operations. In the case of excessively large results, Excel will return the error warning #NUM! instead of an answer.

Date problems
Excel includes January 0, 1900 and February 29, 1900, incorrectly treating 1900 as a leap year. The bug originated from Lotus 1-2-3, and was purposely implemented in Excel for the purpose of backward compatibility. This legacy has later been carried over into Office Open XML file format. Excel also does not support dates before 1900.

Filenames
Microsoft Excel will not open two documents with the same name and instead will display the following error:
 * A document with the name '%s' is already open. You cannot open two documents with the same name, even if the documents are in different folders. To open the second document, either close the document that is currently open, or rename one of the documents.

The reason is for calculation ambiguity with linked cells. If there is a cell ='[Book1.xlsx]Sheet1'!$G$33, and there are two books named "Book1" open, there is no way to tell which one the user means.

Numeric precision


Despite the use of 15-figure precision, Excel can display many more figures (up to thirty) upon user request. But the displayed figures are not those actually used in its computations, and so, for example, the difference of two numbers may differ from the difference of their displayed values. Although such departures are usually beyond the 15th decimal, exceptions do occur, especially for very large or very small numbers. Serious errors can occur if decisions are made based upon automated comparisons of numbers (for example, using the Excel If function), as equality of two numbers can be unpredictable.

In the figure the fraction 1/9000 is displayed in Excel. Although this number has a decimal representation that is an infinite string of ones, Excel displays only the leading 15 figures. In the second line, the number one is added to the fraction, and again Excel displays only 15 figures. In the third line, one is subtracted from the sum using Excel. Because the sum in the second line has only eleven 1's after the decimal, the difference when 1 is subtracted from this displayed value is three 0's followed by a string of eleven 1's. However, the difference reported by Excel in the third line is three 0's followed by a string of thirteen 1's and two extra erroneous digits. This is because Excel calculates with about half a digit more than it displays.

Excel works with a modified 1985 version of the IEEE 754 specification. Excel's implementation involves conversions between binary and decimal representations, leading to accuracy that is on average better than one would expect from simple fifteen digit precision, but that can be worse. See the main article for details.

Besides accuracy in user computations, the question of accuracy in Excel-provided functions may be raised. Particularly in the arena of statistical functions, Excel has been criticized for sacrificing accuracy for speed of calculation.

As many calculations in Excel are executed using VBA, an additional issue is the accuracy of VBA, which varies with variable type and user-requested precision.

Early History
Microsoft originally marketed a spreadsheet program called Multiplan in 1982. Multiplan became very popular on CP/M systems, but on MS-DOS systems it lost popularity to Lotus 1-2-3. Microsoft released the first version of Excel for the Macintosh on September 30, 1985, and the first Windows version was 2.05 (to synchronize with the Macintosh version 2.2) in November 1987. Lotus was slow to bring 1-2-3 to Windows and by 1988 Excel had started to outsell 1-2-3 and helped Microsoft achieve the position of leading PC software developer. This accomplishment, dethroning the king of the software world, solidified Microsoft as a valid competitor and showed its future of developing GUI software. Microsoft pushed its advantage with regular new releases, every two years or so.

Microsoft Windows
Excel 1.0 was not released for Windows or MS-DOS. As a result, Excel 2.0 for Windows is the first version of Excel for Intel platform.

Excel 2.0 for Windows (1987)
The first Windows version was labeled "2" to correspond to the Mac version. This included a run-time version of Windows.

Excel 3.0 (1990)
Included toolbars, drawing capabilities, outlining, add-in support, 3D charts, and many more new features.

Excel 4.0 (1992)
Introduced auto-fill.

Also, an easter egg in Excel 4.0 reveals a hidden animation of a dancing set of numbers 1 through 3, representing Lotus 1-2-3, which was then crushed by an Excel logo.

Excel 5.0 (1993)
With version 5.0, Excel has included Visual Basic for Applications (VBA), a programming language based on Visual Basic which adds the ability to automate tasks in Excel and to provide user-defined functions (UDF) for use in worksheets. VBA is a powerful addition to the application and includes a fully featured integrated development environment (IDE). Macro recording can produce VBA code replicating user actions, thus allowing simple automation of regular tasks. VBA allows the creation of forms and in‑worksheet controls to communicate with the user. The language supports use (but not creation) of ActiveX (COM) DLL's; later versions add support for class modules allowing the use of basic object-oriented programming techniques.

The automation functionality provided by VBA made Excel a target for macro viruses. This caused serious problems until antivirus products began to detect these viruses. Microsoft belatedly took steps to prevent the misuse by adding the ability to disable macros completely, to enable macros when opening a workbook or to trust all macros signed using a trusted certificate.

Versions 5.0 to 9.0 of Excel contain various Easter eggs, including a "Hall of Tortured Souls", although since version 10 Microsoft has taken measures to eliminate such undocumented features from their products.

Excel 95 (v7.0)
Released in 1995 with Microsoft Office for Windows 95, this is the first major version after Excel 5.0, as there is no Excel 6.0.

Internal rewrite to 32-bits. Almost no external changes, but faster and more stable.

Excel 97 (v8.0)
Included in Office 97 (for x86 and Alpha). This was a major upgrade that introduced the paper clip office assistant and featured standard VBA used instead of internal Excel Basic. It introduced the now-removed Natural Language labels.

This version of Excel includes a flight simulator as an Easter Egg.

Excel 2000 (v9.0)
Included in Office 2000. This was a minor upgrade, but introduced the upgrade to the clipboard where it can hold multiple objects at once. The Office Assistant, whose frequent unsolicited appearance in Excel 97 had annoyed many users, became less intrusive.

Excel 2002 (v10.0)
Included in Office XP. Very minor enhancements.

Excel 2003 (v11.0)
Included in Office 2003. Minor enhancements, most significant being the new Tables.

Excel 2007 (v12.0)
Included in Office 2007. This release was a major upgrade from the previous version. Similar to other updated Office products, Excel in 2007 used the new Ribbon menu system. This was different from what users were used to, but the number of mouse-clicks needed to reach a given functionality were generally fewer (e.g., removing gridlines only required two mouse-clicks instead of five). However, most business users agreed that the replacement of the straightforward menu system with the more convoluted ribbon dramatically reduced productivity.

Added functionality included the SmartArt set of editable business diagrams. Also added was an improved management of named variables through the Name Manager, and much improved flexibility in formatting graphs, which allow (x, y) coordinate labeling and lines of arbitrary weight. Several improvements to pivot tables were introduced.

Also like other office products, the Office Open XML file formats were introduced, including .xlsm for a workbook with macros and .xlsx for a workbook without macros.

Specifically, many of the size limitations of previous versions were greatly increased. To illustrate, the number of rows was now 1,048,576 (220) and columns was 16,384 (214; the far-right column is XFD). This changes what is a valid A1 reference versus a named range. This version made more extensive use of multiple cores for the calculation of spreadsheets; however, VBA macros are not handled in parallel and XLL add‑ins were only executed in parallel if they were thread-safe and this was indicated at registration.

Excel 2010 (v14.0)
Included in Office 2010, this is the next major version after v12.0, as version number 13 was skipped.

Minor enhancements and 64-bit support, including the following:
 * Multi-threading recalculation (MTR) for commonly used functions
 * Improved pivot tables
 * More conditional formatting options
 * Additional image editing capabilities
 * In-cell charts called sparklines
 * Ability to preview before pasting
 * Office 2010 backstage feature for document-related tasks
 * Ability to customize the Ribbon
 * Many new formulas, most highly specialized to improve accuracy

Excel 2013 (v15.0)
Included in Office 2013, along with a lot of new tools included in this release:
 * Improved Multi-threading and Memory Contention
 * FlashFill
 * Power View
 * PowerPivot
 * Timeline Slicer
 * Windows App
 * Inquire
 * 50 new functions

Apple Macintosh

 * 1985 Excel 1.0
 * 1988 Excel 1.5
 * 1989 Excel 2.2
 * 1990 Excel 3.0
 * 1992 Excel 4.0
 * 1993 Excel 5.0 (part of Office 4.X—Motorola 68000 version and first PowerPC version)
 * 1998 Excel 8.0 (part of Office 98)
 * 2000 Excel 9.0 (part of Office 2001)
 * 2001 Excel 10.0 (part of Office v. X)
 * 2004 Excel 11.0 (part of Office 2004)
 * 2008 Excel 12.0 (part of Office 2008)
 * 2011 Excel 14.0 (part of Office 2011)

OS/2

 * 1989 Excel 2.2
 * 1990 Excel 2.3
 * 1991 Excel 3.0

Trademark Dispute
Early in 1993 Excel became the target of a trademark lawsuit by another company already selling a software package named "Excel" in the finance industry. As the result of the dispute Microsoft had to refer to the program as "Microsoft Excel" in all of its formal press releases and legal documents. However, over time this practice has been ignored, and Microsoft cleared up the issue permanently when they purchased the trademark of the other program. Microsoft also encouraged the use of the letters XL as shorthand for the program; while this is no longer common, the program's icon on Windows (before Excel 2013) still consists of a stylized combination of the two letters, and the file extension of the default Excel format is .xls (.xlsx in newer versions).

Impact
Excel offers many user interface tweaks over the earliest electronic spreadsheets; however, the essence remains the same as in the original spreadsheet software, VisiCalc: the program displays cells organized in rows and columns, and each cell may contain data or a formula, with relative or absolute references to other cells.

Excel 2.0 for Windows, which was modeled after its Mac GUI-based counterpart, indirectly expanded the installed base of the then-nascent Windows environment. Excel 2.0 was released a month before Windows 2.0, and the installed base of Windows was so low at that point in 1987 that Microsoft had to bundle a run-time version of Windows 1.0 with Excel 2.0. Unlike Microsoft Word, there never was a DOS version of Excel.

Excel became the first spreadsheet to allow the user to define the appearance of spreadsheets (fonts, character attributes and cell appearance). It also introduced intelligent cell recomputation, where only cells dependent on the cell being modified are updated (previous spreadsheet programs recomputed everything all the time or waited for a specific user command). Excel introduced auto-fill, the ability to drag and expand the selection box to automatically copy cell or row contents to adjacent cells or rows, adjusting the copies intelligently by automatically incrementing cell references or contents. Excel also introduced extensive graphing capabilities.