Clean install Yosemite

Before you do a clean install, you need to know why it is slow. Doing a clean install won't necessarily help.

If you are backing up to Time Machine wirelessly, it will slow your computer down while you are backing up unless you have a very good wireless connection.

Why won't it help??? I normally do that with a pc and it works

One question I already deleted the HD

Now it is telling me it will take over 10 hours to download osx yosemite

I have a time machine backup

Do I have to wait this 10 hours or can I simply use the time machine backup to restore???

It should not take 10 hours unless you have a slow internet connection. I just downloaded it myself to update my wife's computer from Mavericks and the download took 20 minutes.

If you are on a wireless network, make sure your computer is directly beside the router, or better still connect it by ethernet.

Otherwise, just let it run overnight.

Ok but can I just use the time machine backup instead of downloading it???

Yes. You could do that too. That won't be quite the same as doing a clean install, assuming that your original install was an incremental upgrade from Mavericks, rather than an original install of Yosemite.

If your original OS on that computer was Yosemite, then by all means copy it back from your Time Machine backup. The only thing you will have achieved, though, is to clear any disk directory corruption by reformatting your drive and you could probably have accomplished that by running Repair Disk from Disk Utility.

ok well just to clarify something if i leave it overnight to download and i erase my hard disk and install OS X that way.....

can i use the time machine backup after to restore everything or should i individually put back in all my programs e.g.

download chrome, paste back in my documents, download evernote etc etc???

When you install the OS, it will ask you whether you want to copy things back from a back up and you should answer yes and select Time Machine. No need to redownload apps and re-install.

Ok but that will still be considered a clean install right??

Yes.

SuperDuper and Carbon Copy Cloner are the DiskImage Utilities most commonly recommended.