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What does X denotes in ASPX, DOCX, XLSX, PPTX etc?

It's one of those things you just take for granted until one day someone asks you and you realize you can't answer it. Much like for years I never questioned the use of 1033 directories in Microsoft products for years until one day, someone asked me about it.

Around the release of .NET and Office 2007, Microsoft added an x to basically all of their extensions and I frankly took it as representing XML, but that simply doesn't make sense with .aspx.

So, I realize this is a very non technical question, but now that the question has been asked of me and my googling hasn't given me an answer, can anyone tell me with authority what the X represents? Is it extended? Xml? Or is there no meaning behind it?

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migrated from Jun 14 '10 at 22:07

This question came from our site for professional and enthusiast programmers.

marked as duplicate by Ignacio Vazquez-Abrams, Nifle, Sathya, Joey, MDMarra Jun 15 '10 at 1:07

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Does it need to represent something? – drewk Jun 14 '10 at 22:00
Well, that is very possibly an answer and quite possibly the valid one. So, it could come back the 'X' literally means nothing... that is exactly what I am asking. Generally though, file extensions do represent something. – Serapth Jun 14 '10 at 22:04
Yes, you've got problems! :-) in the case of aspx it is because it contains xhtml or is an extension of asp. In the case of docx and xlsx it is the Office Open XML format or was it Open Office XML, that was a good MS trick to cause confusion... – jdehaan Jun 14 '10 at 22:04
"X-tra awesome". – ceejayoz Jun 14 '10 at 22:04
... sure, make me associate to SuperUser! ;) – Serapth Jun 14 '10 at 22:09

It is because of XML format used inside those files.

some explanation:

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IIRC the successor of (classic) ASP was first called ASP+, before it was released as ASP.NET. So maybe this is where the X in ASPX comes from (a + rotated by 45 degrees).

For the office documents, it's probably because the files are XML based.

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I guess it's named .aspx (maybe extended) to be able to differentiate ASP pages (.asp) from ASP.NET pages.

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microsoft converted there original .doc which is a document and .xls (I belive it stands or extendable ledger sheet) to docx which is document + xml (which stands for extendable markup language) and .xlsx which again is a xml based spread sheet

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