Which file(s) do I save when reformatting, to avoid a long download?

I need to reformat my harddrive and when I do I will need to reinstall COH.
For me, it can take hours to download, so is there a way to avoid this?
I have an external HD, which COH files can I save to avoid a long download? if this is possible.
thanks

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Global: @Fire Beam

To answer your question, the bulk of the download is the \City of Heroes\piggs\ directory, but to make it easier, you might as well just move the whole \City of Heroes\ folder over so you keep your default keybind files, saved costumes, and MA arcs as well.

If you are good with the registry, you can even save the CoH registry and reinstall it after as well so you don't lose your graphics preferences. If not, then don't even mess around with it.

Also, try this for more info:
Bill Z Bubba's Guide for Moving CoH or Installing Test

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great ty, and ty for the link

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Global: @Fire Beam