Summary of Secondary Storage Devices and Media

## Introduction Storage devices allow for non-volatile data storage, meaning they retain data even when the computer is powered off. In secondary education, three main technologies are primarily used: magnetic, optical, and solid-state. In this material, we will focus on **magnetic media** and **flash memory / cards** (solid-state), excluding details about optical media and SSDs as instructed. > Definition: A **storage medium** is the physical material where data is recorded (for example, a disk), and a **storage device** is the hardware that reads from and writes to that medium (for example, a disk drive). ## 1. Magnetic Media and Devices ### 1.1 What is Magnetic Storage? Magnetic storage uses materials with magnetic properties (e.g., iron oxide) onto which patterns representing 1s and 0s are recorded. A read/write head detects or alters the magnetization of the medium. > Definition: **Magnetic storage** stores data by magnetically orienting particles on a surface or tape. ### 1.2 Main Magnetic Devices - **Magnetic Tape**: plastic reels or cassettes coated with magnetic oxide. Data is read/written sequentially. - **Hard Disk Drive (HDD)**: spinning platters with magnetic layers; read/write heads float above each surface to read and write. - **Portable Hard Drive**: an HDD in an external enclosure for backups and data transport. Comparative Table: Magnetic Media | Feature | Magnetic Tape | Hard Disk Drive (HDD) | Portable Hard Drive | |---|---:|---:|---:| | Data Access | Sequential (slow) | Random (faster) | Random (faster) | | Typical Capacity | Very High | High | High | | Transfer Speed | Good | Very Good | Very Good | | Latency / Access Time | High | Medium (rotational latency) | Medium | | Physical Robustness | Very good if stored properly | Sensitive to shocks | Sensitive to shocks | | Affected by Magnetic Fields | Yes | Yes | Yes | ### 1.3 Advantages and Disadvantages - Advantages of Magnetic Tape: - Low cost per byte - High capacity for archiving - Robust technology for long-term storage - Disadvantages of Magnetic Tape: - Slow sequential access - Impractical to update individual data - Sensitive to magnetic fields - Advantages of HDDs: - High capacity and good transfer speed - Mature technologies for servers and mass storage - Disadvantages of HDDs: - Moving parts that can fail - Rotational latency (wait time for the sector to pass under the head) - Sensitive to shocks and magnetic fields Did you know that magnetic tapes are still used in large data centers for archiving because they are very inexpensive per gigabyte and stable long-term? ### 1.4 Real-World Uses and Examples - Magnetic Tapes: long-term backups, government or banking archives, batch processing (mass invoice generation outside peak hours). - HDDs in Servers: website hosting, databases, and systems requiring large storage capacity. - Portable Hard Drives: home backups and transport of large data volumes. ## 2. Flash Memory and Cards (Solid-State Technology, Excluding SSDs) ### 2.1 What is Flash Memory? Flash memory is a type of non-volatile memory based on transistor cells that can retain an electrical charge to represent bits. It has no moving parts, which makes it durable and compact. > Definition: **Flash memory** is non-volatile memory that stores data in transistor cells, allowing information to be retained without power. ### 2.2 Common Types of Flash Media and Their Uses - **USB Flash Drive (pen drive / flash drive / USB stick)**: a removable unit that connects via USB to transport files, perform quick backups, or use as a security key (dongle). - **SD Cards (Secure Digital)**: used in cameras, older phones, tablets, drones, and video recorders. - **XD and CFast Cards**: specialized cards for high-end digital cameras or professional cameras. Comparison Table: Flash Memory | Feature | USB Flash Drive | SD Card | CFast / XD | |---|---:|---:|---:| | Physical Size | Compact | Very Small | Very Small | | Moving Parts