Classical computing is the conventional model used by most computers today. It processes information as bits, where each bit has a definite value of 0 or 1. CPUs, servers, laptops, phones, and most cloud systems all rely on this model, using logic gates and software to perform predictable calculations.
In cyber security, classical computing matters because nearly every attack and defense today runs on it. Malware, credential theft, vulnerability exploitation, and brute-force attacks all depend on classical systems and their limits. Defenders use the same environment for patching, endpoint protection, encryption, logging, and incident response. The term is also important in quantum discussions: quantum computers are not a replacement for classical systems, but a different computing model that may change some security assumptions, especially around cryptography.