What's a normal copy speed between two internal hard disks?

What's a normal copy speed between two internal hard disks?

I have a PC with two internal SATA 7,200 RPM harddisks: one is a 1 TB Western Digital, and the other is 750 GB. I'm copying data between them, but it seems to be very slow: for example, to copy 140 GB takes about 5 hours.