What Became Obsolete?#
The most useful question to ask about any classic part is not “how does it work?” but “would I still design it in today, and if not, what replaced it?” This table is the honest answer. It is deliberately blunt: some parts are genuinely dead, some are quietly immortal, and the difference is worth knowing before reaching for either.
| Part | Description | Still useful? | Modern replacement |
|---|---|---|---|
| 7490 | Decade (÷10) ripple counter | Mostly no | MCU timer |
| 74161 | 4-bit synchronous binary counter | Sometimes | FPGA / MCU |
| 74138 | 3-to-8 line decoder / demultiplexer | Yes | Often still used |
| 74HC595 | 8-bit serial-in, parallel-out shift register | Absolutely | Still common |
| 74HC14 | Hex Schmitt-trigger inverter | Absolutely | Still common |
| 74HC245 | Octal bus transceiver (direction-controlled) | Absolutely | Still common |
| 4066 | Quad bilateral (analog) switch | Absolutely | Still common |
| 555 | Timer / oscillator IC (astable & monostable) | Surprisingly yes | MCU timer or dedicated timer IC |
| EPROM | UV-erasable programmable ROM | Mostly hobby / retro | Flash |
| PAL | Programmable Array Logic (fuse-programmed) | Mostly obsolete | CPLD |
| GAL | Generic Array Logic (reprogrammable PAL) | Mostly obsolete | CPLD |
The pattern is not “old is dead.” It is that counting and sequencing migrated into microcontrollers and programmable logic, while interfacing, buffering, level translation, and analog switching stayed discrete because they still solve a physical problem no processor can absorb.