IC memory

Chapter IC memory

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • Electronic wristwatches, single-chip calculators, and small microcomputers are ex-amples of devices using LSI ICs. They can be 10 times more sophisticated than MSI de-vices.VLSIVery-large-scale integration (VLSI) devices have from 1,000 to 10,000 componentsper chip. This is an order of magnitude more dense than LSI. Complex microcomputers,and peripheral circuits such as memory storage ICs, are made using VLSI.ULSI, ELSI, and OLSIYou might sometimes hear of ultra-large-scale integration (ULSI). Devices of thiskind have more than 10,000 elements per chip. The principal use for this technology liesin ever-larger random-access memory (RAM) capability for personal computing.In the future, you can expect new names to arise to fit new technologies. But com-mon sense will ultimately prevail over the ridiculous. While abbreviations like “ELSI,”for “extremely large-scale integration,” might be coined (this one happens to be anacronym, too), engineers have to be careful. What is “extremely dense” at one point intime might be “ho-hum” a few years later. No one wants to be cornered into christeninga new invention with some laughable name like “OLSI” (overwhelmingly large-scale in-tegration), just because all the other superlatives have been used up.IC memoryBinary digital data, in the form of high and low levels (logic ones and zeros), can bestored in ICs. Data storage is generally known as memory. In ICs, memory can take var-ious forms.RAMA random-access memory (RAM) stores binary data in arrays. The data can be ad-dressed (selected) from anywhere in the matrix. Data is easily changed and stored backin RAM, in whole or in any part. A RAM is sometimes called a read/write memory.An example of RAM is a word-processing computer file that you are actively work-ing on. This paragraph, this chapter, and in fact the whole text of this book was writtenin semiconductor RAM before being stored on disk (another kind of RAM) and ulti-mately printed on the paper now before you.There are two kinds of RAM: dynamic RAM (DRAM) and static RAM (SRAM). ADRAM employs IC transistors and capacitors, and data is stored as charges on the ca-pacitors. The charge must be replenished frequently, or it will be lost via discharge. Re-plenishing is done automatically several hundred times per second. An SRAM uses acircuit called a flip-flop to store the data. This gets rid of the need for constant replen-ishing of charge, but the tradeoff is that SRAM ICs require more elements to store agiven amount of data.With any RAM, the data is erased when the appliance is switched off, unless someprovision is made for memory backup. The most common means of memory backup isthe use of a cell or battery. Modern IC memories need so little current to store their datathat a backup battery lasts as long in the circuit as it would on the shelf.530 Integrated circuits and data storage media