Computer Hardware Unit Computer Engineering

Computer memory

Any medium that allows a computer to store and/or retrieve data (e.g., magnetic hard drives or flash memory made of transistors).

Volatile memory

Memory that does NOT retain its contents after the computer is turned off. Examples: SRAM (cache/registers), SDRAM-DDR (system memory). Generally faster.

Non-volatile memory

Memory that DOES retain its contents after the computer is turned off. Examples: Spindle HDD, SSD, NVMe, Flash, EEPROM. Generally slower.

BIOS / UEFI

Non-volatile chip that performs POST, reads/stores CMOS parameters, and loads/hands control to the operating system.

POST (Power On Self Test)

A diagnostic test run by the BIOS each time the computer boots to verify hardware is functioning correctly.

CMOS

Memory that stores system parameters such as hard drive count, boot order, security passwords, and the system clock.

Operating System (OS)

Software that provides a user interface, manages hardware via drivers, and manages software applications. Examples: Windows, Linux, macOS.

SRAM

Static RAM — a type of volatile memory used for CPU cache and registers. Faster but more expensive than SDRAM.

SDRAM-DDR

Synchronous Dynamic RAM (Double Data Rate) — the main system memory in a computer. Volatile and generally faster than storage but slower than cache.

FSB (Front Side Bus)

A legacy bus from the 1990s–2000s that carried data from the CPU to the Northbridge memory controller hub.

Northbridge

A legacy chipset component (memory controller hub) that managed high-speed communication between the CPU, RAM, and graphics. Now integrated into the CPU die.

Southbridge

A legacy chipset component (I/O controller hub) that managed slower peripherals: IDE, SATA, USB, audio, Ethernet. Its functions are now part of the modern chipset.

PCI (Peripheral Component Interconnect)

A legacy expansion bus for connecting peripheral devices. Phased out by PCIe (PCI Express) in 2004.

AGP (Accelerated Graphics Port)

A legacy high-speed port for connecting video cards to the motherboard. Phased out by PCIe in 2004.

PCIe (PCI Express)

The current standard expansion bus. PCIe 3.0 is almost always connected directly to the CPU; PCIe 2.0 may connect to either the CPU or chipset.

Modern chipset

Replaces both Northbridge and Southbridge. Recent Intel/AMD CPUs integrate Northbridge functions into the CPU die, leaving the chipset to handle Southbridge and SuperI/O functions.

SuperI/O chip

A chip that historically managed legacy low-speed I/O: serial port, parallel port, floppy disk, keyboard, mouse. Its functions are now absorbed into the chipset.

SATA connector

Internal connector used to connect hard drives, optical drives, and other peripherals to a modern motherboard.

ATX power supply connector

Internal connector providing power from the PSU to the motherboard. Typically a 24-pin main connector plus a 4/8-pin CPU power connector.

DIMM slot

Slot on the motherboard that holds SDRAM DDR4 (or DDR5) system memory modules.

M.2 slot

A compact internal slot on modern motherboards used to install NVMe SSD modules.

USB Type E header

Internal motherboard header for USB 3.0 Type-C connections on the front panel of the computer case.

USB 20-pin header

Internal header on a modern motherboard used to connect two front-panel USB 3.0 Type-A ports.

USB 10-pin header

Internal header on a modern motherboard used to connect front-panel USB 2.0 Type-A ports.

Front panel header

Internal connector linking the motherboard to the case's front panel: power switch, reset switch, HDD LED, and power LED.

IDE connector (legacy)

Legacy internal connector using wide ribbon cables to connect hard drives and optical drives. Replaced by SATA.

ISA slot (legacy)

A very old expansion slot used before PCI for connecting legacy expansion cards.

AGP slot (legacy)

Legacy high-speed slot for graphics cards. Replaced by PCIe.

CPU (Central Processing Unit)

The brain of the computer. It executes program instructions, performs arithmetic/logic, manages memory, controls I/O devices, and coordinates all hardware.

Fetch-Decode-Execute cycle

The fundamental CPU operation: (1) Fetch instruction from RAM, (2) Decode it into CPU signals, (3) Execute the operation. Repeated billions of times per second.

ALU (Arithmetic Logic Unit)

CPU component that performs all arithmetic (+, −, ×, ÷) and logic operations (AND, OR, NOT). The actual computing engine.

Control Unit (CU)

CPU component that fetches instructions, decodes them, and directs signals to all other CPU components.

Registers

Tiny, ultra-fast storage inside the CPU that holds data currently being processed. The fastest memory in the hierarchy.

Cache (L1 / L2 / L3)

On-chip memory 10–100× faster than RAM. L1 is fastest/smallest (~32–64 KB); L3 is largest/slowest (~8–64 MB). Hit rates reach 90–99%.

Clock speed

The number of cycles per second a CPU completes, measured in GHz. Modern CPUs run at 3–6+ GHz. Plateaued around 2004 due to the "heat wall".

Moore's Law

Proposed by Gordon Moore (Intel co-founder) in 1965: the number of transistors on a chip doubles approximately every 2 years while costs remain the same.

Transistor

A tiny electronic switch (ON = 1, OFF = 0) that forms the building block of all computation. Modern CPUs use billions of them at sizes of 3–5 nm.

Multi-core CPU

A CPU with multiple independent processing cores on one die, enabling true parallel processing. Industry standard since 2005.

Physical core

An actual, independent processing unit etched on the silicon die, with its own ALU, CU, L1/L2 cache, registers, and execution pipelines.

Logical Core ( Thread )

A software-defined view of a core seen by the OS, created by Hyperthreading/SMT or virtualization. Shares the physical core's hardware resources.

Hyperthreading / SMT

Technology that lets one physical core run two threads simultaneously by duplicating registers and sharing the ALU/cache. Gives a 10–30% throughput boost. 1 physical core → 2 logical cores.

Memory hierarchy (fastest → slowest)

Registers → L1 Cache → L2 Cache → L3 Cache → RAM. Faster memory is smaller and more expensive. Cache hit rates reach 90–99%.

Cache miss

When data the CPU needs is not found in cache and must be fetched from RAM (200+ cycles, ~60 ns) instead of cache (~4 cycles, <1 ns).

Program Counter

A CPU register that keeps track of which instruction to fetch next during the Fetch-Decode-Execute cycle.

What is a Bus in computer architecture, and what are its three primary components?

A Bus is a communication "highway" (a set of physical wire traces) that transfers data between internal components like the CPU, RAM, and peripherals.