Notes: Storage & Communication Devices — Essential Concepts (Last-Minute Review)

HARDWARE STORAGE DEVICES

• Storage medium: physical material where data/programs are kept; cloud storage uses internet servers; media details are transparent to user.
• Storage device: hardware that records/retrieves items to/from storage media.
• Capacity units (bytes):
  • $\text{Kilobyte (KB)}: 10^3\text{ bytes} \ or \ 2^{10}\text{ bytes}$
  • $\text{Megabyte (MB)}: 10^6\text{ bytes} \ or \ 2^{20}\text{ bytes}$
  • $\text{Gigabyte (GB)}: 10^9\text{ bytes} \ or \ 2^{30}\text{ bytes}$
  • $\text{Terabyte (TB)}: 10^{12}\text{ bytes} \ or \ 2^{40}\text{ bytes}$
  • $\text{Petabyte (PB)}: 10^{15}\text{ bytes} \ or \ 2^{50}\text{ bytes}$
  • $\text{Exabyte (EB)}: 10^{18}\text{ bytes} \ or \ 2^{60}\text{ bytes}$
  • $\text{Zettabyte (ZB)}: 10^{21}\text{ bytes} \ or \ 2^{70}\text{ bytes}$
  • $\text{Yottabyte (YB)}: 10^{24}\text{ bytes} \ or \ 2^{80}\text{ bytes}$
• Volatility vs nonvolatility:
  • volatile: screen RAM; contents lost on power loss.
  • nonvolatile: storage retains data without power.
• Access time: time to locate and deliver data from storage to the processor.
• Hard Disk Drive (HDD): one/more magnetic platters; data stored on magnetics.
• Formatting: divides disk into tracks, sectors; clusters formed by multiple sectors.
• HDD characteristics: tracks, sectors, platters, form factor, read/write head, rpm.
• Head crash risk: head may contact platter; back up regularly.
• SSD (Solid State Drive): flash memory with own controller; advantages: $\text{faster access}$, $\text{lower power}$, $\text{faster transfer}$, no defragmentation, more durable, lighter, longer life.
• Memory card: removable flash storage (in devices/reader).
• USB flash drives: plug into USB ports.
• Cloud storage: internet service providing storage.
• Enterprise storage: hardware for heavy use, high efficiency/availability.
• NAS (Network-Attached Storage): storage server on a network for connected devices.
• SAN (Storage Area Network): high-speed network dedicated to storage.
• Tape: magnetic tape for large, archival storage.
• Magnetic stripe / Smart card: passive/embedded data carriers.
• RFID tag: radio memory chip with antenna; RFID reader reads data.
• NFC tag/device: chip+antenna for short-range communications; often self-adhesive.

HARDWARE COMMUNICATION DEVICES

• Digital communications: two or more devices transfer data, instructions, information.
• Example sending/receiving devices: servers, desktops, laptops, tablets, smartphones, headsets, etc.; transmission media include phone/power lines, cable, microwave, satellites.
• Network: collection of computers/devices connected to share hardware, data, software.
• Network types:
  • LAN: local area network
  • WLAN: wireless LAN
  • MAN: metropolitan area network
  • WAN: wide area network
  • PAN: personal area network
• Network architecture: client-server vs P2P.
• Network topology types: bus, star, ring, mesh, tree, line, hybrid; basic definitions:
  • Bus: all devices on a single cable
  • Star: devices connect to central hub/switch
  • Ring: devices connected in a loop
  • Mesh: multiple interconnections for redundancy
  • Tree: hierarchical star networks on a bus
  • Hybrid: combination of topologies
• Networking devices:
  • Router: routes packets between networks
  • Hub/Switch: central connection point for cables
  • Repeater: regenerates/extends signal range
• Transmission media:
  • Wired: carries one or more signals; bandwidth = data capacity; latency = signal travel time
  • Wireless: infrared, Bluetooth, Wi‑Fi (IEEE 802.11 variants), cellular, microwave, satellite
• Transmission bandwidth concepts:
  • Bandwidth: data-carrying capacity of a medium
  • Latency: time delay in a network path

WIRED AND WIRELESS TRANSMISSION MEDIA

• Cable types and typical transfer rates:
  • Cable varieties (example ranges):
  • Cable: $\text{256 Kbps to 100 Mbps or higher}$
  • DSL: $\text{256 Kbps to 8.45 Mbps}$
  • FTTP: $\text{5 Mbps to 300 Mbps}$
  • T1: $1.544\ \text{Mbps}$
  • T3: $44.736\ \text{Mbps}$
  • ATM: $155\text{ Mbps} \to 622\text{ Mbps} \ (up\ to\ 10\ \text{Gbps})$
• Physical media: twisted-pair, coax, fiber
  • Twisted-pair: common for landlines/LANs; color-coded conductors
  • Coaxial: copper center conductor with shielding
  • Fiber-optic: glass/plastic strands carrying light pulses
• Wireless transmission media: typical max transfer rates
  • Infrared: $\approx 115\text{ Kbps} - 4\text{ Mbps}$
  • Bluetooth: $\approx 1 - 24\text{ Mbps}$
  • 802.11 family: 11 Mbps (802.11b) to 7 Gbps+ (802.11ad); 802.11n: ~300 Mbps; 802.11ac: higher rates
  • UWB: $110 - 480\text{ Mbps}$
  • Cellular: 2G/3G/4G ranges (approx. Kbps to 100 Mbps+ depending on tech)
  • Microwave: very high rates; satellite links also used
• Wireless transmission topics:
  • Broadcast radio vs cellular radio
  • Satellite communications
  • GPS: receivers determine location via satellite signals

ADDITIONAL KEY CONCEPTS

• Backups: always keep backups of critical disks.
• Cloud/enterprise storage trends: scalable storage across networks and services.
• Quick recall terms: volatile vs nonvolatile, bandwidth, latency, topology, architecture.
• Summary for exam recall: Storage hierarchy (RAM vs HDD/SSD vs cloud), Network types and topologies, Transmission media and device roles.