Learn in the textbookIP Addresses and the Address System
DefinitionIPv4 is version 4 of IP, the internet's communication protocol, and it writes an address in 32 bits (32ビット).
ExplanationIt can express 2 to the 32nd power addresses, roughly 4.3 billion, and the shortage became a problem as more devices came online. To write one, you split the 32 bits into four groups of 8 bits, turn each group into a decimal number from 0 to 255, and join them with dots.
AnalogyThink of a membership number with a fixed length. Unless you add digits, the total supply of numbers stays the same however many members join.
Memory hookThe 4 in v4 is a version number, but it happens to match the number of dotted groups, so you can recall 4 groups × 8 bits = 32.