1.6 Hard Drives

• Hard Drives are large storage devices meant for long term use, with the main function of storing data, operating system, software, documents, music, videos, pictures.
• The storage size of a Hard Drive is measured in bytes.
• Hard Disk Drives (HDD) use memory that writes data onto disks within the components via magnets, are usually larger in storage, and are less stable.
• Solid Slate Drives (SSD) use flash memory that electronically adds and removes data to a chip, are more expensive, much faster for reading and writing, and are less stable.
• Hard Drives come in two physical sizes: 2.5-inch (Small Form Factor - SFF) or 3.5-inch (Large Form Factor - LFF).
• Hard Drives can be connected via interfaces such as Serial ATA (SATA), Serial-attached SCSI (SAS) and there are also SSD specific ones.
• Hard Drives have different read and write speeds, with Hard Disk Drives (HDD) containing magnetic disks that rotate for Read & Write, measured in RPM: Revolutions per Minute, and Solid Slate Drives (SSD) using controllers (embedded processor) for Read & Write, with speed measured in bytes per second.
• The storage capacity of a modern hard drive is made possible by recording data as magnetic patterns formed by microscopic magnetized metal grains, allowing for a high density of information to be stored.
• Writing data onto the disc involves converting bits into electrical current, which generates a magnetic field strong enough to change the magnetization of the metal grains.
• The magnetic reader in a hard drive reads the magnetic patterns and translates them back into a usable form of data.
• Areal density, or the number of bits that can be stored in one square inch, has significantly increased over time through innovations in technology, such as shrinking the reader and writer, using mathematical algorithms to filter out interference, and controlling thermal expansion of the head.
• Changing the direction of recording from longitudinal to perpendicular has allowed for higher areal densities.
• Heat assisted magnetic recording, where a laser is used to reduce magnetic resistance, has also increased storage capacity.