Secondary Storage – Comprehensive Exam Notes

Learning Objectives

  • After studying this chapter you should be able to:

    • Distinguish primary vs. secondary storage.

    • Identify and explain four core characteristics of secondary storage: media, capacity, storage devices, access speed.

    • Define, describe and evaluate solid-state storage technologies (SSDs, flash memory cards, USB flash drives).

    • Diagram hard-disk geometry: platters, tracks, sectors, cylinders; explain magnetic recording and density.

    • Compare five performance-enhancement techniques: disk caching, RAID, hybrid drives, file compression & decompression.

    • Define and differentiate optical storage formats (CD, DVD, Blu-ray) and disc formats (ROM, R, RW).

    • Contrast internal, external and network drives.

    • Explain cloud storage and list major cloud-storage services.

    • Describe enterprise/mass-storage solutions—file servers, NAS, RAID, organizational cloud, SAN.

Why Secondary Storage Matters

  • Vital for persistence of data: photos, videos, apps, homework, OS‐files.

  • Running out of space ≈ phone cannot record video, laptop cannot install apps, tablet slows.

  • Future visions include holographic or organic (DNA) media holding the entire Internet in your pocket.

  • Nicole (disaster-recovery specialist) stresses that backups & cloud services keep organisations operational after disasters.

Primary vs. Secondary Storage

  • Primary (RAM)

    • Volatile; erased when power fails.

    • Limited capacity; must load program/data before CPU can process.

  • Secondary

    • Non-volatile; retains info when power is off.

    • Much larger; uses write (save) & read (retrieve) operations.

Key Characteristics of Secondary Storage

  • Media – physical material holding bits.

  • Capacity – maximum data volume a medium stores (e.g., 700 MB700\ \text{MB} CD, 4.7 GB4.7\ \text{GB} DVD, 50 GB50\ \text{GB} BD).

  • Storage Devices (Drives) – hardware that reads/writes the media.

  • Access Speed – time to locate & deliver requested data (affected by device type & enhancements).

Solid-State Storage

  • Uses flash memory; combines RAM’s rewritability with ROM’s persistence.

  • No moving parts ⇒ shock-resistant, silent, energy efficient, faster than magnetic drives.

Solid-State Drives (SSDs)

  • Store charges representing binary codes; e.g., letter A encoded as eight +/- charges.

  • Internal (within system unit) or external (USB/Thunderbolt enclosure).

  • Popular in smartphones, tablets, ultrabooks, gaming rigs—high speed, low power.

Flash Memory Cards

  • Tiny removable SSDs for cameras, phones, GPS. Increase or transport device storage.

  • Slide inside device slots or card readers.

USB Flash Drives

  • Key-ring size; plug directly into USB port.

  • Capacities from 1 GB1\ \text{GB} to 2 TB2\ \text{TB}+.

  • Security/ethics scenario: attackers leave “free” infected drives—never plug unknown USBs.

Troubleshooting / Tips

  1. Accidentally deleted files → run recovery utilities such as Disk Drill or Recuva.

  2. Drive not recognised → test USB port with other device; isolate port vs. flash-drive failure.

  3. Physically damaged drive → consider costly professional chip-level recovery.

Hard-Disk Drives (HDDs)

  • Contain spinning platters with magnetic coating; read/write heads move across.

  • Record 1s & 0s by flipping magnetic polarity.

  • Density = closeness of magnetic charges; higher density ⇒ higher capacity.

Geometry

  • Tracks – concentric circles.

  • Sectors – wedge-shaped subdivisions of tracks.

  • Cylinder – set of vertically aligned tracks across platters (addressing aid).

  • Formatting creates these logical structures.

Types

  • Internal HDD – inside system unit; stores OS & major apps.

  • External HDD – USB/Thunderbolt attached; slower but removable for backups, transport, security.

  • Network Drive – remote over LAN/WAN; prioritises capacity & durability over speed.

Performance Enhancements

  • Disk Caching – RAM cache stores anticipated disk blocks → up to 30 %30\ \% faster throughput.

  • Hybrid Drives – small SSD cache + large HDD; OS/apps on SSD, media files on HDD.

  • RAID (Redundant Array of Inexpensive Disks)

    • Multiple inexpensive disks operate as one logical unit.

    • Benefits: expanded capacity, fault tolerance (mirroring/parity), faster read/write.

  • File Compression / Decompression

    • Algorithms replace repetitive patterns with tokens; often shrink size to 14\tfrac{1}{4} original.

    • Saves disk space & accelerates Internet transfers.

Optical Discs

Data Representation

  • Laser burns pits (bumps) and leaves lands (flats); reflection differences → binary.

  • Single spiral track divided into equal sectors (vs. concentric HDD tracks).

Formats & Capacities

Medium

Typical Capacity

Common Uses

CD

700 MB700\ \text{MB}

Music, legacy software

DVD

4.7 GB4.7\ \text{GB}

Movies, software installers

Blu-ray (BD)

50 GB50\ \text{GB}

Hi-def video, large games

Ultra HD Blu-ray (UHD BD)

100 GB100\ \text{GB}

4K4\text{K} video

Disc Recording Types

  • ROM – factory pressed; user cannot alter (e.g., commercial movie DVD).

  • R (Recordable) – write once, read many (ideal archival, e.g., CD-R family photos).

  • RW / RAM (Rewritable) – erasable & rewrite-capable; good for iterative backups.

Capacity-Boost Methods

  • Double-sided discs: data on both surfaces (e.g., 9.4 GB9.4\ \text{GB} DVD).

  • Multi-layer discs: stacked recording layers (e.g., BD up to 128 GB128\ \text{GB}).

Cloud Storage & Cloud Computing

  • Internet-hosted “cloud” servers deliver apps (SaaS) and provide online storage accessible anywhere.

Advantages

  • Maintenance: provider handles backups, patches, encryption.

  • Scalability/Upgrades: near-infinite space; hardware failures hidden from user.

  • Sync & Collaboration: real-time file sharing across devices & users.

Disadvantages

  • Access Speed limited by Internet bandwidth—usually slower than local storage.

  • Security/Privacy depend on provider policies; potential compliance concerns.

Major Services

  • Dropbox, Google Drive, Microsoft OneDrive, Amazon Drive, Apple iCloud.

Mobile-Data Tips (reduce cellular overages)

  1. Monitor per-app data usage (Settings → Data Usage / Cellular).

  2. Restrict background data (Android Data Saver; iOS Background App Refresh).

  3. Prefer Wi-Fi for large cloud syncs; specify offline files.

Choosing a Provider (Making IT Work for You)

  • Match file types (photos → Flickr, music → Google Play, docs → OneDrive).

  • Integrate with software tools (Office 365 ⇔ OneDrive; Google Docs ⇔ Drive).

  • Align with hardware ecosystem (iOS ⇔ iCloud; Android/Chrome ⇔ Drive).

  • Consider sharing model & recipients’ tech skills.

  • Use free trials; test across devices & scenarios.

Mass Storage & Enterprise Solutions

  • Mass Storage: enormous secondary storage volumes needed by organisations.

  • Enterprise Storage System: coordinated strategy ensuring efficient, secure, centralised data.

Components

  • File Servers – dedicated computers housing large shared directories.

  • Network Attached Storage (NAS) – simplified, affordable file server for homes/SMBs; fewer admin tools.

  • Enterprise RAID Systems – large-scale, redundant disk arrays safeguarding data in transit across network.

  • Organisational Cloud Storage – private/high-speed links to remote server farms.

Storage Area Network (SAN)

  • High-speed network linking remote storage to servers so it appears as local disks.

  • Provides block-level access, concurrency control, and off-site data housing while maintaining performance.

Ethics, Privacy & Security

  • Cheap storage ⇒ persistent digital footprints; difficult to erase embarrassing media.

  • Debate: “Right to be Forgotten” vs. permanence of Internet record.

  • Cloud liability: if professional stores confidential client data in cloud and it leaks—who is responsible?

  • USB-flash malware attacks highlight supply-chain and social-engineering risks.

Career Spotlight – Disaster Recovery Specialist

  • Role: design contingency plans; back up & restore systems after disasters.

  • Skills: networking, security, database admin, calm communication under stress.

  • Education: associate/bachelor in IS or CS; experience valued.

  • Salary range: 70,500–87,000 $per year70{,}500\text{–}87{,}000\ \$ per\ year; opportunities to advance into upper management.

Future Trends in Secondary Storage

  • Heat-Assisted Magnetic Recording (HAMR)

    • Laser heats nano-spots allowing denser magnetic bits ⇒ projected ×50\times50 capacity.

  • 3D XPoint / Intel Optane

    • Vertical multilayer flash cells; non-volatile with near-RAM latency.

  • DNA Storage

    • Encoding digital bits as nucleotide sequences.

    • 2017: 215 PB/gram215\ \text{PB/gram} proof-of-concept; 2019: automated read/write prototypes.

  • Question: Will costs of molecular techniques fall enough to supplant magnetic/flash, or will we enhance existing SSD/HDD tech?

Concept-Check Q & A (Self-Study)

  • What differentiates volatile and non-volatile memory?

  • Name and explain the four characteristics of secondary storage.

  • Contrast SSDs with HDDs in speed, durability, power, cost, capacity.

  • Define track, sector, cylinder; why are cylinders important?

  • How does disk caching mimic CPU cache behaviour?

  • What does RAID 5 provide that simple disk mirroring does not?

  • List pros/cons of cloud storage for sensitive corporate data.

  • Which optical-disc format can store 4K4\text{K} content and how?

  • Describe a real-world scenario where a SAN adds value over local DAS (direct-attached storage).

End of Study Notes