Reference: Chp 6 Introduction to Computers by Peter Norton Lecture Storage Devices Reference: Chp 6 Introduction to Computers by Peter Norton

(Reference : DC2009 book chapter slides) Storage Devices (Reference : DC2009 book chapter slides)

Storage What is storage? Also called secondary storage Holds data, instructions, and information for future use Storage medium is physical material used for storage Also called secondary storage p. 354 - 355 Fig. 7-1 Next

Storage How does volatility compare? ON OFF Storage medium is nonvolatile—contents retained when power is off Memory is volatile—holds data and instructions temporarily ON OFF Memory (most RAM) (chips on motherboard) Screen Display Display appears Display disappears Volatile Data and instructions available to user Data and instructions erased Storage Medium (hard disks, CDs, DVDs, USB flash drives, etc.) Nonvolatile Contents available to user Contents retained p. 355 - 356

Storage What is a storage device? Hardware that records and retrieves items to and from storage media Reading Process of transferring items from storage media to memory Writing Process of transferring items from memory to storage media p. 356

Magnetic Disks e.g. hard disk, floppy disk Sector stores up to 512 bytes of data e.g. hard disk, floppy disk What are tracks and sectors? Track is narrow recording band that forms full circle on disk p. 357 Fig. 7-5

Hard Disk What is a hard disk? High-capacity storage Consists of several inflexible, circular platters that store items electronically Components enclosed in airtight, sealed case for protection p. 358 Fig. 7-6

Hard Disk What is a cylinder? platter What is a cylinder? track Vertical section of track through all platters sector Single movement of read/write head arms accesses all platters in cylinder read/write head platter sides p. 360 Fig. 7-9 cylinder

Hard Disk

Physical layout of a magnetic disk Figure 5-6 Physical layout of a magnetic disk

Surface organization of a disk Figure 5-7 Surface organization of a disk

Magnetic Disks Access time

Seek Time: In order to read or write data in a particular place on the disk, the read/write head of the disk needs to be physically moved to the correct place. This process is known as seeking, and the time it takes for the head to move to the right place is the seek time. Rotational delay or rotational latency: It is the time required for the addressed area of a computer's disk drive to rotate into a position where it is accessible by the read/write head.

Floppy Disk What is a floppy disk? Portable, inexpensive storage medium (also called diskette) Thin, circular, flexible film enclosed in 3.5” wide plastic shell p. 365 Fig. 7-16

Optical Discs e.g. CDROM, DVD, etc. What are optical discs? Push button to slide out tray e.g. CDROM, DVD, etc. What are optical discs? Flat, round, portable metal discs made of metal, plastic, and lacquer Insert disc Can be read only or read/write Push same button to close tray Most PCs include an optical disc drive p. 366 Fig. 7-17

Optical Discs What is a CD-ROM? Compact disc read-only memory Cannot erase or modify contents Typically holds 650 MB to 1 GB Commonly used to distribute multimedia and complex software p. 369 Fig. 7-22

Ranges from 48X to 75X or faster X is 150 KBps (KB per second) Optical Discs What is the data transfer rate of a CD-ROM drive? Ranges from 48X to 75X or faster 75X 75  150 KBps = 11,250 KBps or 12.25 MBps X is 150 KBps (KB per second) 48X: 48  150 KBps = 7,200 KBps or 7.2 MBps p. 369

Optical Discs What are CD-Rs and CD-RWs? Must have CD recorder or CD-R drive CD-R (compact disc-recordable) —cdisc you can write on once Cannot erase disc’s contents CD-RW (compact disc-rewritable) —ceerasable disc you can write on multiple times Must have CD-RW software and CD-RW drive p. 370

Magnetic Tape What is magnetic tape? Magnetically coated plastic ribbon capable of storing large amounts of data at low cost Primarily used for backup p. 374 Fig. 7-27

Magnetic Tape How is data stored on a tape? Sequential access Reads and writes data consecutively, like music tape Unlike direct access — used on hard disks, CDs, and DVDs — which can locate particular item immediately p. 374

Mechanical configuration of a tape Figure 5-8 Mechanical configuration of a tape

Figure 5-13 Making a CD-RW Amorphous, less organized arrangement of atoms Crystalline, more organized arrangement of atoms All CDs and DVDs work by virtue of marks on the disc that appear darker than the background. These are detected by shining a laser on them and measuring the reflected light. In the case of molded CDs or DVDs, such as those bought in music or video stores, these marks are physical “pits” imprinted into the surface of the disc. In CD-Recordable (CD-R) discs, a computer’s writing laser creates permanent marks in a layer of dye polymer in the disc. CD-Rewritable (CD-RW) discs are produced in a similar fashion, except that the change to the recording surface is reversible. The key is a layer of phase-change material, an alloy composed of silver, indium, antimony and tellurium. Unlike most solids, this alloy can exist in either of two solid states: crystalline (with atoms closely packed in a rigid and organized array) or amorphous (with atoms in random positions). The amorphous state reflects less light than the crystalline one does. When heated with a laser to about 700 degrees Celsius, the alloy switches from the original crystalline phase to the amorphous state, which then appears as a dark spot when the disc is played back. These spots can be erased using the same laser (at a lower power) to heat the material to a temperature of 200 degrees C or so; this process returns the alloy to its crystalline state. Most CD-RW makers suggest that one disc can be overwritten up to 1,000 times and will last about 30 years. (Wikipedia: http://en.wikipedia.org/wiki/CD-RW)