Which is the smallest small-form-factor computer that uses desktop parts?

Question by C1N2G8: Which is the smallest small-form-factor computer that uses desktop parts?
Any suggestions for a very small computer that uses desktop parts (not laptop parts)? I don’t mind if it has some laptop parts but I want a desktop hard drive, since desktop HDs are much faster.

Best answer:

Answer by Mr O.
Mini-ITX allows you to use full size components. Check out http://www.logicsupply.com for some toys. Also, Shuttle makes small form factor computers that also allow you to use a full CPU and not something integrated so you have a more powerful PC.

Know better? Leave your own answer in the comments!