5.1.2 Storage Device Facts
Hard disk drive (HDD)
A hard disk is a thick magnetic disk encased in a thicker protective shell. A hard disk consists of several aluminum platters, each of which requires a read/write head for each side. All of the read/write heads are attached to a single access arm to prevent them from moving independently. Each platter has circular tracks that cut through all of the platters in the drive to form cylinders. The spinning of the platters if referred to as revolutions per minute (RPM). Common RPM speeds: -5400 rpm (inexpensive SSD) -7200 rpm (good quality SSD) -10,000 rpm (expensive SSD) Some of the advantages of hard disks are: -They have lots of storage (starting at 16 GB up to several TB) -The are way faster than floppy disks -The cost per MB is cheap. Disadvantages of hard disks are: -Many hard disks are internal devices, though you can get external enclosures -They are prone to failure -They are vulnerable to physical damage (when dropped)
Solid State Drive (SSD)
A solid state drive is a flash device with a storage capacity similar to a small hard drive. Solid state drives are used as replacements for hard disk drives for storing OS, application, and data files. Advantages: -faster than hard drives -no moving parts, last longer -lower power consumption than hard drives -less susceptible to physical damage and immune from magnetic fields. -smaller and lighter than hard drives The main disadvantage of an SSD is its cost. An SSD costs so much more compared to an HDD.
Flash devices
Flash memory cards store information using programmable, non-volatile flash memory. Advantages: -Memory reprogrammable -Can retain content without power -Optimal for use in devices like cameras -Highly portable -Larger capacity than CDs and DVDs -Relatively fast memory access. Disadvantages: -Their storage capacity is not yet comparable to the capacity of modern hard disks -Different memory card formats require different readers
Optimal
Optical discs such as CDs, DVDs, and Blu-ray discs are a storage medium that uses lasers for both reading and writing information. Optical discs store information through pits in their reflective coating. As the disc spins, the optical drive sends laser optics to the disk, and receives the stored information through the deflected output. Advantages: -Great for music and video -portable and universal -cheap -you can buy discs that are recordable -they have a long shelf life and are relatively sturdy -Blu-ray discs can store a large amount of data (25 GB or more depending upon the format) Disadvantages: -Slower than hard disks -small capacity (650 MB for CDs, 4.7 GB for DVDs) -some compatibility issues between disc formats and readers
Tape drive
Tape drives (also called digital linear tape or DLT drives) store data on magnetic tapes. Tape drives are most commonly used for data backups, such as taking a backup of all hard drives in a system. Advantages: -Tapes can store large amount of data. Range from 10 GB to 800 GB per tape -Tapes can be changed, allowing you to save data from different sources on the same drive -Tape are relatively inexpensive and small enough for long term storage. Disadvantages: -Access to data on tape is typically slower than reading or writing to other storage types, making them not well suited for instant interactive access -Data must be read from tape sequentially. The tape must be cued to the exact location on tape when data must be retrieved.
