Chapter 4: Business Hardware Oz (5 th edition)

Storage Media Data an programs must be stored on nonvolatile medium –Data is retained even when not powered –Programs are copied from storage media into the computer’s memory Storage devices differ in technology used to maintain data and physical structure Early PCs had a single floppy drive Storage media versus storage device

Important Characteristics of Storage Devices/Media Mode of access –Sequential –Direct Representation of bits –Magnetic ( iron oxide dots magnetized two ways) –Optical (surface reflects light in two ways –IBM’s Millepede technology (pits are burned in plastic to represent a 1, no pit a zero; heat the plastic and you erase the pit) –Electronic (current flowing/current not flowing)

Modes of Access Figure 4.6: Sequential and direct access

Numerical Characteristics of Storage Media/Devices Storage capacity –Measured in GB (10 9 or TB or ) Access speed (time it takes for device to locate data on the medium) Transfer rate (time the device requires to move data from the medium to main memory); CD transfer rates as 60X (60 * 150,000 bits/sec) Density (bytes or bits per square inch) Rotational speed (magnetic disk) in rotations per minute (5400 – 15,000 is current range) Cost ratio is calculated by dividing storage capacity by cost (e.g., if a 300 GB drive costs $200, then cost ratio 200/300 or $.67 per GB)

Types of Media & Devices Magnetic tape Magnetic disk Optical tape Optical disk –CD-ROM, CD-R, and CD-RW –DVD-R and DVD-RW Flash memory –Cards –Thumb drives or USB flash drive

Magnetic Tapes Magnetic tapes: similar to tape recorders and VCRs –Provide lowest cost (bytes per dollar) –Can backup all data –Takes long time to copy from tape –Unreliable after a long period of time

Magnetic Disks Magnetic disk: most widely used storage medium Hard disk: stack of several aluminum platters installed in same box that holds CPU –Stores up to 500 GB of data –External hard disks connect to computer through USB port

Optical Discs Optical disc: recorded by treating disc surface to reflect light in different ways Compact discs: available as read-only, recordable, and rewritable DVDs: store 4.7 GB per side Optical discs are slower than hard disks

Optical Tape Optical tape uses same technology as optical discs to store and retrieve data Bits are organized sequentially like tape Used in digital video camcorders

Flash Memory Flash memory: memory chip that can be rewritten and holds content without power Available as memory card and USB drive Solid state disk: storage media that does not have latency time

Business Considerations in Evaluating Storage Media When purchasing storage devices managers must consider: –How the data is used –Capacity of the device –Speed and cost –Reliability and portability

Business Considerations In Evaluating Storage Media Figure 4.7: Characteristics of storage media for business purposes