Secondary Storage

10 Key excerpts on "Secondary Storage"

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  eBook - ePub

  Computer Fundamentals - 8th Edition

  Concepts, Systems & Applications

  • Pradeep K.Sinha, Pradeep K.Sinha, Priti Sinha(Authors)
  • 2004(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 8

  Secondary Storage Devices

  Primary storage of today's computer systems has following limitations:

  1. Limited capacity. It is often necessary to store many millions, sometimes billions, and even trillions, of bytes of data in a computer. Unfortunately, storage capacity of primary storage of today's computers is not sufficient to store the large volume of data handled by most users.
  2. Volatile. Primary storage is volatile and it loses data stored in it in case of power off or interruption of power. However, computer systems need to store data on permanent basis for several days, several months, or even several years.

  To overcome the limitations of primary storage, almost all computers use additional memory called auxiliary memory or Secondary Storage . Secondary Storage is non-volatile and has lower cost per bit stored, but operates generally at speeds far slower than that of primary storage. Computer systems use it primarily to store large volume of data on permanent basis, which they transfer partially to primary storage, whenever required for processing.

  Over the years, computer systems have used several devices and media as Secondary Storage. Many of them such as punched paper tape, punched cards, and floppy disks have become obsolete now. Figure 8.1 shows the popular ones used in today's computer systems. In this chapter, you will learn about the terminologies, principles of operation, uses, and trade-offs of different types of Secondary Storage devices.

  Figure 8.1. Commonly used Secondary Storage devices and their classification.

  SEQUENTIAL AND DIRECT-ACCESS DEVICES

  Although there are several different devices that one can use as a Secondary Storage device, the one selected for a particular application depends mainly upon how the application needs to access the stored information. There are two methods of accessing information - sequential or serial access, and direct or random access.

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  eBook - PDF

  Silberschatz's Operating System Concepts

  • Abraham Silberschatz, Peter B. Galvin, Greg Gagne(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  Part Five Storage Management Computer systems must provide mass storage for permanently storing files and data. Modern computers implement mass storage as Secondary Storage, using both hard disks and nonvolatile memory devices. Secondary Storage devices vary in many aspects. Some transfer a character at a time, and some a block of characters. Some can be accessed only sequentially, and others randomly. Some transfer data syn- chronously, and others asynchronously. Some are dedicated, and some shared. They can be read-only or read – write. And although they vary greatly in speed, they are in many ways the slowest major component of the computer. Because of all this device variation, the operating system needs to provide a wide range of functionality so that applications can control all aspects of the devices. One key goal of an operating system’s I/O subsystem is to provide the simplest interface possible to the rest of the system. Because devices are a performance bottleneck, another key is to optimize I/O for maximum concurrency. 11 C H A P T E R Mass-Storage Structure In this chapter, we discuss how mass storage — the nonvolatile storage sys- tem of a computer—is structured. The main mass-storage system in modern computers is Secondary Storage, which is usually provided by hard disk drives (HDD) and nonvolatile memory (NVM) devices. Some systems also have slower, larger, tertiary storage, generally consisting of magnetic tape, optical disks, or even cloud storage. Because the most common and important storage devices in modern com- puter systems are HDDs and NVM devices, the bulk of this chapter is devoted to discussing these two types of storage. We first describe their physical struc- ture. We then consider scheduling algorithms, which schedule the order of I/Os to maximize performance. Next, we discuss device formatting and manage- ment of boot blocks, damaged blocks, and swap space.

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  eBook - PDF

  Guide to Operating Systems

  • Palmer, Greg Tomsho(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Dozens of cloud storage services are competing to store your files, and although these services are convenient and seemingly work by magic, they all start with a computer and some hard drives. The following sections cover some basics of computer storage: what it is, why you need it, and the common methods for accessing storage. What Is Storage? Generally speaking, storage is any digital medium that data can be written to and later retrieved. Technically, this definition includes random access memory (RAM), but the term computer storage generally means long-term storage in which data is maintained without a power source. For example, RAM only holds data when it has electrical power — this is referred to as volatile storage . Long-term storage maintains data when the power is turned off, and is referred to as nonvolatile storage . Long-term storage includes the following types of media: • USB memory sticks (flash drives) • Secure Digital (SD) cards and Compact Flash (CF) cards • CDs and DVDs • Magnetic tape • Solid-state drives • Hard disk drives This discussion centers on internal computer storage, which is based on hard disk drives (HDDs), although solid-state drives (SSDs) are rapidly closing the price and performance gap with HDDs. SSDs are very popular for applications requiring greater speed, smaller size, and lower power requirements. An SSD uses flash memory and the same type of high-speed interfaces (usually SATA or the newer SATA Express) as traditional hard disks. An SSD has no moving parts, requires less power, and is faster and more resistant to shock than an 314 Chapter 7 Using and Configuring Storage Devices Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 HDD, but the cost is higher per gigabyte than an HDD. Also, SSDs don ’ t yet have the capacity of HDDs, so discussions of computer storage are mainly about traditional HDD storage.

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  eBook - ePub

  Foundations of Computing

  Essential for Computing Studies, Profession And Entrance Examinations - 5th Edition

  • Pradeep K. Sinha, Priti Sinha(Authors)
  • 2022(Publication Date)
  • BPB Publications

    (Publisher)

  HSM ) software automatically handles this. Hence, all HSSs have HSM software, which monitors the way data is used, and makes decisions as to which data can be moved safely to slower devices (near-line storage) and which data should stay on fast devices (on-line storage). In a typical scenario, HSM stores frequently used data on on-line storage, but eventually moves them to near-line storage, if the system does not access them for a certain period, typically a few months. If the system accesses a data on near-line storage, HSM moves it back automatically from near-line storage to on-line storage. The advantage is that since only rarely used data is on near-line storage, most users do not notice any slowdown in data access. Moreover, users do not need to know or keep track of where the accessed data is stored and how to get it back.

  The computer retrieves the data automatically. Notice that movement of data to/from off-line storage still requires human intervention because a human operator has to insert or connect an off-line media or device to the computer system for initiating data transfer.

  Points to Remember

  1. Primary storage of a computer system has limited capacity and is volatile. Hence, most computer systems use additional memory, called auxiliary memory or Secondary Storage .
  2. Secondary Storage of a computer system is non-volatile and has low cost per bit stored, but operates at speeds far slower than that of primary storage.
  3. A sequential-access storage device is one in which the arrival at a desired location is preceded by sequencing through other locations so that access time varies according to location. On the other hand, a random-access storage device is one in which we can reach and access any storage location at random, and approximately equal access time is required for accessing each location.
  4. Magnetic tape

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  eBook - PDF

  Computer 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).

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  Available until 4 Dec |Learn more

  Information Systems

  What Every Business Student Needs to Know

  • Efrem G. Mallach(Author)
  • 2015(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  If an office worker’s desk is too small, the worker can pile papers on top of each other, shuffling piles around to reach what is needed at any time. Computers can do the same, moving data temporarily to Secondary Storage (see the next section) to free up RAM for other data. This is called paging . Using paging, a computer with 2 GB RAM can behave as if it had 4 GB or even more. However, there are limits to how much virtual memory can be added this way. If a computer with 2 GB RAM tries to act as if it had 16 GB, the delays of moving data between RAM and Secondary Storage will be unacceptable. It will per-form slowly or not at all—like the office worker in Figure 3.8, who has to spend so much time rearranging papers that he can’t do much useful work. This effect is called thrashing . Thrashing is a sign that you need more RAM. Secondary Storage Secondary Storage provides long-term storage for data that may be needed minutes, months, or years later. A Secondary Storage device should combine high storage capacity, speedy access, low cost, and long-term reliability. No device is ideal in all these respects. Secondary Storage technologies offer different trade-offs among these factors. The choice among them depends on: • The amount of data that must be stored. • Whether the data must be modified frequently, rarely, or not at all. • How much data must be retrieved in a single access. • The importance of speed in reading and writing the data. • The importance of low cost. Rotating Magnetic Disks Most 2015 Secondary Storage uses rotating magnetic disks . 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

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  eBook - PDF

  Computer Systems Architecture

  • Aharon Yadin(Author)
  • 2016(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  311 C H A P T E R 9 Storage MASS STORAGE This chapter focuses and elaborates on various aspects of storage. By using the general architecture figure, we can relate to the storage devices (disks) in the system ( Figure 9.1 ). Storage Devices Every computer system, like any living creature, includes the means to store and later retrieve data. As seen in Chapter 5 , “Memory,” which discusses the memory hierarchy ( Figure 5.5 ), there are various levels of storage. In general, the memory—either the main memory or the various cache levels—is considered as the main level. However, these mem-ories are volatile and temporary and maintain the data stored as long as it was not replaced or as long as the system is operational. This volatile memory includes the first levels in the hierarchy (registers, cache, and main memory). For that reason, additional devices for long-term storage are required. The following levels of hierarchy are for media storage that does not need to be connected to an electricity source to maintain the data stored. Furthermore, the data is saved even if the system is nonoperational. The additional storage devices can be divided into several types, based on the access to the stored data and if they are online or not. Access to the devices can be • Serial access, which means that for reading a data item, all previous items have to be read or skipped. An example is various tape-based devices (similar to the tape cas-settes that were used for storing audio information). 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.

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  eBook - ePub

  Computer Systems Architecture

  • Aharon Yadin(Author)
  • 2016(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  9 Storage MASS STORAGE

  This chapter focuses and elaborates on various aspects of storage. By using the general architecture figure, we can relate to the storage devices (disks) in the system (Figure 9.1 ).

  Storage Devices

  Every computer system, like any living creature, includes the means to store and later retrieve data. As seen in Chapter 5 , “Memory,” which discusses the memory hierarchy (Figure 5.5 ), there are various levels of storage. In general, the memory—either the main memory or the various cache levels—is considered as the main level. However, these memories are volatile and temporary and maintain the data stored as long as it was not replaced or as long as the system is operational. This volatile memory includes the first levels in the hierarchy (registers, cache, and main memory). For that reason, additional devices for long-term storage are required. The following levels of hierarchy are for media storage that does not need to be connected to an electricity source to maintain the data stored. Furthermore, the data is saved even if the system is nonoperational.

  The additional storage devices can be divided into several types, based on the access to the stored data and if they are online or not. Access to the devices can be

  •  Serial access, which means that for reading a data item, all previous items have to be read or skipped. An example is various tape-based devices (similar to the tape cassettes that were used for storing audio information). 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.

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  No longer available |Learn more

  Outline of Computer Hardware

  • (Author)
  • 2014(Publication Date)
  • Learning Press

    (Publisher)

  ________________________ WORLD TECHNOLOGIES ________________________ Chapter 5 Secondary Storage 1. Hard disk drive Hard disk drive Interior of a hard disk drive Date invented December 14, 1954 Invented by An IBM team led by Rey Johnson A hard disk drive (HDD) is a non-volatile, random access device for digital data. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read and written on the platter by read/write heads that float on a film of air above the platters. ________________________ WORLD TECHNOLOGIES ________________________ The first HDD was invented by IBM in 1956. They have fallen in cost and physical size over the years while dramatically increasing capacity. Hard disk drives have been the dominant device for Secondary Storage of data in general purpose computers since the early 1960s. They have maintained this position because advances in their areal recording density have kept pace with the requirements for Secondary Storage. Form factors have also evolved over time from great standalone boxes to today's desktop systems mainly with standardized 3.5-inch form factor drives, and mobile systems mainly using 2.5-inch drives. Today's HDDs operate on high-speed serial interfaces; i.e., serial ATA (SATA) or serial attached SCSI (SAS). History Hard disk drives were introduced in 1956 as data storage for an IBM accounting computer) and were developed for use with general purpose mainframe and mini computers. Driven by areal density doubling every two to four years since their invention, HDDs have changed in many ways, a few highlights include: • Capacity per HDD increasing from 3.75 megabytes to greater than 1 terabyte, a greater than 270 thousand to 1 improvement. • Size of HDD decreasing from 87.9 cubic feet (a double wide refrigerator) to 0.002 cubic feet (2½-inch form factor, a pack of cards), a greater than 44 thousand to 1 improvement.

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  eBook - ePub

  Software-Defined Data Infrastructure Essentials

  Cloud, Converged, and Virtual Fundamental Server Storage I/O Tradecraft

  • Greg Schulz(Author)
  • 2017(Publication Date)
  • Auerbach Publications

    (Publisher)

  Chapter 7

  Storage Mediums and Component Devices

  Memory is storage, and storage is persistent memory.

  What You Will Learn in This Chapter

  • Data storage mediums provide persistent storage for data and applications.
  • Why there are different types of storage mediums for various applications.
  • Storage media and medium fundamentals and PACE characteristics.
  • Comparing storage mediums beyond cost per capacity.
  • Storage space capacity vs. I/O consolidation.
  • Storage device metrics that matter.
  • Looking beyond the interface.

  We are near the halfway point in this book, having covered the basic bits, bytes, blocks, and objects, file systems, access, servers, and I/O networking fundamentals. Let us now move deeper into the topic of storage, which is an extension of memory, which is storage; storage is persistent memory, memory is storage.

  This chapter looks at the mediums and basic component building blocks that get hardware and software defined into solutions or service. In subsequent chapters, we will look at how the storage components discussed here, along with server and network resources discussed earlier, get combined with data services and delivered as solutions. The storage components discussed are the key themes, buzzwords, and trends addressed in this chapter, including nonvolatile memory (NVM), storage class memory (SCM), hard disk drives (HDD), solid-state devices (SSD), hybrid, and NAND flash, among other related technologies and topics for enabling data infrastructures spanning physical, software-defined, virtual, container, and cloud environments.

  7.1 Getting Started

  A recurring theme in this book is that everything is not the same in data centers and data infrastructures. With different sizes and types of environments along with diverse applications, there is a need for various types of data infrastructure resources, including servers, input/out- put networking, and connectivity along with storage devices and mediums.

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