If you've ever deleted a group of files in Windows and then panicked because you might have deleted the wrong files, the Undo function can seem like the most valuable function that exists. However, if you then realize that you had selected the right files after all -- and that it took 30 minutes to select them -- the Redo feature seems pretty valuable, too. You can undo an operation in Windows by pressing "Ctrl-Z" or selecting "Undo" from the Quick Access Toolbar. You can undo an undo by pressing "Ctrl-Y"or "Ctrl-Shift-Z," or by selecting "Redo" from the QAT.
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Undo and Redo
Each application in Windows maintains a buffer of recent operations that you can undo, and therefore redo. The size of the buffer depends on the application. For example, Microsoft Word, Excel and PowerPoint enable you to undo the last 100 typing actions or design changes, while Microsoft Access limits you to 20. As you successively press "Ctrl-Z," each previous action is undone in the order it was executed. The redo function works the same way, redoing the last actions you undid.
Some actions can't be undone, such as saving a file. For these types of actions, you can't undo or redo any actions preceding it. If you can't undo or redo an action and you're working in an application, you can close the file you're editing without saving changes to undo all changes you've made since the last time you saved the file. Microsoft Office applications provide an option for you to recover unsaved documents, workbooks or presentations.