The purpose of this tiny little program is to reset drum counter of Laserjet III – compatibles laser printers (like the Olivetti PG308, that I owned).
Those printers have a little cartridge on which the drum counter is written. When the counter reach 10000, the printer stop working until a new drum unit (and a new cartridge) is loaded.
This is obviously a Bad Thing, and the fact that my drum unit printed more than 72000 sheets before I scraped the printer clearly prove this! :)
Just connect the cartridge to the PC parallel port with a special cable (also built by me), click on the Program button and counter is reset to 0 copies.
Clearly on my new printer (samsung CLX-3175… the worst printer I ever had!) there was a much sophisticated system to prevent use of compatible or refilled cartridges. But nothing that a big hole in the printer side and a switch soldered on the EEPROM write enable could not solve :)