Computers from Transistors; The Solid-State Century; Scientific American Presents; by Staff Editor; 3 Page(s)

The average midrange personal computer generally contains between 50 and 75 integrated circuits, better known as chips. The most complex of these chips is the microprocessor, which executes a stream of instructions that operate on data. The microprocessor has direct access to an array of dynamic random-access memory (DRAM) chips, where instructions and data are temporarily stored for execution. A high-end, stateof--the-art PC might have eight DRAM chips, each capable of storing 8,388,608 bytes (64 megabits) of data. In addition to the microprocessor and DRAMs, there are many other kinds of chips, which perform such tasks as synchronization and communication.

The transistors in an integrated circuit are of a type known as complementary metal oxide semiconductor (CMOS). They have two regions, the source and the drain, that have an abundance of electrons and are therefore referred to as n (for "negative") type. In between the source and drain is a p-("positive") type region, with a surplus of electron deficiencies (called holes).