Integrated Circuits
Families and scale
Integration runs from SSI (a few gates) through MSI and LSI to VLSI (millions of devices). TTL uses bipolar transistors: fast, current-hungry, traditionally a 5 V supply. CMOS uses field-effect transistors: almost no static current, but sensitive to static discharge. ECL is very fast and very power-hungry. Logic levels differ between families, so check compatibility before connecting them.
Key parameters
Fan-out (how many inputs one output can drive), propagation delay (speed), power dissipation, noise margin, and input/output current. Adding gates adds capacitance and delay, so a long chain can become slower than the clock allows.
Practical handling
Find pin 1 by the notch or dot, and check orientation before inserting a DIP. Use anti-static precautions even for parts that seem robust. Linear ICs include operational amplifiers, voltage regulators and timers; digital ICs include gates, memory, PLDs, FPGAs and ASICs.
Traps
CMOS inputs must never float - they oscillate and overheat; a floating TTL input usually reads as logic 1 because of the internal pull-up. Do not assume every 74-series part is pin-compatible with every other, and do not feed a regulator from a bus above its maximum input voltage.
Worked example
Replacing a 74LS00 (TTL) with a 74HC00 (CMOS) in a low-power circuit may work, but input threshold levels, unused-input rules and output drive differ. Verify the datasheet rather than substituting by pin count alone.