Original Doctor V64 units sold by Bung did not allow the playing of backups. A person would have to modify the unit by themselves in order to make it backup friendly. This usually required a user to download and install a modified Doctor V64 BIOS. Additionally the cartridge adapter had to be opened and soldered in order to allow the operational procedure described early on this article. Though Bung never sold backup enabled V64s many re-sellers would modify the units themselves.