I am donating my computer to a charity. They will re-install the operating system on it but I need to make sure all my personal data is deleted before I ship it out. Is it enough to format the driv...

Any data recovery software can retrieve your data after formatting.

Although the charity probably won't go looking for old data, you have no idea what other uses will do.

The charity might just turn around and sell it and there are people who buy computers just to see if they can get old data from them. You should definitely wipe the drive. Use a program designed to make data unrecoverable like Active@ KillDisk.