A computer system consists of hardware (physical components) and software (programs). Understanding how the CPU processes data, how memory stores information, and how software manages everything is foundational to computer science.
CPU (Central Processing Unit): the brain. Three parts — ALU (arithmetic/logic operations), CU (control unit — fetches and executes instructions), Registers (tiny, ultra-fast storage inside CPU). Memory hierarchy (fastest to largest): Registers → Cache (L1, L2, L3) → RAM (volatile, working memory) → Secondary Storage (HDD, SSD — permanent). RAM: fast but lost on power off. ROM: permanent, stores boot instructions (BIOS/UEFI). Speed vs capacity trade-off: CPU cache is fastest but smallest; HDD is largest but slowest.
System software: manages hardware, provides platform. OS (Windows, Linux, macOS) — memory management, process scheduling, file system, device drivers. Utility software: antivirus, disk defragmenter, backup tools. Application software: user-facing programs — MS Office, browsers, games, Photoshop. Firmware: software embedded in hardware (printer firmware, BIOS). Booting: process of loading OS from storage into RAM when computer starts (POST → BIOS → Boot Loader → OS Kernel).
RAM (Random Access Memory): volatile (data lost on power off), read-write, used for running programs and active data, relatively fast. Available in GBs (8GB, 16GB). ROM (Read Only Memory): non-volatile (data persists without power), read-only (or rarely written), stores firmware and boot instructions. Much smaller capacity. RAM is like a desk (working space) — cleared when you leave. ROM is like a permanently printed instruction manual.
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