Other forms of mass storage

Chapter Other forms of mass storage

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • number of arcs called sectors. A cylinder is the set of equal-radius tracks on all theplatters in the drive. Tracks and sectors are set up on the hard drive during the ini-tial formatting process. There are also data units called clusters. These are unitsconsisting of one to several sectors, depending on the arrangement of data on theplatters. Figure 33-2B is a face-on view of a single hard-disk platter, showing a trackand one of its constituent sectors.The average new computer hard-drive data storage capacity roughly doublesevery year, and thus increases by about three orders of magnitude per decade. Atthe end of the year 2000, during the holiday computer-buying season, a new desktopmachine had between 10 and 100 GB of hard-drive capacity. By the end of the year2010, if trends continue, these figures will be approximately 1000 times greater—arange of 10 to 100 TB. Do petabyte and exabyte machines mentioned a few para-graphs ago seem out of this world, impossible, or ridiculous? Extrapolate. Chancesare good that you will live to see them.When you buy a computer, whether it is a desktop, notebook (also called laptop),or portable (also called handheld) unit, it will have a hard drive built in. The drive comesinstalled and formatted. Most new computers are sold with several commonly used pro-grams preinstalled on the hard drive. Some computer users prefer to buy new comput-ers with only the operating system, by means of which the programs run, installed; thisfrees up hard-drive space and gives the user control over which programs to install (ornot to install).Other forms of mass storageThere are several types of mass storage (besides the hard drive) in which data canbe kept in large quantities. Computer experts categorize mass storage in two ways:access time and cost per megabyte. In general, the less the access time (that is, thefaster the storage medium), the greater the cost per megabyte. The fastest massstorage media usually have the lowest capacity.Flash memoryFlash memory is an all-electronic form of storage that is useful especially in high-level graphics, big-business applications, and scientific work. The capacity is compa-rable to that of a small hard drive, but there are no moving parts.Because there are no mechanical components, flash memory is faster than any othermass-storage scheme. PC cards (also called PCMCIA cards) are credit-card-sized, re-movable components, some of which are designed to serve as removable flash memory.Disk mediaMagnetic diskettes, also called (imprecisely) “floppies,” are 3.5 inches in diameterand enclosed in a rigid, square case about 4 millimeters thick. They can be inter-changed in seconds, so there is no limit to how much data you can put on them. Buttheir capacity, individually, is limited. A full-wall bookcase of diskettes could holdmore work than you’d create in your lifetime.Zip and Jaz disks (trademarks of Iomega Corporation) are slightly larger than 3.5-inch diskettes in physical dimension, but vastly larger in storage capacity. The original628 Computers and the Internet