Why have I got so much system data on my Mac?

[rogercorke]

When you go to the Storage section in "About This Mac", you get a bar chart that supposedly shows how much of the storage is taken up by each type of data. I attach mine, which supposedly shows I've got 659.96GB of System Data. Can this possibly be right, especially as yesterday the same bar chart showed I had only 500GB of System Data!

Also, the yellow bar shows I have just 28GB of photos. In fact, I've got more than 300GB of photos.

 

[apostolosdt]

As far as I understand it, large System Data are typical with Macs; that's why it is a good idea to occasionally run sth like OnyX or, more drastically, restart the machine.

Right now, I have more than 76GB System Data, on a 500GB disk.