Inside Intel. Tim Jackson

could ‘write’ the data into this new kind of ROM in a few minutes – and the prototyping cycle for a new computer product would be cut from months to hours.

      Moore did not need to see Frohman’s demonstration twice before committing the company to turning it into a commercial product. Soon after the development programme began, however, Frohman came back with some even better news. It wasn’t just writing data to his new kind of ROM that was easy. The chip could be easily erased too, using ultraviolet light. So if the circuit designers found that they had made a mistake, or decided to make some improvements to their design, all they needed to do was to take the ROM chip off the circuit board it was installed on, open up its top, and shine a UV beam on it. The chip would then be like new, ready to receive a fresh set of data. Intel decided to call it an erasable, programmable read-only memory (EPROM).

      Before the EPROM was ready for sale, the company had to find a way of manufacturing it at reasonable cost. The design’s first manifestation, a chip with a capacity of 2 kilobytes (2K) was from this point of view a disaster – it was half as big again as the biggest chip Intel had ever made. Simple arithmetic meant that you’d get fewer devices, or ‘dice’, off each silicon wafer if the chips were bigger, so the average cost of each one would be higher. But there was a further penalty for trying to build bigger devices. One of the key sources of failure came from random flaws in the silicon wafer itself. Other things being equal, a bigger die size would mean that a higher percentage of the devices that came off the fab line would be flawed. The outlandish size of the first EPROM also presented a more prosaic problem. The chip was so big that its design didn’t fit on the layout tables. The circuits had to be assembled from four smaller layouts stuck together – which created alignment problems.