Is it true that in OS 10 Time Machine automatically backs up to your internal hard drive?

Laptops store local Snapshots

See...

http://pondini.org/TM/30.html

If you want to disable them see..

http://osxdaily.com/2011/09/28/disable-time-machine-local-backups-in-mac-os-x-li on/

This is true for laptops that are not regularly connected to their normal Time Machine backup drive. It will also function on a desktop model whose backup drive is often disconnected.

In theory these "snapshots" are transferred from your computer to the backup drive when it is connected, then deleted from the computer. They should not affect your real available space on the drive. See OS X Lion- About Time Machine's "local snapshots" on portable Macs.

You can disable the feature:

Open the Terminal in the Utilities folder and enter or paste the appropriate command line. Press RETURN and enter your admin password when prompted. It will not be echoed.

To turn them ON: sudo tmutil enablelocal

To turn them OFF: sudo tmutil disablelocal

Note that turning them OFF will also delete all existing snapshots.

KLCambridge wrote:

. . .

Something seems out of control. There's no way I've needed an additional 24 GB of back ups since yesterday. Is this normal?

If you've changed, moved, or deleted a lot of stuff, that could be correct.

Can I turn off, or at least limit, the backing up that's taking place?

In most cases, there's no need. Local Snapshots are "expendable" -- they'll be deleted automatically as needed to keep your disk below 80% full. In any case, they're reduced to one per day after 24 hours, then deleted after a week.

See Time Machine - Frequently Asked Question #30 for the gory details.

Kappy wrote:

This is true for laptops that are not regularly connected to their normal Time Machine backup drive. It will also function on a desktop model whose backup drive is often disconnected.

They're made on laptops whenever Time Machine is ON, whether the backup drive (or network destination) is available or not. And they're not made on a desktop Mac unless turned-on specifically via the Terminal command.

In theory these "snapshots" are transferred from your computer to the backup drive when it is connected, then deleted from the computer.

They're never copied to the backup drive. That was true in some early beta versions of Lion (and still posted on some of the rumor sites), but was removed long ago.

Yes, I forgot to include that. I thought about it later, but too late to edit. Thanks for the correction.