From Microsoft's help file
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Automatically save a backup copy of a workbook

You can use AutoRecover to have Excel automatically save a backup copy each
time you save a workbook. The backup copy provides you with a previously
saved copy, so you have the current saved information in the original
workbook and the information saved prior to that in the backup copy. Each
time you save the workbook, a new backup copy replaces the existing backup
copy. Saving a backup copy can protect your work if you accidentally save
changes that you don't want to keep or delete the original file.

On the Tools menu, click Options.
On the Save tab, select the Save AutoRecover info every check box.
In the minutes box, type or select a number to specify the interval for how
often you want to save files.
The more frequently your files are saved, the more information is recovered
if there is a power failure or similar problem while a file is open.

Note: AutoRecover is not a replacement for regularly saving your files. If
you choose not to save the recovery file after opening it, the file is
deleted and your unsaved changes are lost. If you save the recovery file, it
replaces the original file (unless you specify a new file name).

"Rykar2" wrote:

Hi there,
What I'm trying to do is work in a spreadsheet and having an exact one as a
backup, like when you link cells and when you change one cell the other one
change too, but in this case I need the whole spreadsheet, when I work in one
the other one change, add or delete data too. It would work like a mirror
hard drive.
Is this posible?
Thanks in advance.
Rick