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CSC 1113 – Introduction to Computers
LECTURE NOTES – CHAPTER 4
I. MEMORY VS. STORAGE CIYF 4.
As mentioned in Chapter 1 of this Instructor’s Manual, an understanding of the differences between memory and storage is critical in our quest to engender computer fluency in our students. Understanding memory and storage is so important that you will want to spend as much time on this topic as is necessary to achieve this goal. Teaching Tip : To set the stage for this lecture, it is often helpful to use an analogy to relate new terminology and concepts to things students already find familiar. Try using this analogy or one of your own to begin the lecture: Analogy : Think of RAM as being analogous to your desk or workspace. Describe the analogy as follows: When you sit at your desk and write a letter, a certain amount of space is needed for your tablet, pen, and address book. If you want to have a clock and a CD player on your desk, you will need a bit more space in which to work. The more items you place on your workspace, the more cramped it gets. You can remove items from your workspace, or you can get a bigger desk. RAM is kind of like this: it gives the computer space to put things where it can quickly get to them. Continue with this analogy by relating hard drive space to the file cabinets located next to your desk. You can retrieve files from the filing cabinets at any time, but they are not readily at hand. The number of files you pull from the filing cabinet to place on your desk is dependent on how much space you have on your desk. Remember that your desk holds things other than your files. You may have a video camera on the desk, paint brushes and paints, and a dictionary. All of these items take up space on the desk. Some may need to be put away so that you can make room to work. Explain that mass storage and auxiliary storage are terms that refer to all of the various types of media on which a computer system can store software and data.
A. Why Is Storage Necessary?
Describe the difference between volatile and nonvolatile memory. List the reasons why computers do not use memory to store their files, including the fact that storage is nonvolatile and cheaper than RAM, and that it provides a safe place to back up files. Explain the importance of saving data files on a regular basis. Class Exercise : To emphasize the distinction between memory and storage, create two columns on the board labeled Memory and Storage. Ask students to recall their reading assignment for this chapter. Encourage them to help you create a list of pros and cons. What would you use memory for? What would you use storage for? II. STORAGE DEVICES CIYF 4. Explain that storage devices are categorized by their various features. Define each of these characteristics as they relate to storage devices:
Chapter 4 Lecture Notes
A. Read/Write Media vs. Read-Only Media
CD-RW drives allow computers to perform writing (output) as well as reading (input) operations, whereas CD-R devices allow the computer to read only.
B. Sequential vs. Random-Access Storage
This describes the method used to access the information on the device. Relate sequential storage devices to a tape backup, where you must move sequentially through the tape to find a specific piece of data. Random-access devices go directly to the requested data without having to go through a sequence.
D. Storage Technologies: Magnetic and Optical
Compare and contrast magnetic storage media and optical storage media, referring students to Figure 4.5, and explain the storage capacity of each. Define the role of a read/ write head and the operations of reading and writing. Address the use of combination storage devices called magneto-optical (MO) drives. Class Exercise : Refer students to the TechTalk sidebar regarding the spellings of disk and disc. What do they think? Does the spelling matter any more?
C. The Storage Hierarchy
Describe the three locations in the storage hierarchy: online (primary) storage, near- online (secondary) storage, and offline (tertiary) storage. Class Exercise : Lead students in a discussion of the three different types of storage. Ask them to discuss situations in which each of the types of storage would be most appropriate.
D. Capacity of Storage Devices
One of the reasons students often confuse memory and storage is because they are both measured in bytes. Take this opportunity to reiterate that memory is volatile and storage is nonvolatile. Web Link : Encourage students to visit Acronyms Online and view the Byte Chart (acronymsonline.com/acronyms/byte_chart.htm). Point out that the width of a “word” is generally only 32 bits (depending on hardware) and that the text of a thirty-volume encyclopedia would use about 1GB ASCII storage.
E. Speed of Storage Devices (Access Time)
Discuss the fact that the one characteristic most computer users are concerned with is a storage device’s performance , the speed with which it retrieves data. This speed is called access time. Using Figure 4.7, emphasize that however fast a storage device may be, it will always be slower than RAM. Differentiate between nanoseconds (ns) and milliseconds (ms). Describe the uniqueness of solid state disks (SSDs). Web Link: If students want more information about solid state disks (SSDs), encourage them to visit Raco Industries (www.racoindustries.com/pshcmem.htm) for an image of an SSD and an SSD drive.
Chapter 4 Lecture Notes
D. Formatting: Preparing Disks for Use
Teaching Tip : A good understanding of how disks write data will give students a head start in understanding how an operating system works. It might be helpful to use analogies to describe the physical structure of a disk and the process of formatting. Analogy : A good analogy to describe what happens during a disk format is to think about a developer building a new subdivision out in the country. An unformatted disk is like a parcel of land with nothing on it but trees, rocks, and streams. To prepare the property for use, the developer will survey it, divide it into lots, build roads, and draw a map. This action is similar to the process of formatting. The developer puts a map of the development on the wall of his construction trailer. This map is analogous to the File Allocation Table (FAT). Because some of the lots may be unusable, they are crossed off the map so that they won't be sold. These might be considered in the same way as bad sectors. As people start purchasing the lots, the developer records the name of the individual who now owns the lot. Point out that most disks today are sold preformatted , which means they are ready to receive data. IV. HARD DISKS CIYF 4. Hard disks are by far the most important online storage medium in a computer system. As you describe the physical features of a hard disk, refer to Figure 4.14.
A. Why Are Hard Disks Needed?
Explain to students that the size of software programs and their associated data files is far greater than the storage capacity of a floppy disk. Hard drives were optional at one time, but they are necessary today.
B. How Hard Disks Work
Using Figure 4.15, explain that a hard disk works by moving the read/write head across the surface of the disk as it spins. Explain that the term head crash refers to damage sustained by the hard disk. Define tracks , cylinders , and partitions , using Figure 4.16 as a model. Class Exercise : Lead students in a discussion of hardware reliability, referring to the TechTalk sidebar “Mean Time Before Failure.” At one time, hard drives failed on a regular basis, so measuring the reliability in hours made sense; however, the MTBF is now is expressed in hundreds of thousands of hours and is a fairly worthless number. Today’s hard drives typically last 3-5 years. Typically, a computer will be obsolete by the time the hard drive wears out. This does not mean that hard drives do not fail. Some fail because they were not made right or their contents had defects: You can buy a hard drive that will fail in a month, 6 months, a year. Emphasize that backups are crucial. Hard drives are better-made and more reliable today, but they can still fail.
C. Factors Affecting Hard Disk Performance
Briefly discuss the factors that affect hard disk performance, positioning and transfer performance.
Chapter 4 Lecture Notes
D. Hard Disk Interfaces
Describe the role of a hard disk controller. Assure students that they need not remember all of the acronyms used in this section.
- Discuss this interface, using the terms Integrated Drive Electronics (IDE), ATA (AT attachment), and IDE/ATA.
- Explain the current standard, the IDE/ATA interface , using the terms entry-level drives , Fast IDE , Fast ATA , and ATA-.
- Describe the newer version of the IDE/ATA standard using the terms Ultra DMA/66, ATA-5, and Ultra DMA/.
- Discuss Small Computer System Interface (SCSI), Ultra3 SCSI, and Ultra160 SCSI.
E. Disk Caches: Improving a Hard Disk’s Performance
Explain that hard disk drive performance can be improved by utilizing a type of RAM called disk cache. Use Figure 4.17 a-c to illustrate the point.
F. RAID Devices: Protecting Against Hard Drive Failure
Define RAID as a device that groups two or more hard disks that contain exactly the same data for the purpose of fault tolerance and performance. RAID devices are not necessary for PCs, but are often used for Web servers. Web Link : Encourage students to visit the Advanced Computer & Network Corporation’s tutorial “RAID Technology” (www.acnc.com/raid.html).
G. Removable Hard Disk
Explain that removable hard drives are very similar to the Zip disks discussed previously. They are often used for data archiving and data backup. Refer to Figure 4.19 as an example of a removable hard disk.
H. Internet Hard Drives
Ask students if they use a hard drive on the network at school as a storage place for their papers and documents. Explain that this is similar to an Internet hard drive, which is storage space accessible from the Internet. Web Link : Ask students to visit the XDrive Web site (www.xdrive.com/index.jsp) for more information about and examples of Internet storage technology. V. VARIOUS STORAGE MEDIA CIYF 4.
A. Magnetic Tape
Teaching Tip : If you have managed to accumulate a sample magnetic tape in your box of demonstration hardware, show it now as you discuss the features of various types of tape.
Chapter 4 Lecture Notes of September 11, 2001. Discuss the concept of redundancy and how it could be important in the event of future terrorist attacks.
A. FMD-ROM
Define FMD-ROM (florescent multilayer disc-read only memory). Describe the difference between a standard DVD and an FMD-ROM disc.
B. Solid State Storage Systems
- Define PC card , also referred to as a PCMCIA card , and discuss each of the three types: Type I PC cards , Type II PC cards , and Type III PC cards.
- Define and describe the most common use for flash memory cards. Briefly discuss flash memory reader , SmartMedia , CompactFlash , and Memory Stick memory cards.
- Describe the advantages of smart cards and digital cash systems.
C. Enterprise Storage Systems
Review enterprise storage systems and the use of a storage area network (SAN). VII. CHAPTER REVIEW CIYF 4.X Web Link: Refer students to www.prenhall.com/cyif2004 for a review of the chapter, to answer the questions, and to complete the exercises and Web research questions. Takeaway Points : Ask students to recall the objectives identified at the beginning of this lesson. Tie the initial objectives with the essential lecture points that met the objectives. Objective : Distinguish between memory and storage. Memory is volatile and costly. Storage is slower and less costly. Objective : Discuss how storage media are categorized. Storage media are categorized by the types of operations they perform, their capacity, and their access speed. Objective : Explain how data is stored. Disks store data in tracks. Tracks are divided into sectors. Sectors are divided into clusters. A cluster is the basic unit for data storage. Hard disks and floppy disks store data the same way. Hard disks have multiple platters. Objective : List two ways to measure a storage device’s performance. A hard disk’s performance is measured by its positioning performance and its transfer performance. Objective : Explain the uses of removable disks. Removable disks are often used for data archiving and data backup. Objective : List the performance characteristics of hard drives. The two leading hard drive interfaces are IDE drives and SCSI drives. IDE drives are cheaper. SCSI drives are faster and offer greater storage capacity.
Chapter 4 Lecture Notes Objective : List and compare the various optical storage media available for personal computers. CD-ROM drives are standard equipment today. CD-R is read only; CD-RW is readable and writable. DVD-ROMs offer more storage capacity than CD-ROMs. Objective : Identify the types of new storage technologies, such as FMD-ROM discs, solid state storage devices, and enterprise storage systems. Solid state storage devices such as flash memory offer several advantages over older storage technology. RAID systems are used as enterprise storage.
