To clarify: did any of the mask ROM or discrete IC vendors make and sell ROMS (or effective ROMs optimized by giant Karnaugh map) with fixed non-proprietary contents that could be used in building a circuit from stock, in addition to the normal custom ROMs.

A primary application would have been pre computed look-up-tables of really any common single-variable function.

For example:

  • A 64x8 ROM holding a quarter of a sine wave, or a "256x8" holding the full circle.
  • A ROM converting integer n to ln(n) and a companion converting fixed-point m to e^m.

There seem to be some 74-series chips that could be interpreted this way according to the listing on Wikipedia.

  • 74408 - 8-bit parity tree
  • 74630-35 - Error detection and correction chips

But these seem to be the exception rather than the rule and are likely to be much more efficient in practice.

If catalog stock ROMs were never sold why weren't they? What made them a bad fit for applications that could use them but couldn't justify custom silicon?

  • 2
    \$\begingroup\$ 7 segment decoders might qualify, especially if you include "effective ROMs optimized by giant Karnaugh map" as well as memory-like lookup tables. \$\endgroup\$ Commented Jan 8, 2018 at 7:11
  • \$\begingroup\$ If you search on e.g. digikey for some uncommon stateless 74 series ICs, then you will find a few which are marked "masked ROM" \$\endgroup\$
    – PlasmaHH
    Commented Jan 8, 2018 at 8:13

3 Answers 3


Character generator ROMs with 5x7 ASCII codes were certainly sold.

One example was the Signetics 2513, a rather nasty and sluggish P-MOS chip requiring three supply rails.

OTP and UV-erasable EPROMs came along not so long after- so the cost advantages of mask ROMs were not as significant as compared to mask charges (mask ROMs are not really fully custom silicon, only a metal layer was customized). Typical costs were low thousands of dollars and a MOQ in the thousands from US suppliers.

There were also small TTL OTP ROMs made with fuse technology.

And there were (and are) 4 and 8-bit micros pre-programmed for specific tasks, perhaps with an application-specific peripheral or two.

  • 6
    \$\begingroup\$ Signetics? The same who designed the famous write-only memory? Funny. Well, honestly, the requirement of +5/-5/-12 supply rails for a simple ROM almost look like a joke too (and it's even advertised as a "feature" in the datasheet). \$\endgroup\$
    – dim
    Commented Jan 8, 2018 at 12:43
  • \$\begingroup\$ @dim One assumes that data-sheet was printed very early in the April of 1972... I remember a UK electronics magazine – possibly Electronics Today International (ETI) – running a similar spoof data-sheet (pretty certain not a reprint of that one) one April in probably the latter half of the 70s. \$\endgroup\$
    – TripeHound
    Commented Jan 8, 2018 at 13:43

Certainly. I worked as a FAE for National, who produced a range of pre-programmed ROMs. Two I remember were a sine table lookup and a 7-segment to BCD converter. It's so long ago I can't remember part numbers or details.


There's also the 74F401 CRC generator which contains a ROM holding coefficients of different standard CRC polynominals, plus a shift register performing the calculations.


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