Which of the following types of storage devices makes it possible to store and retrieve data at a later stage?
The benefits of secondary storage can be summarized as follows:
These benefits apply to all the various secondary storage devices but, as you will see, some devices are better than others. We begin with a look at the various storage media, including those used for personal computers, and then consider what it takes to get data organized and processed. Diskettes and hard disks are magnetic media; that is, they are based on a technology of representing data as magnetized spots on the disk with a magnetized spot representing a 1 bit and the absence of such a spot representing a 0 bit. Show Diskettes Made of flexible Mylar, a diskette can record data as magnetized spots on tracks on its surface. Diskettes became popular along with the personal computer.
For more details on floppy disks and drives click here. This is optional reading .
A disk drive is a machine that allows data to be read from a disk or written on a disk. A disk pack is mounted on a disk drive that is a separate unit connected to the computer. Large computers have dozens or ever hundreds of disk drives. In a disk pack all disks rotate at the same time although only one disk is being read or written on at any one time. The mechanism for reading or writing data on a disk is an access arm; it moves a read/write head into position over a particular track. The read/write head on the end of the access arm hovers just above the track but does not actually touch the surface. When a read/write head does accidentally touch the disk surface, this is called a head crash and all data is destroyed. Data can also be destroyed if a read/write head encounters even minuscule foreign matter on the disk surface. A disk pack has a series of access arms that slip in between the disks in the pack. Two read/write heads are on each arm, one facing up for the surface above it and one facing down for the surface below it. However, only one read/write head can operate at any one time. In some disk drives the access arms can be retracted; then the disk pack can be removed from the drive. Most disk packs, however, combine the disks, access arms, and read/write heads in a sealed module called a Winchester disk. Winchester disk assemblies are put together in clean rooms so even microscopic dust particles do not get on the disk surface. Hard disks for personal computers are 5-1/4 inch or 3-1/2 inch disks in sealed modules and even gigabytes are not unusual. Hard disk capacity for personal computers has soared in recent years; capacities of hundreds of megabytes are common and gigabytes are not unusual. Although an individual probably cannot imagine generating enough output-letters, budgets, reports, and so forth-to fill a hard disk, software packages take up a lot of space and can make a dent rather quickly. Furthermore, graphics images and audio and video files require large file capacities. Perhaps more important than capacity, however, is the convenience of speed. Personal computer users find accessing files on a hard disk is significantly faster and thus more convenient than accessing files on a diskette. For more details on hard disks and drives found in modern PCs, click here. This is optional reading .
The most popular removable disk media is the Zip drive from Iomega (Figure 3). Over 100's of millions have been sold, making it the de facto standard. The disk cartridges look like a floppy disk, but are slightly bigger in all dimensions. Older Zip disks hold 100MB, newer ones hold 250MB and cost $8-$10 a piece (Floppies hold 1.4MB and cost around $2). The drive sells for around $80- $125. Many new PCs come with Zip drives built in addition to floppy drives. Zip disks are a great way to store large files and software programs. For more details on removable storage such as Zip drives, click here . This is optional reading .
The explosive growth in storage needs has driven the computer industry to provide cheaper, more compact, and more versatile storage devices with greater capacity. This demanding shopping list is a description of the optical disk, like a CD. The technology works like this: A laser hits a layer of metallic material spread over the surface of a disk. When data is being entered, heat from the laser produces tiny spots on the disk surface. To read the data, the laser scans the disk, and a lens picks up different light reflections from the various spots. Optical storage technology is categorized according to its read/write capability. Read-only media are recorded on by the manufacturer and can be read from but not written to by the user. Such a disk cannot, obviously, be used for your files, but manufacturers can use it to supply software. Applications software packages sometimes include a dozen diskettes or more; all these could fit on one optical disk with plenty of room to spare. The most prominent optical technology is the CD-ROM, for compact disk read-only memory. The disk in its drive is shown in Figure 3.
When buying a computer the speed of the CD-ROM drive is advertised using an "X" factor, like 12X, or 24X. This indicates the speed at which the CD can transfer data to the CPU - the higher the X factor, the faster the CD. Modern computers now offer a write CD drive or, CD-RW as an option. CD-RW is a write-once, read-many media. With a CD-RW drive, you can create your own CDs. This offers an inexpensive, convenient, safe way to store large volumes of data such as favorite songs, photographs, etc. For more details on CD
technology, click here. This is optional reading .
A 4.7 GB side of a DVD can hold 135 minutes top quality video with 6 track stereo. This requires a transmission rate of 4692 bits per second. The 17 GB disk holds 200 hours top quality music recording. DVD movies are made in two "codes." Region one is USA and Canada, while Europe and Asia is region two. When you play movies, your hardware (MPEG decoder. MGEG is the data coding for movies similar to JPEG for pictures.) must match the DVD region. The movies are made in two formats, each with their own coding. The DVD drives come in 2X, 4X, etc. versions, like the CD-ROM's. The DVD drives will not replace the magnetic hard disks. The hard disks are being improved as rapidly as DVD, and they definitely offer the fastest seek time and transmission rate (currently 5-10 MB/second). No optic media can keep up with this. But the DVD will undoubtedly gain a place as the successor to the CD ROM and is playing an important role in the blending of computers and entertainment centers. For more detail on DVD technology, click here . This is optional reading . We saved magnetic tape storage for last because it has taken a subordinate role in storage technology. Magnetic tape looks like the tape used in music cassettes plastic tape with a magnetic coating. As in other magnetic media, data is stored as extremely small magnetic spots. Tapes come in a number of forms, including l/2-inch-wide tape wound on a reel, l/4-inch- wide tape in data cartridges and cassettes, and tapes that look like ordinary music cassettes but are designed to store data instead of music. The amount of data on a tape is expressed in terms of density, which is the number of characters per inch (cpi) or bytes per inch (bpi) that can be stored on the tape. The highest-capacity tape is the digital audio tape, or DAT, which uses a different method of recording data. Using a method called helical scan recording, DAT wraps around a rotating read/write head that spins vertically as it moves. This places the data in diagonal bands that run across the tape rather than down its length. This method produces high density and faster access to data. Two reels are used, a supply reel and a take-up reel. The supply reel, which has the tape with data on it or on which data will be recorded, is the reel that is changed. The take-up reel always stays with the magnetic tape unit. Many cartridges and cassettes have the supply and take-up reels built into the same case. Tape now has a limited role because disk has proved the superior storage medium. Disk data is quite reliable, especially within a sealed module. Furthermore, as we will see, disk data can be accessed directly, as opposed to data on tape, which can be accessed only by passing by all the data ahead of it on the tape. Consequently, the primary role of tape today is as an inexpensive backup medium. Although a hard disk is an extremely reliable device, a hard disk drive is subject to electromechanical failures that cause loss of data. Furthermore, data files, particularly those accessed by several users, are subject to errors introduced by users. There is also the possibility of errors introduced by software. With any method of data storage, a backup system a way of storing data in more than one place to protect it from damage and errors is vital. As we have already noted, magnetic tape is used primarily for backup purposes. For personal computer users, an easy and inexpensive way to back up a hard disk file is to simply copy it to a diskette whenever it is updated. But this is not practical for a system with many files or many users. Personal computer users have the option of purchasing their own tape backup system, to be used on a regular basis for copying all data from hard disk to a high-capacity tape. Data thus saved can be restored to the hard disk later if needed. A key advantage of a tape backup system is that it can copy the entire hard disk in minutes, saving you the trouble of swapping diskettes in and out of the machine. A rule of thumb among computer professionals is to estimate disk needs generously and then double that amount. But estimating future needs is rarely easy. Many users, therefore, make later adjustments like adding a removable hard disk cartridge to accommodate expanding storage needs. To quote many a computer user, "I just couldn't envision how I could use all that disk space. Now I can imagine even the extra disk filling up." What device can store and retrieving data?Hard drives, or disks, are a very common storage device for personal computers. There are internal and external hard drives, but both use a magnetic disk to function. Magnetic disks are what store the data that will later be processed to run programs or open files.
What is primary and secondary storage?Primary memory usually refers to Random Access Memory (RAM), while secondary storage refers to devices such as hard disk drives, solid state drives, removable “USB” drives, CDs, and DVDs.
Which storage device is used to store the data permanently?Permanent storage, also called persistent storage, is any computer data storage device that retains its data when the device is unpowered. A common example of permanent storage is the computer's hard drive or SSD.
Which type of devices are used to store data?External storage devices. External HDDs and SSDs. ... . Flash memory devices. ... . Optical Storage Devices. ... . Floppy Disks. ... . Primary Storage: Random Access Memory (RAM) ... . Secondary Storage: Hard Disk Drives (HDD) & Solid-State Drives (SSD) ... . Hard Disk Drives (HDD) ... . Solid-State Drives (SSD). |