Topic 3: Hardware — Part 4

Data Storage

Primary storage

Primary storage is directly accessible by the CPU and provides workspace for running programs.

Feature	RAM (Random Access Memory)	ROM (Read-Only Memory)
Volatility	Volatile: contents lost when power is off.	Non-volatile: contents retained when power is off.
Read/Write	Can be read from and written to.	Read-only during normal operation.
Purpose	Holds OS, running apps, and current data.	Holds boot-up instructions (firmware).

Exam Traps

RAM holds the OS and running programs; ROM stores boot-up/firmware instructions — do not say ROM holds currently running applications.

Secondary storage is non-volatile storage not directly accessible by the CPU, required for permanent data retention.

Type	Technical Operation	Examples
Magnetic	Uses spinning platters divided into tracks and sectors; data read/written using electromagnets.	HDD (Hard Disk Drive).
Optical	Uses lasers to create and read pits and lands in a spiral track.	CD, DVD, Blu-ray.
Solid-State (Flash)	Uses NAND or NOR technology; transistors act as control gates and floating gates to trap electrons.	SSD, SD card, USB flash drive.

Purpose: Used when RAM is full to allow more programs to run than physical memory allows.
Process: The OS moves data not currently needed from RAM to a space on secondary storage (HDD/SSD). Pages of data are transferred between RAM and virtual memory when needed.
Limitation: Accessing data from virtual memory is significantly slower than using RAM alone.

Definition: Files are stored in a remote location on physical servers (magnetic or solid-state) accessed via a network connection.

Advantages	Disadvantages
Access data from any place or device.	Relies on high-bandwidth internet access.
Easy to share data publicly or with others.	Potential privacy and security issues.
Reduces need for expensive local secondary storage.	Ongoing costs could be higher long-term.

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