2006 MacBook hard drive specifications

If you go for an SSD, then only go for the OWC Mercury Electra 3G SSD since any other SATA III SSD may not be compatible. That 3G SSD is a SATA II based SSD which makes it the most compatible option available. If that is the actual first 2006 white Macbook model using the Intel Core Duo 32bit CPU, then I really would not spend any money on that laptop because is has some serious firmware issues....definitely only install macOS on it or you may end up with a brick (personal experience twice over).

https://eshop.macsales.com/shop/ssd/owc/macbook/2006-current

Otherwise any 2TB or smaller 2.5" Hard Drive should work.

It looks like all of the Mac notebooks released in 2006 had a 1.5 Gbps SATA-I interface.

SATA-I probably won't be too much of a bottleneck for a 2.5" mechanical hard drive, but if you are putting in a 2.5" SATA SSD, that SATA-I interface will be a bottleneck.

The original MacBook used a generic laptop SATA hard disk drive, no more than 9.5 mm thick. Its capacity is not important.