What this 74F AND gate does on the board
The SN74F21N is a dual 4-input AND gate from Texas Instruments' 74F series, packaged in a 14-pin DIP (14-PDIP) for through-hole mounting. It performs the logical AND of four inputs per gate, with two independent gates in one package.
Supply voltage and logic thresholds
Runs on a 4.5V to 5.5V supply, which is the standard 5V TTL rail. The low-level input threshold is 0.8V max, and the high-level threshold is 2V min — so it's compatible with 5V TTL and most 5V CMOS families that meet those levels.
Speed and output drive — what 5.1ns and 20mA mean
Max propagation delay is 5.1ns at 5V with a 50pF load — that's fast enough for most 5V logic paths running at 50-100 MHz clock rates. The output can source 1mA and sink 20mA, so it drives typical TTL loads without extra buffering. Quiescent current draw is 4.3 mA max — negligible in a mixed-signal board, but worth noting if the 5V rail is shared with sensitive analog sections.
Package and board fit
14-DIP (0.300" body width, 7.62mm) with 0.100-inch pin pitch — a standard through-hole footprint that fits in sockets or solders directly. The 14-PDIP supplier package is the same mechanical outline.