Editing MOS Technology (section)

===Mask fixing===
Previous CPU designs, like the 6800, were produced using a device known as a [[Contact lithography|contact aligner]]. This was essentially a complex [[photocopier]], which optically reproduced a CPU design, or "mask", on the surface of the silicon chip. The name "contact" referred to the fact that the mask was placed directly on the surface of the chip, which had the significant disadvantage that it sometimes pulled away materials from the chip, which were then copied to subsequent chips. This caused the mask to become useless after about a dozen copies, and resulted in the vast majority of chips having fatal flaws; for a complex chip like the 6800, only about 10% of the chips would work once the masking process was complete.<ref name=Mensch/>

In 1974 [[Perkin-Elmer]] publicly introduced the [[Micralign]] system, the first projection scanner. Instead of placing the mask on the surface of the chip, it held it far from the surface and used highly accurate optics to project the image. Masks now lasted for thousands of copies instead of tens, and the flaw rate of the chips inverted so that perhaps 70% of the chips produced would work. The result was a similar inversion in pricing. The 6800 sold in small lots for {{US$|long=no|295}}; with no other changes than using a [[Micralign]], the same design could sell for {{US$|long=no|42}}.<ref name=Mensch/>

The change to the Micralign revealed a further advantage. Previously the masks were mass-produced by photography companies like [[Kodak]], who would make tens of thousands of copies of a master mask, or "[[reticle]]", and ship the masks to the aligners by the truckload. This meant that if a flaw was found in the design, it would cost a significant amount of money to fix it, as all the older masks would have to be thrown out. In contrast, with Micralign there was only one mask per aligner, so there was no inherent cost in replacing the mask if need be, although the cost, and especially time, of producing these master masks was considerable.<ref name=Mensch/>

MOS developed the ability to "fix" its masks after they had been produced.<ref name=Mensch>{{Cite web|url=https://archive.computerhistory.org/resources/access/text/2015/06/102739969-05-01-acc.pdf |title=Oral History of William David "Bill" Mensch, Jr. |last=Mensch|first=Bill|date=10 November 2014 |website=Computer History Museum |page=18}}</ref> This meant that as flaws in the design were discovered, the masks could be removed from the aligners, fixed, and put back in. This allowed them to rapidly drive out flaws in the original masks.

The company's production lines typically reversed the numbers others were achieving; even the early runs of a new CPU design&mdash;what would become the 6502&mdash;were achieving a success rate of 70 percent or better. This meant that not only were its designs faster, but they also cost much less as well.