family; it became the most popular variant once it was widely available. Many 74LS ICs can be found in microcomputers and digital consumer electronics manufactured in the 1980s and early 1990s. The 74F family was introduced by Fairchild Semiconductor and adopted by other manufacturers; it is faster than the 74, 74LS and 74S families. Through the late 1980s and 1990s newer versions of this family were introduced to support the lower operating voltages used in newer CPU devices. Part numbering Part number schemes varied by manufacturer. The part numbers for 7400-series logic devices often use the following designators: Often first, a two or three letter prefix, denoting the manufacturer and flow class of the device. These codes are no longer closely associated with a single manufacturer, for example, Fairchild Semiconductor manufactures parts with MM and DM prefixes, and no prefixes. Examples: SN: Texas Instruments using a commercial processing SNV: Texas Instruments using military processing M: ST Microelectronics DM: National Semiconductor UT: Cobham PLC SG: Sylvania Two digits for temperature range. Examples: 54: military temperature range 64: short-lived historical series with intermediate "industrial" temperature range 74: commercial temperature range device Zero to four letters denoting the logic subfamily. Examples: zero letters: basic bipolar TTL LS: low speed Schottky HCT: High-speed CMOS compatible with TTL Two or more arbitrarily assigned digits that identify the function of the device. There are hundreds of different devices in each family. Additional suffix letters and numbers may be appended to denote the package type, quality grade, or other information, but this varies widely by manufacturer. For example, "SN5400N" signifies that the part is a 7400-series IC probably manufactured by Texas Instruments ("SN" originally meaning "Semiconductor Network") using commercial processing, is of the military temperature rating ("54"), and is of the TTL family (absence of a family designator), its function being the quad 2-input NAND gate ("00") implemented in a plastic through-hole DIP package ("N"). Many logic families maintain a consistent use of the device numbers as an aid to designers. Often a part from a different 74x00 subfamily could be substituted ("drop-in replacement") in a circuit, with the same function and pin-out yet more appropriate characteristics for an application (perhaps speed or power consumption), which was a large part of the appeal of the 74C00 series over the competing CD4000B series, for example. But there are a few exceptions where incompatibilities (mainly in pin-out) across the