Dzta Scorage be altered many times a second. However, in those applications in which alterations can be controlled to a reasonable level, such as in digital cameras and smartphones, flash memory bas become the mass storage technology of choice. Indeed, since ash menory is nat sensitive to physical shock in co trast to magnctic and optic systems), i is now replacing other mass storage techmologies in portable applicatioas such as laptap conputess. . Whhat factor s allow CD DVD, and Blu-ray diska all to be read by t e amc davc? S. What ad e do flash drives haveover the other mass storage thissction? ystmis 6. What azzantages coatinue to make magnetic hard disk drives Flash memary devices called flash drives, with capacities of hundreds of GBs, are avalable for general mass storage applications. Tbese units are pack- aged in ever smaller plastic cases with a removable cap on one end to protect the unit's electrical connector wben the drive is off-line. The high capacity of these portable units as well as the fact that they are easily connected to and disconnected from a computer make them ideal for portable data storage Howev er, the vulnerability of their tiny storge chambers dictates that they are not as reliable as optical disks for truly long-term applications coipotitav 4 Representing Information as Bit Patterns Larger flash mety devices called SSDs (solid state drives) ae explic- itily designed to take the place of magnetic hard disks. SSDs compare favor ably to hard disks in theit resilience to vibrations and physical shock, theair quiet operation due to no moving parts), and their lower access times. SSDs remain more expensive than hard disks of comparable size, and thus, are still considered a high-end option when buying a desktop coanputea. For mobile applications, such as laptops and smartphones, SSDs have the clear advantage SSD sectos sufefom the oe limited lifetime of all lash meory nologics, but the usc of wear-leveling techniques can reducc the impact of this by relocating fiequently altezed data blocks to fresh locations on the dhive Another application of flash technology is found in SD Secure Digital) memory cards (or just SD cards). These provide up to two GBs of storage and are packaged in a plastic rigged wafer about the size of a postage stamp (SD cards are also available in smaller mini and micro sizes.) SDHC (High Capacity) mery cards can provide up to 32 GBs arnd te next gemeation SDXC (Extended Capaciry) memory cards can exceed a TB. Given their compact physical size, these cards convenieatly slip into slots of small electronic devicas. Thus, they are ideal for digital camic players, car 3 Questions & Exercises 1. What is gained by increasing th rotation speed of a disk or CD? 2. When recording data on a multiple-disk storage system, should we fill a complete disk surface before starting on another on another cylinder? being updated be stored on a magnetic disk instead of a CD or 3. Why should the data in a reervation system that is constantly DVD? 42
