I know that for instance an ATMega328 is a 8 bit MCU with 32k of program space, the same can be said for most other MCUs and some other ICs with a direct relation between the name and internal specs. I might be asking an irrelevant question, but I want to know out of interest.

I know that there is the 7400 and 4000 series with there specific voltage or performance specifications, what I don't understand is how the suffix of each series came about, such as a Hex Inverter = 04, or take the 74HC595(8 bit shift register) does the number relate to the internal structure? I understand the 74HC238, 3-to-8 line decoder, its numbering makes sense as to its function.

A CMOS inverter uses two MOSFETs:

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or a NAND gate with suffix '00

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  • Were the numbers given to a chip in a consecutive order or in relation to there development or are they related to their internal design?

1 Answer 1


In most (all?) cases there is some company-internal policy that determine the manner in which both the stem (74, Atmega, PIC16F, CD40, ....) and the suffix (00, 04, etc) are derived. Often they make little or no sense without the internal structure of the company. Once a company-specific type has gained widespread use and other vendors make it too, it might get standardized by some committee, which ads compromises and more confusion to the numbering scheme. More often a certain device becomes a 'de facto' standard, and at least part of its type number/name is adopted by other manufacturers. They will often add a company-specific prefix or replace the orginal one. Such generic products are often called by just their number: 7400, 555, 7805, 741. AFAIK SN7400, NE555, LM7805, uA741 are designations of the original manufacturers.

In short, there are no fixed rules.

  • \$\begingroup\$ thank you, that makes sense that a company would adopt a popular way of referring to a chip and confusing people. \$\endgroup\$
    – RSM
    Nov 18, 2014 at 18:34
  • 1
    \$\begingroup\$ Sometimes there are also legal reasons for name differences. One company I worked at had to change a bunch of their part numbers due to a lawsuit... \$\endgroup\$
    – MarkU
    Nov 18, 2014 at 21:05

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