On Atari 8-bit computers, the most common protection method was via "bad sectors". These were sectors on the disk that were intentionally unreadable by the disk drive. The software would look for these sectors when the program was loading and would stop loading if an error code was not returned when accessing these sectors. Special copy programs were available that would copy the disk and remember any bad sectors. The user could then use an application to spin the drive by constantly reading a single sector and display the drive RPM. With the disk drive top removed a small screwdriver could be used to slow the drive RPM below a certain point. Once the drive was slowed down the application could then go and write "bad sectors" where needed. When done the drive RPM was sped up back to normal and an uncracked copy was made. Of course cracking the software to expect good sectors made for readily copied disks without the need to meddle with the disk drive. As time went on more sophisticated methods were developed, but almost all involved some form of malformed disk data, such as a sector that might return different data on separate accesses due to bad data alignment. Products became available (from companies such as Happy Computers) which replaced the controller BIOS in Atari's "smart" drives. These upgraded drives allowed the user to make exact copies of the original program with copy protections in place on the new disk.