A+ Cable, Storage & RAID Master Notes

Fiber-Optic Basics

• "LED light with the larger core" = multimode fiber (MMF)
  • Multiple light paths ⇒ more simultaneous signals
  • Optimized for short-range, in-building links; cheaper than single-mode
• Contrast: laser-driven single-mode (not detailed in the clip) = tiny core, long distances

USB Cable Landscape

• Know them by sight & name – exam may show pictures
• Standard-A
  • Classic flat rectangle; historically on every PC/peripheral
• Standard-B
  • Squarish; common on printers, external HDD bays, pro-audio gear (phantom-powered interfaces, MIDI controllers)
• Mini-B
  • Older headsets, early digital cameras/chargers
• Micro-B
  • Widely used on small peripherals & LED lighting accessories
• USB-C
  • Reversible, on both ends, rapidly replacing A/B; many laptops/phones ship C-to-C only
• Color coding (manufacturer-dependent but common):
  • Blue/Teal = USB 3.x high-speed
  • Orange = “Always-On” power delivery
  • Plain Black/White = 2.0/low speed

Serial & Specialty Cables

• DB-9 (DE-9)
  • RS-232 serial console for network gear
• Thunderbolt 4
  • $40\,\text{Gb/s}$, uses USB-C shell; non-proprietary (often seen on Macs)

Video Interfaces

• HDMI vs DisplayPort (DP)
  • HDMI: mainstream consumer; carries audio + CEC
  • DisplayPort: gamers like higher throughput, supports daisy-chaining (Multi-Stream Transport)
    • One DP cable PC→Monitor 1; short DP jumpers Mon 1→Mon 2→Mon 3
  • DP locking latch → press release button before pulling to avoid motherboard damage
• Mini DisplayPort / Mini HDMI exist; rarely tested
• DVI
  • Recognize by odd grids of pins + long flat blade
  • Letter tells you signal: A = analog, D = digital, I = integrated (both)
• VGA (DB-15)
  • Legacy analogue, video-only (needs separate audio)

Converter/Adapter Scenarios

• HDMI↔DVI, DVI↔VGA, USB↔Ethernet, etc.
  • Classic exam story: broken RJ-45 → use USB-to-Ethernet dongle

Copper Data & Power Inside PCs

• SATA
  • Serial ATA data (7-pin “L”) + SATA power (15-pin “L”) on HDD/SSD
• Molex 4-pin
  • Legacy HDD power; “Molex” is actually the brand, but exam treats it as the 4-pin connector that SATA replaced
• Modular vs Non-modular PSU
  • Modular lets you unplug unused Molex/SATA strands for airflow
• Lightning = Apple-only mobile connector

Fiber Terminations (must ID by image)

• LC – “Lucent / Locking / Little Connector”: tiny, trigger latch on top (locking)
• SC – “Square Connector / Subscriber Connector”: big square body
• ST – “Straight Tip”: bayonet, metal barrel with the pointy tip
• Pairs are common but each plug can be unclipped into singles

Networking & Telecom Tools (quick hits)

• 110 block + punch-down tool → still high miss-rate on exams
• BNC coax: rare in IT exams but still used for pro-video/RF antennas

Memory (RAM)

• Volatile – data lost when power drops
• Analogy: RAM = worktable for the CPU “little man in the box”
• DDR SDRAM DIMM: Dual Data-Rate Synchronous DRAM Dual Inline Memory Module
  • Clock edge transfers $\rightarrow$ DDR sends two words per tick
• Form factors
  • DIMM (desktop) vs SO-DIMM (Small Outline, laptops/thin clients)
• Generations (no pin-count memorization required)
  • DDR3 < DDR4 < DDR5 (up to $64\,\text{Gb}$ per chip)
  • Not cross-compatible – notch/key moves every gen
• ECC RAM
  • Extra chip for parity/error correction; slower & pricier; typical in servers; avoid when building consumer PC PBQs
• Channels
  • Single, Dual (common), Triple/Quad (workstations/servers)
  • Matched sticks must be installed in documented slots (color-coded) or dual-channel won’t activate

Non-Volatile Storage – HDD

• Parts: platters, spindle, actuator arm, PCB
• Mechanical downsides
  • Vibration-sensitive, heat, slow seek; drop == head crash (scratches platter)
• Warning signs: grinding/clicking ⇒ backup immediately
• RPM classes: $5400$, $7200$, $10000$ RPM ⇒ higher RPM = lower latency, faster throughput
• Form factors: 3.5" (desktop/server), 2.5" (laptop, also fits desktops)
• Cost/GB still lowest; huge capacities (multi-PB in enterprise arrays)
• External USB/SATA caddy converts an internal drive to a removable for data rescue/migration

Solid-State Storage

• SSD advantages: no moving parts, silent, cool, shock-resistant, ~10× faster
• NVMe (Non-Volatile Memory Express)
  • Uses PCIe lanes – speeds $\approx 3000{-}7000\,\text{MB/s}$ vs SATA SSD $\approx 550\,\text{MB/s}$
• M.2 slot (form factor, not protocol)
  • Insert at ~45° → push flat → secure with tiny screw (spring-loaded)
• SAS (Serial Attached SCSI)
  • Enterprise drive interface, daisy-chains multiple drives; rare on A+ but know it exists

Backup vs Redundancy

• RAID ≠ Backup
  • True backups often on magnetic tape libraries; rotated on schedules (grandfather-father-son, etc.)

RAID Levels (must master)

Detailed mental model

• RAID 0 example: two $5\,\text{TB}$ drives ⇒ $10\,\text{TB}$ usable; any single-drive loss destroys array
• RAID 1: two $5\,\text{TB}$ drives ⇒ $5\,\text{TB}$ usable; can lose one entire drive seamlessly
• RAID 5: three $5\,\text{TB}$ drives ⇒ $10\,\text{TB}$ usable (third holds distributed parity); any one failure is ok
• RAID 6: four $5\,\text{TB}$ drives ⇒ $15\,\text{TB}$ usable; two failures ok
• RAID 10: four $5\,\text{TB}$ drives ⇒ $10\,\text{TB}$ usable; stripes across two mirrored pairs; must not lose both drives in same mirror

Practical nuggets

• Always verify array type (0/1/5/6/10) before hot-swapping in data centers; RAID 5 single-disk tolerance means accidental 2-disk pull destroys data
• Many enterprise shelves let admins “blink” the failed drive LED – snap a photo, get remote confirmation (CYA)

Safety & Handling Tips

• Anything with a lock/latch (DisplayPort, LC fiber) → depress before pulling
• Never force connectors or RAM: notch = key; wrong orientation ruins slot/board
• Frequent plug/unplug damages solder joints on laptop motherboards (charging, video); treat ports gently

Miscellaneous Quick Facts

• Punch-down vs crimp – 110 block uses punch-down, not crimp tool
• Port flap in switches = intermittent link; term exists despite some instructors’ doubts
• Tape-drive cartridges look like mini VHS/8-track; massive capacity, slow access
• In British English "redundant" = laid-off; helpful mnemonic that redundant disk isn’t required for operation but there for safety