Computer Science
Magnetic Storage
Magnetic storage refers to the technology of storing data using magnetized materials, such as hard disk drives and magnetic tapes. In this method, data is encoded as magnetic patterns on the storage medium, allowing for non-volatile and relatively high-capacity storage. Magnetic storage has been a fundamental component of computer systems for decades, providing a cost-effective and reliable means of data storage.
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10 Key excerpts on "Magnetic Storage"
- Bane Vasic, Erozan M. Kurtas, Bane Vasic, Erozan M. Kurtas(Authors)
- 2004(Publication Date)
- CRC Press(Publisher)
1 A Brief History of Magnetic Storage Dean Palmer Seagate Technology Minneapolis, MN 1.1 Introduction .......................................... 1 -1 1.2 The Early Days of Magnetic Recording ................. 1 -1 1.3 Tape Drives ........................................... 1 -5 1.4 Disk Drives ........................................... 1 -9 1.5 Acknowledgements ................................... 1 -15 1.1 Introduction With the advent of the digital computer in the 1950s, there arose a parallel, seemingly insatiable need for digital storage and memory. Early computer architects turned to existing forms of storage such as punched Hollerith cards derived from loom machinery and magnetic recording developed by the audio recording industry. Other forms were quickly devised: paper tape, magnetic core, then semiconductor memory and optical recording. These technologies evolved into the current hierarchy of computer storage: fast semiconductor memory in and attached to the processor, magnetic disks providing quick access to volumes of data, optical and magnetic disks as input/output devices, and magnetic tape for back-up and archival purposes. But in terms of sheer volume of data stored and manipulated on a continuous basis, it is the magnetic media that provide the foundation of this storage pyramid. Data stored on magnetic recording devices are found everywhere. We carry magnetic data on our credit cards and transportation tickets, we use magnetic recording devices to store our computer programs, e-mails, Internet transactions, and personal photos, and we find more and more of our entertainment in a variety of magnetic recording formats. Having recently celebrated its 100th anniversary, magnetic recording could be considered a very mature technology, except for the rapid pace of innovation that continues today. And the trends in Magnetic Storage continue to be toward smaller, faster, cheaper and denser devices, with no sure end in sight.
eBook - PDF- T. F. Fry(Author)
- 2014(Publication Date)
- Newnes(Publisher)
First of all, to review briefly the different kinds of backing store commonly used in computers. These are: Magnetic tapes; Magnetic drums; Magnetic discs; Magnetic cards; Magnetic strips; Magnetic stripes. The nature of the physical construction of these types of store will determine how individual items of data can be located. To find an item 72 Computer Storage 73 stored on magnetic tape it is necessary to run the tape over a reading head until the item sought is located. Magnetic drums and discs have the whole recording surface accessible at any one time providing a means of going direct to any specific item of data, while magnetic cards and strips can be individually selected from a magazine at will and so provide a means of directly accessing the data recorded on them. In the storage media listed above, magnetic tape is known as serial access storage, while the other four are, to a greater or lesser degree, direct access storage. MAGNETIC TAPE L Physical characteristics Most magnetic tape used in computer storage is Vi in wide and made of a tough plastic such as Mylar. It is coated with a material that can be permanently magnetised and is held on spools of varying lengths, up to 2400 ft. Tape is processed on an 'on-line' peripheral device known as a tape transport. Depending on central processor hardware, a number of transports can be linked to the processor at the same time. On the transport, the tape is fed from a feed reel to a take-up reel over read and write heads; some transports have an additional erase head, although in many cases the write head serves a dual purpose; to write and erase. 2. Mode of recording Individual characters are recorded as a line of small areas or dots across the width of the tape representing binary bits, magnetised in the opposite direction to the permanent field on the tape. The positioning of bits longitudinally on the tape are on what are known as 'tracks'.
eBook - ePubFoundations of Computing
Essential for Computing Studies, Profession And Entrance Examinations - 5th Edition
- Pradeep K. Sinha, Priti Sinha(Authors)
- 2022(Publication Date)
- BPB Publications(Publisher)
Direct-access devices are useful for such applications, which need to access information in a more direct manner than sequential-access devices allow. For example, in a computerized bank, at any instance, we may require to determine the exact balance in a customer's savings account. Similarly, in a computerized airline ticket booking system, we may require immediate access to reservation system records to find out, if seats are available on a particular flight. In such applications, if we use a sequential-access device for data storage, accessing desired information may take a long time, causing frustration to the customer.Magnetic disks, optical disks, solid state drive and memory storage devices are examples of direct-access storage devices.MAGNETIC TAPES
Magnetic tape is the most popular storage medium for large data sets accessed and processed sequentially. Computer systems also use it as a backup storage for data stored on on-line storage devices such as a hard disk.Magnetic tape medium is a plastic ribbon usually ½-inch or ¼-inch wide and 50 to 2400 feet long. Its surface has a coating (such as iron oxide or chromium dioxide) that can record data by magnetization. Data is recorded on the coated surface as tiny, invisible magnetized and non-magnetized spots (representing 1s and 0s). Tape ribbon itself is stored in reels, or a small cartridge, or cassette.We can erase old data and record new data on magnetic tapes. As we record new data on it, it erases old data in the same area. However, we can read stored data many times without affecting it.Basic Principles of Operation
Storage Organization
A tape consists of vertical columns called frames , and horizontal rows called channels or tracks . Most modern magnetic tapes have 9 tracks, and use 8-bit EBCDIC code format for data recording (see Figure 5.2 ). The fourth track records parity bit. A parity bit or check bit enables detection of errors that may occur due to loss of a bit from a string of 8 bits during data input or output operations. In odd-parity, the check bit is 0, if the total number of 1 bits for representing a character is odd and it is 1, otherwise. On the other hand, in even parity , the check bit is 0 if the total number of 1 bits for representing a character is even and it is 0, otherwise. The tape in Figure 5.2
eBook - PDF- Stephen D. Burd(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
As fabrication techniques improve, the amount of memory that can be pack-aged with the CPU on a single chip grows. The logical extension of this trend is placing a CPU and all its primary storage on a single chip, which would minimize or eliminate the current gap between microprocessor clock rates and memory access speeds. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 5 162 Magnetic Storage Magnetic Storage devices exploit the duality of magnetism and electricity. That is, electri-cal current can generate a magnetic field, and a magnetic field can generate electricity. A Magnetic Storage device converts electrical signals into magnetic charges, captures the magnetic charge on a storage medium, and later regenerates an electrical current from the stored magnetic charge. The magnetic charge’s polarity represents the bit values 0 and 1. Figure 5.6 illustrates a simple Magnetic Storage device. A wire is coiled around a metallic read/write head . To perform a write operation, an electrical current is passed through the wire, which generates a magnetic field across the gap in the read/write head. The direction of current flow through the wire determines the field’s polarity—that is, the position of the positive and negative poles of the magnetic field. Reversing the current’s direction reverses the polarity. A Magnetic Storage medium is placed next to the gap. The storage medium is coated with a metallic compound with high coercivity —the capability to accept and hold a mag-netic charge.
eBook - PDFComputer Organisation and Architecture
An Introduction
- B.S. Chalk, Antony Carter, Robert Hind(Authors)
- 2017(Publication Date)
- Red Globe Press(Publisher)
Secondary memory In Chapter 6 we looked at the RAM, Random Access Memory, that is very closely attached to the processor chip. The big problem with this memory is that when the power is switched off, the stored data is lost. In every computer system, it is necessary to be able to store data and programs even when the power to the computer system is turned off. The devices that provide this facility are called secondary memory or backing storage and this chapter looks at a number of these devices. The two main technologies used for secondary storage devices are magnetic surface and optical technology. 7.1 Magnetic surface technology Dynamic Magnetic Storage systems record data by inducing tiny magnetized spots called dipoles on to a moving magnetic surface. To read or write data, the surface is moved past a read/write head, as shown in Figure 7.1(a). Data is 109 C H A P T E R 7 Figure 7.1 Magnetic surface recording read–write head coil sense amplifier vertical recording and driver motion (a) (b) 0 1 substrate dipole surface flux induced voltage written on to the surface by driving a current through the head coil windings. The direction of the current determines the orientation of the dipole and hence whether a binary ‘1’ or ‘0’ is stored. With horizontal recording , the dipoles lie along the direction of motion of the surface, whilst with vertical recording , they are oriented in a perpendicular direction. During a read operation, the surface magnetic field generated by a dipole Figure 7.1(b) induces a voltage signal across the coil, the polarity being dependent upon the direction of the magnetic field. After passing through the sense amplifier, the signal is fed into an electronic circuit where it is processed and the encoded data extracted. 7.2 Magnetic disk storage 7.2.1 Hard disks A widely used form of secondary storage is the hard disk , shown in Figure 7.2(a).
eBook - PDFData Storage at the Nanoscale
Advances and Applications
- Gan Fuxi, Wang Yang, Gan Fuxi, Wang Yang(Authors)
- 2015(Publication Date)
- Jenny Stanford Publishing(Publisher)
Although they have been partly replaced by the flash memory nowadays, the HDD is still one of the most common storage devices, especially for the vast capacity situation. The HDD is the main device for magnetic recording, usually used in our computers and data centers. More and more people are using electronic copies instead of papers. With the increasing development of network, backing up data on the Internet has become a reality. Large amounts of data in various applications with mass amount of information can be stored somewhere in data centers, which need a huge number of HDDs. Magnetic recording is non-volatile; because of this, digital information is stored in a stable manner with two distinctive states of magnetization at a localized site. The two states can be read by a magnetic sensor (read head) and altered by an inducer driven by a current (write head). The fundamental concept of magnetic recording in HDD uses an inductive magnetic head, which normally consists of coils wound around a magnetic soft pole, to write down the information on the medium (magnetically hard material). Figure 14.1 illustrates the fundamental principle of magnetic recording in the case of magnetization along the film plane. The inset enlarges a transition area between two opposite magnetizations with some magnetic grains. During the write process, a current passes through the coils, generating a magnetic field above the magnetic medium. We can change the write current directions and consequently reverse the magnetization directions of the bits on the medium, which represents “1” and “0” states. The data is read by measuring the stray magnetic field from the transitions. Finally, a signal-processing unit transforms the analog read-back signal into a stream of data bits.
eBook - PDFScientific Data Management
Challenges, Technology, and Deployment
- Arie Shoshani, Doron Rotem, Arie Shoshani, Doron Rotem(Authors)
- 2009(Publication Date)
- Chapman and Hall/CRC(Publisher)
This chapter will focus on the characteristics of the fundamental building blocks used to construct parallel file systems to meet the needs of scientific applications at scale. Understanding the unprecedented requirements of these new computing paradigms, in the context of high-end HPC I/O subsystems, is a key step toward making effective petascale computing a reality. The main contribution of this chapter is to quantify these tradeoffs in cost, performance, reliabil-ity, power, and density of storage systems by examining the characteristics of the underlying building blocks for high-end I/O technology. This chapter projects the evolution of the technology as constrained by historical trends to Storage Technology 5 understand the effectiveness of various implementations with respect to abso-lute performance and scalability across a broad range of key scientific domains. 1.2 Fundamentals of Magnetic Storage Magnetic recording technology was first demonstrated in 1898. Magnetic stor-age has been closely associated with digital computing since the dawn of the industry. Its performance and cost-effectiveness ensure that it will continue to play an important role in nonvolatile storage for some time to come. The primary factor that consistently drives down the cost of storage media is the ability to double storage density consistently on an annual basis as shown in the storage trends in Figure 1.3. As we reach physical limits of the media, the storage density trends can no longer continue and the market may change dramatically. Until then, Magnetic Storage will continue to play a leading role in nonvolatile storage technology. This section elucidates the physics underly-ing the Magnetic Storage technology and the current challenges to improving storage density. The underlying media for magnetic recording are ferromagnetic materi-als.
Available until 4 Dec |Learn moreInformation Systems
What Every Business Student Needs to Know
- Efrem G. Mallach(Author)
- 2015(Publication Date)
- Chapman and Hall/CRC(Publisher)
They are the least expensive type of storage that is fast enough to serve as a computer’s only secondary storage. Other technologies are either too slow or more expensive. Magnetic disks use platters of aluminum or glass coated with a magnetizable cobalt-based alloy. An electromagnet called a read/write head magnetizes a spot on Information Systems Hardware ◾ 79 the surface in one direction or the other to record a bit as 0 or 1. To write data, the device goes through these steps: 1. It moves the head over the disk surface to the correct circular track . The head is at the upper right end of the arm in Figure 3.10. It is moved by a positioning motor at the other end of the arm. The arm rotates about a pivot to move the head in and out over the recording surfaces. 2. It waits until the appropriate section of the track, or sector , rotates under the head. 3. It sends electromagnetic pulses to set the magnetization of the bits in that sector. The first two steps are the same when a disk reads data. Step 3 is different: the head detects the magnetic field that is generated as it passes over the surface and interprets that field as a 0 or a 1. Most magnetic disk drives are installed permanently in their enclosures, inside the main computer structure ( internal drives ) or attached to it by a cable ( external drives ). This protects them from airborne contaminants. High-capacity drives require very close toler-ances. Even a small dust particle can destroy them if it comes between the head and the recording surface. Most external drives need to be connected to a power supply as well as to a computer. External drives that are powered through their computer connections are called portable drives . FIGURE 3.10 Magnetic disk. (From public domain illustration from www.clipartsfree.net/ clipart/772-open-disk-drive-clipart.html.) 80 ◾ Information Systems: What Every Business Student Needs to Know Removable magnetic disks were used in the past but are seldom seen today.
- Misty Vermaat, Susan Sebok, Steven Freund, Jennifer Campbell(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 8-8 Module 8 Digital Storage The storage capacity of hard disks varies and is determined by the number of platters the hard disk contains, the composition of the magnetic coating on the platters, whether it uses longitudinal or perpendicular recording, and its density. • A platter is made of aluminum, glass, or ceramic and has a thin coating of alloy material that allows items to be recorded magnetically on its surface. • Longitudinal recording aligns the magnetic particles horizontally around the surface of the disk. With perpendicular recording , by contrast, hard disks align the magnetic particles vertically, or perpendicular to the disk’s surface, making much greater storage capacities possible. • Density is the number of bits in an area on a storage medium. A higher density means more storage capacity. Hard disks are read/write storage media. That is, you can read from and write on a hard disk any number of times. Before any data can be read from or written on a hard disk, however, the disk must be formatted. Formatting is the process of dividing the disk into tracks and sectors (Figure 8-5) so that the operating system can store and locate data and information on the disk. A track is a narrow recording band that forms a full circle on the surface of the disk. The disk’s storage locations consist of wedge-shaped sections, which break the tracks into small arcs called sectors . On a hard disk, a sector typically stores up to 512 bytes of data. Sometimes, a sector has a flaw and cannot store data.
eBook - PDF- Aharon Yadin(Author)
- 2016(Publication Date)
- Chapman and Hall/CRC(Publisher)
This type of media was heavily used in the past, mainly for backup purposes, but in recent years, its usage has been limited. The major limitation of such devices is that the search time is influenced by the location of the searched item. • Random (or direct) access, in which it is possible to get to the required item directly. Memory, for example, is a direct-access device. The access time for obtaining a data item using direct access is almost similar for all items, regardless of their location. 312 ◾ Computer Systems Architecture Another classification for storage devices is their online level: • Fully online, which means that the device is always online and all its data is con-stantly available. Most magnetic disks installed in a computer system are fully online. • Partially online, which usually involves a robotic system that holds a library of disks (e.g., optical disks); when a disk is required, it will issue the commands to stage it. This type of device provides limitless storage; however, the first access may require time, and sometimes even a significant amount of time (in cases where all the disk readers are occupied). As technology advances and online storage prices decrease, especially for the various cloud-based solutions that are being proposed, the usage and wide spread of partially online storage is decreasing. • Off-line, which means the device is not connected to the system and its data is not available. The most trivial example may be the disk-on-key, which holds the data off-line, and when the need arises, the disk is connected to the system and its content becomes available. There are organizations that, for security reasons, use the same method but with removable hard drives. In both cases, these are off-line devices. Disk Structure Most magnetic disks share a very similar structure ( Figure 9.2 ): • The disk comprises one or more round platters on an axle, each one covered with a magnetic material.
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