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Very-large-scale integration (VLSI) is the process of creating integrated circuits by combining thousands of transistor-based circuits into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The first semiconductor chips held one transistor each. Subsequent advances added more and more transistors, and as a consequence more individual functions or systems were integrated over time. The microprocessor is a VLSI device. The first "generation" of computers relied on vacuum tubes. Then came discrete semiconductor devices, followed by integrated circuits. The first Small-Scale Integration (SSI) ICs had small numbers of devices on a single chip — diodes, transistors, resistors and capacitors (no inductors though), making it possible to fabricate one or more logic gates on a single device. The fourth generation consisted of Large-Scale Integration (LSI), i.e. systems with at least a thousand logic gates. The natural successor to LSI was VLSI (many tens of thousands of gates on a single chip). Current technology has moved far past this mark and today's microprocessors have many millions of gates and hundreds of millions of individual transistors. As of mid-2006, billion-transistor processors are just on the horizon, with the first being Intel's Montecito Itanium Server. This is expected to become more commonplace as semiconductor fabrication moves from the current generation of 90 nanometer (90 nm) processes to the next 65 nm and 45 nm generations. At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like Ultra-large-scale Integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting more-than-VLSI levels of integration are no longer in widespread use. Even VLSI is now somewhat quaint, given the common assumption that all microprocessors are VLSI or better.
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