7400 series was from Texas Instruments and was originally all TTL (i.e. bipolar transistors). 4000 series came from RCA later and was originally all CMOS. 400

7400 series was from Texas Instruments and was originally all TTL (i.e. bipolar transistors). 4000 series came from RCA later and was originally all CMOS. 4000 was popular with designers because it used much lower power, had wider voltage range, and had higher fanout. But in the early days it was also slow, so not many famous computers were built with 4000 series. Later CMOS technology got fast and a funny thing happened: TI and other companies started building CMOS equivalents of 7400 series chips (with the letters HC in the middle for "High speed CMOS") and everybody adopted that system because they were drop-in replacements for the TTL parts but used much less power.