Storage Devices & Measuring Memory Capacity

Secondary storage (auxiliary or external storage) refers to non-volatile physical hardware media designed to store digital programs, documents, operating systems, and multimedia permanently for future retrieval. • Why Secondary Storage is Indispensable: 1. Non-Volatility: Retains stored data indefinitely without requiring continuous electrical power. 2. Immense Storage Capacity: Can hold hundreds of Gigabytes or Terabytes of software and files at a fraction of the cost of RAM. 3. Portability: Removable media (flash drives, memory cards, external drives) allow easy transport of data between different computers.

• 1. Magnetic Storage Media: - Operates by magnetizing tiny iron oxide particles on spinning metallic platters to represent binary 1s and 0s. - Hard Disk Drive (HDD): Primary mass storage for desktop PCs. Contains spinning platters rotating at 5,400 to 7,200 RPM and mechanical read/write heads. - Magnetic Tape: Used by banks and archives for cheap, long-term sequential data backup. • 2. Optical Storage Media: - Polycarbonate plastic discs read and written using laser beams. A laser burns microscopic pits (indentations) and lands (flat areas) representing binary data: * CD (Compact Disc): Storage capacity of approx. 700 MB. * DVD (Digital Versatile Disc): Storage capacity of 4.7 GB (single-layer) to 8.5 GB (dual-layer). * Blu-ray Disc (BD): Uses a shorter blue-violet laser to store 25 GB to 50 GB of high-definition video. • 3. Solid-State Storage Media (Flash Memory): - Uses non-volatile silicon flash microchips with ZERO moving mechanical parts: * Solid-State Drive (SSD): Super-fast, silent storage replacing HDDs in modern laptops. * USB Flash Drive (Pen Drive): Compact, pocket-sized storage connecting via USB ports. * SD Memory Card: Tiny cards used in smartphones, digital cameras, and dashcams. • 4. Cloud Storage: - Storing files on remote enterprise server farms managed by providers (Google Drive, Microsoft OneDrive, Dropbox) accessible over the Internet from any connected device.

The computing world is rapidly transitioning from mechanical HDDs to electronic SSDs: • Speed Comparison: SSDs read and write data electronically at speeds exceeding 500 to 3,500 MB/s, booting Windows in 10 seconds. HDDs are constrained by spinning platters and read heads (100 to 150 MB/s). • Physical Durability: HDDs are highly vulnerable to physical shock. Dropping a running laptop can cause a head crash, destroying the platters. SSDs have no moving parts and easily survive physical drops and vibrations. • Noise and Energy Consumption: SSDs are completely silent, produce minimal heat, and consume less battery power. HDDs emit humming noises and drain laptop batteries faster.

Digital computers represent all data using the binary number system (base 2): • Bit (Binary Digit): The absolute smallest unit of digital data, holding a single 0 or 1. • Nibble: A group of 4 bits (e.g. 1010). • Byte: A group of 8 bits. Represents a single alphanumeric character (e.g. typing 'G' uses 1 Byte = 8 bits). • Kilobyte (KB): 1,024 Bytes. • Megabyte (MB): 1,024 Kilobytes (approx. 1 million bytes; holds a typical MP3 song). • Gigabyte (GB): 1,024 Megabytes (approx. 1 billion bytes; holds an HD movie). • Terabyte (TB): 1,024 Gigabytes (approx. 1 trillion bytes; large external backup drive). • The 1,024 Factor: Because computers operate on binary powers of 2 (2¹⁰ = 1,024), each unit is 1,024 times larger than the previous unit!