When I started to learn about digital logic, the 7400-series devices simplified designs and experiments. At the time, Texas Instruments manufactured the SN74181 arithmetic-logic unit (ALU) in a 24-pin DIP and the SN7489 static memory that could store 16 4-bit values.  With these and some glue logic parts, engineers could build basic computational circuits.  If you think that sounds far fetched, remember that minicomputers of the time ('60's and '70's) used small-scale logic ICs throughout, although they used core memory for storage.

As designers used more microprocessors in new circuits, the basic 7400-series devices and their offspring in similar TTL and CMOS families became used more as glue logic that connected larger processor, memory, I/O ports and timing ICs.  More sophisticated (at the time) microprocessors used companion I/O chips that supplied everything from basic digital ports to floppy-disk controllers, display controllers, and so on. The resulting circuits used fewer and fewer glue-logic chips.

When I look at a design today, microcontrollers (MCUs) and special-purpose I/O devices have eliminated the need for basic logic functions such as gates, flip flops, latches, counters, and shift registers. A current MCU development kit might include a TTL-to-RS232 interface chip, but only if the kit provides a serial-port connection.

Distributors still sell basic glue-logic ICs, but the list had shrunk and prices have gone up. These days if you need glue logic you move the necessary functions into MCU or FPGA code and assign them I/O pins. Or, you drop an MCU into a circuit and program it for what you need. You can get a low-power 8051 MCU in a 4x4mm package, so what's not to like?

Glue circuits still have a place in analog circuits, though. Amplifiers, filters, voltage regulators, and similar devices still provide functions that an MCU just can't. I suppose we'll have discrete analog "glue" for some time.

I still have several dozen parts drawers full of 7400-series-type devices. Will they ever get used? Time will tell.  I also have a few arrays of core memory but no plans for them in new projects.

--Jon Titus