Chapter 4: Business Hardware

Oz (5th 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 (109 or TB or 1012)

• 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