How Do Computers Really Work? Inside CPU, Memory, and Compilers Explained

Computer Architecture Basics

A computer is a machine that manipulates data according to instructions, consisting mainly of a processor (CPU) and memory (RAM). Memory stores both instructions and data, while the CPU fetches instructions from memory, performs calculations, and writes results back.

Memory

Memory is divided into many cells, each identified by a numeric address. Accessing a cell involves reading or writing a small amount of data, typically a byte (8 bits). Addresses are transmitted as binary numbers over signal lines.

Binary numbers use base‑2 representation.

Signal lines carry bits: high voltage for "1" and low voltage for "0". Buses transfer groups of signals; an 8‑line address bus can address 2⁸ bytes, while an 8‑line data bus transfers bytes to and from memory.

CPU

The CPU contains registers—small internal storage units that perform simple arithmetic and move data between registers and RAM. Typical operations include copying data between memory locations and registers, and adding register values.

The set of all possible CPU operations is called the instruction set; each operation is encoded as a numeric opcode stored in RAM. Programs are sequences of these opcodes.

Self‑modifying code can be used by viruses to evade detection, similar to how biological viruses alter DNA.

CPU execution follows a fetch‑decode‑execute cycle controlled by the program counter (PC): fetch instruction at PC, increment PC, execute instruction, repeat.

Conditional branching allows the CPU to jump to different instruction addresses, enabling complex control flow.

CPU Architectures

Different CPUs use different instruction sets (e.g., x86 for most PCs, ARM for smartphones). This explains why software compiled for one architecture cannot run on another without translation.

Early CPUs were 4‑bit (Intel 4004), later 8‑bit, 16‑bit, 32‑bit, and today 64‑bit, each increasing addressable memory and register width.

Endianness

Byte order determines how multi‑byte numbers are stored: little‑endian stores the least‑significant byte first, big‑endian stores the most‑significant byte first. Most modern CPUs use little‑endian, but network protocols often use big‑endian.

Compilers

Compilers translate high‑level programming languages into CPU instructions. They perform optimizations such as eliminating redundant calculations and converting recursive functions into iterative forms.

if x = 0
compute_this()
else
compute_that()

Optimizing compilers can rewrite code to reduce instruction count and improve performance.

Scripting Languages

Scripting languages (e.g., JavaScript, Python, Ruby) are interpreted at runtime, offering faster development cycles at the cost of execution speed compared to compiled code.

Operating Systems

Compiled programs rely on the operating system for I/O operations. System calls abstract hardware differences, allowing the same program to run on different machines only if the OS and CPU architecture match.

Disassembly and Reverse Engineering

Binary programs can be disassembled to reveal the underlying CPU instructions, a technique used in reverse engineering and security research.

Open‑Source Software

Open‑source code can be inspected and modified, improving security transparency compared to closed‑source systems.

Memory Hierarchy

To bridge the speed gap between the fast CPU and slower RAM, modern CPUs include multiple cache levels (L1, L2, L3). Caches store frequently accessed data, exploiting temporal and spatial locality to reduce costly RAM accesses.

Typical access times: CPU register < 1 ns, L1 cache ≈10 ns, L2 ≈100 ns, RAM ≈100 ns‑1 µs, SSD ≈0.1 ms, HDD ≈1 ms, network storage >10 ms.

Effective use of caches dramatically improves overall system performance.

Storage Technologies

Beyond RAM, secondary storage (hard disks, SSDs) provides larger capacity but higher latency. Modern systems use SSDs or hybrid drives to balance speed and cost.