“OPC” means Organic Photoconductor, a fundamental part of any laser Cartridge or copying device. Depending on its shape it is categorized as a drum or a belt. The word “organic” in Organic Photoconductor (OPC) indicates that the photoreceptor's coating is manufactured from organic (carbon-based) chemical compounds. These photoconductive compounds are actually petrochemical derivatives originating from the fossil fuels petroleum, natural gas, and coal.
By and large, OPC drums are considered the most "environmentally friendly" photoreceptors available today predominantly because their designers and manufacturers deliberately utilize non-hazardous raw materials against hazardous alternatives of photoreceptors such as arsenic triselenide (As2Se3) and selenium tellurium (SeTe) drums.

A German firm was the first to officially introduce OPC formula, in 1950`s.Later IBM in 1970`s made further progression and Canon in 1980`s came with the OPC cartridge-based “personal copier” (PC) and subsequent laser printer (LP) engines. This revolutionized the OPC production worldwide

OPC Drum plays a vital role in the process of non-impact printing. At the center of the imaging process is the organic photoconductive or OPC drum. The drum is a photo diode; it accepts and holds the charge. When it is exposed to light the organic layers become conductive and active, thus allowing the charge to migrate to zero potential. In this stage, a laser beam passes through an opening in the cartridge and focuses to discharge the charge on the drum surface. This creates a latent image on the drum. This image area will attract toner in the developing process.
Developing process contains many major components, including toner, developer roller assembly, metering blade and the AC/DC bias. Toner is attracted to the developer roller either by an internal magnet or by an electro static charge. The roller carries the toner particles to the metering blade (doctor blade), where toner tumbles creating a tribo-electric charge (friction) on the surface of the toner particles. The metering blade (doctor blade) then allows an evenly distributed amount of toner to pass to the OPC drum. Once the toner particle has passed beyond the doctor blade, then developer roller is charged with an AC/DC bias from the High Voltage Power Supply. This charge allows the toner particles to “jump” from the developer roller to the OPC drum attracting the latent image. At this point, the hidden image on the drum is transferred onto a sheet of paper.

Of course, the Drum of your toner cartridge won't last forever. It's not life time guaranteed. The average drum life is no more than two refilling cycles. However, it could last more or less than that.
The drum life will depend on how long you use your equipment uninterrupted and/or the thickness of the paper that you are using for you printing jobs. Any paper more than 20 lbs thicker will wear out your drum faster.
As the drum is the "soul" of the cartridge, it should be in good condition for you to have good print results.