Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives...

Understanding Computers Ch.4 1

Chapter 4

Storage


Learning Objectives

Explain the difference between storage systems and memory.

Name several general properties of storage systems.

Identify the two primary types of magnetic disk systems and describe how they work.


Learning Objectives, Cont’d.

Discuss the various types of optical disc systems available and how they differ from each other and from magnetic systems.

List at least three other types of storage systems.

Summarize the storage alternatives for a PC, including which storage systems should be included in all PCs and when the other systems would be appropriate.


Overview This chapter covers:

Common characteristics of storage systems

Magnetic disk storage systems

Optical disc storage systems

Other types of storage, such as flash memory, magnetic tape, remote storage, and smart cards


Properties of Storage Systems: Storage Devices and Media

Involve two physical parts: a storage device and a storage medium.

Can be internal (located inside the system unit), or external (located outside the system unit).

Storage devices are identified by names and/or letters (e.g. “C” for first hard drive).


Properties of Storage Systems: Non-Volatility

Storage media are non-volatile:

When power to the device is shut off, data stored on the medium remains.

This is in contrast to most types of memory, which are volatile.


Properties of Storage Systems: Removable vs. Fixed Media

Fixed media: typically faster and less expensive.

Removable media: unlimited capacity and can be easily transported and secured.


Properties of Storage Systems: Random vs. Sequential Access

Random access ( direct access ): data can be retrieved in any order, independent of its physical location (most types of storage media).

Sequential access: data can be retrieved only in the same sequence in which it is physically stored (magnetic tape).


Properties of Storage Systems: Logical vs. Physical Representation

Logical file representation refers to the user’s view of the way data is stored (filename, folders, etc.).

Physical file representation is the actual physical way the data is stored on the storage media as viewed by the computer.


Magnetic Disk Systems

Magnetic disks are the most widely used storage medium in computers today.

Data is stored by magnetizing particles on the storage medium.

Two common types: Floppy disks Hard disks


Floppy Disks and Drives

Floppy disk characteristics

Typically 3½ inches in diameter.

Typically hold 1.44 megabytes.

Inserted into floppy disk drive to be read from or written to.


Floppy Disks and Drives, Cont’d. Disk is divided into tracks, sectors, and clusters.

The disk’s file directory keeps track of the contents of the disk so files can be retrieved (by filename) at a later time.


Floppy Disks and Drives, Cont’d.

Using floppy disks Must be inserted into the proper drive in the proper

direction. Should not be removed when the disk is being

accessed.

High-capacity removable magnetic disks and drives Zip disks (750 MB) SuperDisks (240 MB)


Hard Disk Drives Hard drive characteristics

Metal disk onto which data is stored magnetically.

Disks are usually permanently sealed inside the hard drive—allows faster speeds and storage of more data than removable systems.

Can be internal or external.


Hard Disk Drives, Cont’d. Hard drive characteristics, cont’d

Organized into tracks, sections, clusters, and cylinders (the collection of tracks located in the same location on a set of hard disk surfaces).

Read/write head doesn’t touch the surface of the disk.

Bumping PC when disk is being accessed or dust or other obstacles on a hard-disk system can cause a head crash and damage the surface of the disk.


Hard Disk Drives, Cont’d. Disk access time.

Factors: seek time, rotational delay, data movement time

Can use multiple partitions.

Disk cache—strategy for speeding up system performance.

Hard drive standards (EIDE, SCSI, Fibre Channel, USB) .


Hard Disk Drives, Cont’d.

Portable hard drive systems

Offer large storage capacities and portability.

Either entire drive or just hard disk cartridge is transported.


Hard Disk Drives, Cont’d.

Storage systems for large computer systems and networks

Storage servers containing racks of hard drives.

Network attached storage (NAS).

Storage area networks (SANs).

RAID (for increased performance and/or fault tolerance).


Optical Disc Systems

Laser beams write and read data packed at very tight storage densities, many times finer than that of a typical magnetic disk.

Are typically 4½-inch discs, but can be a variety of shapes and sizes.

Data is stored optically on a continuous spiral track.

Can be CDs or DVDs.


Read-Only Discs: CD-ROM and DVD-ROM Discs

CD-ROM discs cannot be written to or erased and typically hold 650 MB (e.g. music CDs).

DVD-ROM discs are similar to CD-ROM discs, but have higher capacity of 4.7 GB to 17 GB (e.g. movie DVDs).

Data is stored by burning pits into the disc surface that can be read using a laser beam.


Recordable Discs: CD-R, DVD-R, and DVD+R Discs

Recordable discs can be written to, but not erased or rewritten.

Burning a CD or DVD permanently records data onto the disc.

CD-R discs are commonly used to store data and for custom music CDs.

DVD-R/DVD+R discs are commonly used for home movies and other high-capacity applications.


Rewritable Discs: CD-RW, DVD-RW, DVD+RW, DVD-RAM, and Blue Laser Discs

Rewritable discs can be used in the same way as magnetic disks—data can be stored and erased as needed.

Phase-change technology is used to record data onto the

disc using reflectivity.

Rewritable discs can be erased by reverting the reflectivity back to the original state.

Blue laser discs are an emerging higher-capacity (23.3 GB) form of optical disc.


Other Types of Storage Systems

Magneto-optical discs

A combination of magnetic and optical technology.

Can store up to 9.1 GB per disk.


Other Types of Storage Systems, Cont’d

Flash memory media

Chip-based storage.

Solid state storage system—has no moving parts, so are more shock-proof and portable than conventional storage systems.

Commonly used with digital cameras, digital music players, handheld PCs, notebook computers, smart phones, etc.



Flash memory media, cont’d.

Common forms of flash memory:

Flash memory sticks.

Flash memory cards—CompactFlash, Secure Digital (SD), MiniSD, MultiMedia (MMC), SmartMedia, and xD Picture cards.

Flash memory drives, such as USB flash drives.


Other Types of Storages Systems, Cont’d

Magnetic tape systems—plastic tape that is magnetized to represent data.

Used primarily for backup and archival purposes (sequential access only).

Read from and written to via a tape drive.

Most tape media are in the form of cartridge tapes, though detachable-reel tapes exist as well.



Remote storage—storage devices that are not directly connected to your PC.

Network storage—accessible through a local network.

Online storage—accessible via the Internet and used for backup, as well as to transfer files to others.



Smart card: credit-card-sized piece of plastic that contains some type of computer circuitry.

Holds less than a few megabytes.

Commonly used to store prepaid amounts of digital cash or personal information.

Smart card readers are attached to a PC or built into a cell phone, keyboard, or other device.



Holographic storage

Uses multiple laser beams to store data in three dimensions.

Stores data in page format.

No moving parts and simultaneous access to all data on a page.


Comparing Storage Alternatives

Factors to consider: speed, expense, portability, storage capacity, and compatibility.

Most PC users require: Hard drive CD or DVD drive Floppy drive Additional devices (flash memory card reader,

etc.) as needed for the devices being used in conjunction with the PC (e.g. digital camera)


Summary

Properties of storage systems

Magnetic disk systems

Optical disc systems

Other types of storage systems

Comparing storage alternatives

Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives...

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