All of the PC CPU's are x86, x standing for 8086, 286, 486, the same as Win9x covers Windows 95, 98 and 98se. As Ottoman said, it is the underlying architecture of these CPU's. Once Intel started marketing their CPU's by name instead of numeric designation, everyone else followed suit. The micron size refers to the process used to cut the transistors into the silicon wafer that is the heart of the CPU. The smaller the micron size, the more transistors can be cut into it, resulting in many improvements, such as cooler running. With the Pentium 75 in 1994, Intel were using 0.6 micron process technology, which allows 21,000 lines per inch. We've come a long way!