Understanding Storage Media & File Representation: Non-Volatility & Magnetic Disks - Prof., Study notes of Computer Science

Download Understanding Storage Media & File Representation: Non-Volatility & Magnetic Disks - Prof. and more Study notes Computer Science in PDF only on Docsity! CS201 Lecture-5 Non-Volatility: Storage media are non-volatile: When power to the device is shut off, data stored on the medium remains. This is in contrast to most types of memory, which are volatile. Random vs. Sequential Access: Random access (direct access): data can be retrieved in any order, independent of its physical location (most types of storage media). Sequential access: data can be retrieved only in the same sequence in which it is physically stored (magnetic tape). Advantages of Removable media: Easily replaceable with empty storage device Transportability Backup Security Logical vs. Physical Representation: Logical file representation refers to the user’s view of the way data is stored (filename, folders, etc.). Physical file representation is the actual physical way the data is stored on the storage media as viewed by the computer. Magnetic Disk Systems: Magnetic Disk: A storage medium that records data using magnetic spots on disks made of flexible plastic or rigid metal. Magnetic disks are the most widely used storage medium in computers today. A magnetic disk is covered in a very thin film (less then 1µm thick) of a magnetic material (ferrous oxide, phosphor-nickel, or something of the like), on both sides. Data is stored by magnetizing particles on the storage medium. Two common types:  Floppy disks  Hard disks Floppy Disks and Drives: Floppy disk characteristics: Typically 3½ inches in diameter Typically hold 1.44 megabytes Inserted into floppy disk drive to be read from or written to Disk is divided into tracks, sectors, and clusters. The disk’s file directory keeps track of the contents of the disk so files can be retrieved (by filename) at a later time. Hard Drive: Inside hard drive disks are mounted, along with up to 20 other disks in parallel, upon an axis. The disks thus form a cylinder called a disk pack. There is typically a gap of around 1cm between each disk in the pack. This allows space for the read / write heads to pass between the disks. Each side of every disk requires a Read / Write head. Thus a 20 disk pack will need 40 heads to function properly. Bumping PC when disk is being accessed or dust or other obstacles on a hard-disk system can cause a head crash and damage the surface of the disk. When the power is on, disks spin at around 5400 and 15,000