AT&T licensed Version 5 to educational institutions, and Version 6 also to commercial sites. Schools paid $200 and others $20,000, discouraging most commercial use, but Version 6 was the most widely used version into the 1980s. Research Unix versions are often referred to by the edition of the manual that describes them, because early versions and the last few were never officially released outside of Bell Labs, and grew organically. So, the first Research Unix would be the First Edition, and the last the Tenth Edition. Another common way of referring to them is Version "x" (or V"x") Unix, where "x" is the manual edition. All modern editions of Unix—excepting Unix-like implementations such as Coherent, Minix, and Linux—derive from the 7th Edition.