| Answer | Correct Statement |
| 1. T | Storage holds data, instructions, and information for future use. |
| 2. T | A storage medium is the physical material on which a computer keeps data, instructions, and information. |
| 3. T | Density
is the number of bits in an area on a storage medium. Density is the number of bits per unit of length, area, volume, or mass of storage medium. |
| 4. F | A
track is a narrow recording band that forms a full circle on the surface
of the disk. The term sector has 2 meanings. 1. A sector is a wedge shaped section of a disk. 2. A sector is a segment of a track bounded by a wedge shaped section on a disk. This type of sector is the smallest addressable location on a disk, and the smallest storage unit the disk can read from or write to. |
| 5. F | A cluster (or allocation unit) is the smallest amount of disk space that can be allocated to hold a file. |
| 6. F | A typical microcomputer hard drive has multiple platters. |
| 7. T | An external hard disk is a separate, free-standing hard disk that connects with a cable to a port on the system unit. |
| 8. F | CDs and DVDs are not magnetic media. These are often called optical disks because a laser is used to read them. |
| 9. T | Ripping is the process of copying a song from an audio CD and converting it to a digital format. (as in ripping off, stealing) |
| 10. F | Direct access, also called random access, means that the device can locate a particular data item or file immediately, without having to move consecutively through items stored in front of the desired data item or file. |
| 11. T | A solid state device is an semiconductor device. The term solid state was established to contrast transistors and chips from vacuum tubes, which also had no moving parts. Vacuum tubes are not called solid state electronics. |
| 12. T | E-money is a means of paying for goods and services over the Internet. |
1a. What is access time?
Access time is the difference between the time a request for data is issued to a storage device until the time the data is retrieved. Access time is more than just the time required to locate the data.
At lease one hard disk manufacturer measures access time from the time the disk arm begins to move until the data begins transfer.
Access time will vary greatly on a given device depending on the initial conditions and the location of the requested data. Average access time is usually used to characterize the data retrieval performance for a particular device. Programmers and systems analysts attempt to reduce the average access time by thoughtfully designing file structures for the mixture of programs run at that particular computer center. This is particularly important for disk and tape storage systems.
1b. Why is the average hard disk access time faster than the average floppy disk access time?
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A hard disk continuously spins, and spins at a rate much faster than a floppy disk. A floppy disk stops spinning after not receiving requests for reading or writing after some fixed period of time. |
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The coating on a hard disk supports a much higher data density than the coating on a floppy disk. The linear distance required to store a fixed amount of data is less on a hard disk than on a floppy disk. Therefore, for the same rotational speed, it takes less time to read the data from the higher density disk. |
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Some hard drives permit the programmer/ systems analyst to control the location of the file allocation table or directory to reduce the time spent by moving the read/write head between the file allocation table and the file. This is common on main frame hard drives. |
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A floppy disk used with MS DOS or MS Windows is usually structured to have two file allocation tables (FAT) to increase reliability, necessary since the read/write head makes physical contact with the floppy disk which causes wear. Both FATs must be updated when data is written to the floppy disk. Reliability for floppy drive use is considered more important than speed of data access. The read/write head on a hard disk does not make contact with the disk while it is in operation. |
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Some hard drives for main frame computers have a read/write head for each track which eliminates the time required to position a read/write head over the desired track. Some hard drives have multiple read/write heads on a movable arm which reduces the distance the arm must travel before a head is over the desired track. |
2a. What is density?
Density is measured in several ways.
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Volume Density. Bits per unit volume. This applies to the optical cube now in development. | ||||||
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Areal (area) Density. Engineers designing disks measure density for a recording media in bits per unit area. | ||||||
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Lineal Density. Linear density is bits per unit length. Linear
density is often reported in other terms.
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Mass Density. Bits per kilogram. Along with volume density, this is important for space and aviation applications. |
(Lineal and areal are not misspelled. These are the correct technical terms.)
Capacity is the total number of bits or bytes a storage device can store. The capacity is affected by the density, size, and the formatting of the disk. The text gives an example of computing capacity of a 3.5-inch floppy disk.
2 b. What does it mean to say that floppy disk drives are downward compatible but not upward compatible?
A floppy disk drive is "downward compatible" if it can read/write disks formatted using older (lower density) floppies. An older floppy had a capacity of 720 kB, compared to the newer 1.44 MB. Older floppy disk drives cannot read/write floppy disks formatted at higher densities. The 250 MB Zip drive can read and write 100 MB Zip disks. The 750 MB Zip drive can read and write 250 MB Zip disks, but can only read 100 MB Zip disks.
A 720 kB floppy drive cannot read or write at 1.44 MB. A 100 MB Zip disk cannot read or write at 250 MB or 750 MB. A 250 MB disk cannot read or write at 750 MB. These are not upward compatible.
From a practical point of view, it means you need to pay attention to having the capability of copying old data files to newer media as you upgrade system capabilities. If you get two generations out of data, you may end up with not physically being able to retrieve data you spent much time and money to accumulate and organize. [It is hard to find a working punched card reader today!]
3a. Why is a hard disk inside the system unit sometimes called a fixed disk?
A fixed disk is one that is permanently mounted to its disk drive. It says nothing about the whether or not the disk drive is portable, or whether the disk drive is mounted inside or outside the system unit.
The term fixed disk is used to distinguish that disk and disk drive from a drive that uses a removable disk. On main frames, a large removable disk with multiple platters is called a disk pack.
3b. How is an external hard disk different from a removable hard disk?
An external hard disk drive is not mounted inside the system unit. Due to the additional distance, data cannot reliably be transferred at high speed over copper cable. The transfer rate of an external hard drive is slower than an internal hard drive of the otherwise identical design.
A removable hard disk is a hard disk that can be removed from its disk drive. The disk drive can be either an internal or external hard drive.
4a. How is a single-session disk different from a multisession disk?
A single session CD ROM must have all data written onto the CD at the same time. Additions cannot be made at a later time.
From DiscUSA: A multisession CD comprises more than one session, each of which comprises Lead-in, Program area and Lead-out and (for a recordable CD) can be written at different times (ie sessions). Multisession CD specification for pressed disks is a Philips/Sony standard (actually yellow in color) defining disks which have two or more sessions but are pressed not recordable. The only pressed multisession disk format currently defined is the Enhanced Music CD, defined in the Blue Book.
Session: An area of a multisession CD consisting of a Lead-In area, Program area and a Lead-Out area. On a CD-R it allows the data to be written a session at a time. Up to 99 sessions may be written to a single disc.
A great tutorial on the world of CDs is at http://www.discusa.com/technology/cdbasics/cd_intro.htm
4b. What is a multiread CD drive?
A multiread CD drive is one that reads audio CDs, data CDs, CD-Rs, and CD-RWs.
5a. How is sequential access different from direct access?
Sequential access means that data is stored in a linear sequence, such as on tape. If your present position in a file is at the beginning of record 10, and you want to read record 13 next, you must read or skip over records 10, 11, and 12 to get to record 13. Some sequential access storage devices, such as main frame tape drives, permit reading sequential medium backwards as well as forwards. If your present position is at the beginning of record 16 and you want to read record 13, you have to backspace or read backwards through records 15 and 14 to get to the end of record 13. Less sophisticated tape drives require you to rewind and read from the beginning of the tape to get to the beginning of record 13. Sequential media are not routinely used for applications requiring random access of records. Much of the processing in a transaction processing system is efficiently done using sequential access media.
Direct access, also called random access, means that the device can locate a particular data item or file immediately without having to move consecutively through items stored in front of the desired data item or file. Primary memory of a computer is an example of random access storage. Disks are called direct access devices, and access is almost direct. The drive arm positions directly to the required track, but the proper sector is searched for sequentially. Another device that is called random access that shares this hybrid property is magnetic bubble memory.
By the way, even disks can be used as sequential access devices even though they are capable of being used in direct access mode.
5b. When reading or writing specific data stored at a
specific physical location, which type of access is faster?
Direct access is almost always faster than sequential access if the initial position in the file is not known to be just before the desired position. Given a sequential file and a random access file on the same disk, the random access file may have additional table look-up overhead to determine the location of the desired record, while the sequential file will not have that overhead. If the write arm is positioned at the proper track, and the desired record is ahead of the current record pointer when the read request is received, the random access file may require the arm to reposition to the track containing a look-up table, and then reposition back to the proper track, finally to read the record. The sequential access file strategy only requires for the proper record to rotate under the read head. In this case, the sequential access organized file record is retrieved faster than the direct access file record. The intended application has much to do with selection of the proper storage format.
3. a. What is a head crash?
Answer: A head crash on a hard disk is the unintentional contact of the read/write head with the disk on a data area. Normally, the read/write head literally flies above the hard disk surface while the disk is in motion. The head is shaped as an airfoil, and floats using wing-in-ground effect.
Intentional contact of the read/write head with the hard disk surface can occur in a specified landing zone when the disk is slowing down after being turned off. The landing zone is not a data recording area. This is not considered a head crash. On main frame hard drives, the heads retract. On some laptop computers, you must park the head before you turn your computer off. Newer laptops do this automatically.
Because the head is supposed to make physical contact with the surface of a floppy disk, you cannot have a head crash on a floppy disk.
3. b. How does a disk cache improve hard disk access time?
Answer: A disk cache is a storage area used to store information retrieved from disk in advance of a request. Disk cache does not speed up the transfer of data. The disk cache is used to make the comparatively slow hard disk more responsive to the much faster CPU. Smart operating systems will often read several records beyond the last requested record, anticipating that the program initiating the previous request will want the next record in sequence. If the gambit is successful, then the data will already be in memory (the cache) when it is requested. On main frame computers, the details of data storage and retrieval are handled by an input/output control system rather than completely by the operating system. Handling the details of a disk cache in this way further improves the computer system by not burdening the CPU unnecessarily.
4.a. How does an Internet hard drive work?
Answer: An Internet hard drive is a storage service provided on a server attached to the Internet. You may save files from a local or a remote computer to an Internet hard drive.
4.b. Why would someone want to use one of these?
Answer:
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Use of an Internet hard drive gives you the freedom of accessing a file from any computer that has access to the Internet. This is useful for the traveler or for sharing files with other people. |
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Use of an Internet hard drive reduces the storage demand on a local drive. |
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An Internet hard drive provides an off-site backup capability for critical files. |
4.c. What disadvantages could there be?
Answer:
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Storage space costs money. Someone has to pay. Even a "free" service subsidized by advertisements can result in unexpected charges if you exceed a capacity limit. |
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Internet servers are sometimes not available during bad weather or periods of high traffic on the Internet. |
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Unless stored data is encrypted, it is available to unscrupulous system administrators, and possibly to others. If you do not want something to be public knowledge, do not let it go over the Internet. |
5. b. What are the four basic formats of compact disks?
Answer: Four basic formats of compact disks are the CD-ROM, the recordable CD (CD-R), and the rewriteable CD (CD-RW), and the digital video disk (DVD).
5.c. How are CD-Rs and CD-RWs different?
Answer: All CDs are recorded and read by using a laser.
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The CD is recorded by burning microscopic pits into the recording surface. |
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A CD-R writes data to a disc by using it's laser to physically burn pits into the organic dye. When heated beyond a critical temperature, the area ‘burned’ becomes opaque and reflects less light than areas that have not been heated by the laser. |
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CD-RW commonly uses a crystalline compound. When it’s heated to one temperature and cooled it becomes crystalline, but if it’s heated to a higher temperature, when it cools down again it becomes amorphous. The crystalline areas allow the metalised layer to reflect the laser better while the non-crystalline portion absorbs the laser beam, so it is not reflected. 'Direct overwriting' and the process can be repeated several thousand times per disk. |
4. a. What is a disk controller?
A disk controller is a device that controls the positioning of the read/write arm, regulates the speed of the disk, and measures the rotational position of the disk. It may also manage data transfer between the disk and a disk cache built into the controller. The controller transmits the data to the computer according to the bus standards for which the controller was designed.
4. b. How are EIDE controllers and SCSI controllers different?
These controllers differ in transmission rate and the number of devices the controller can handle. SCSI is at least 3 times faster than EIDE, and SCSI can handle at least 3 times as many devices as EIDE.
Mitchell Shnier, Dictionary of PC Hardware and Data Communications Terms, O'Reilly http://www.ora.com/reference/dictionary/
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IDE, Integrated Drive Electronics: 1-2 hard disks, 504 MB capacity, 1-3 MB/s. |
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E-IDE, Enhanced Integrated Drive Electronics, 1-4 hard disks per adapter, 8.033 GB capacity, 16.6 MB/s. http://www.ora.com/reference/dictionary/terms/E/Enhanced_IDE.htm |
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ATA-5 (1999): 66.6 MB/s maximum. |
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SCSI, Small Computer System Interface: 7 devices daisy chained, 100 MB/s. |
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Ultra3 SCSI can support up to 16 devices on a 16-bit bus and transfer data at 160 MB/s. |
For more information, visit the SCSI Trade Association at http://www.scsita.org/ .
