Wireless networking

802.11a

5 GHz, 54 Mbps

802.11b

2.4 GHz, 11 Mbps

802.11g

2.4 GHz, 54 Mbps

802.11n

2.4 GHz & 5 GHz (dual-band), up to 600 Mbps, MIMO

802.11ac

5 GHz only, 6.933 Gbps, MU-MIMO

802.11ax

2.4 GHz & 5 GHz (dual-band), 9.6 Gbps

2.4 GHz Wi-Fi

• ✅ Longer range (travels further)

• ✅ Better penetration through walls/obstacles

• ❌ Lower speeds compared to 5 GHz

• ❌ More interference (microwaves, Bluetooth, cordless phones, etc.)

• ~14 channels (only 3 non-overlapping in the U.S.: 1, 6, 11)

5 GHz Wi-Fi

• ❌ Shorter range than 2.4 GHz

• ❌ Weaker penetration through solid objects

• ✅ Higher data rates (faster speeds)

• ✅ More channels available (reduces interference and congestion)

+12 VDC

Used by motors (hard drives, fans, optical drives), PCIe power, some CPUs

+5 VDC

Legacy logic circuits, older drives, some USB power

+3.3 VDC

Modern logic circuits, RAM, newer CPUs, expansion cards

+5 VDC

(standby power) → Keeps system in low-power state (Wake-on-LAN, etc.)

-12 VDC

Legacy, older serial ports (rarely used today, but still part of ATX spec)

What was the primary purpose of 2G cellular networks?

Digital voice (first digital cell standard), low data speeds.

Which cellular generation introduced mobile broadband, mobile web and video calls

3G

4G

(LTE, LTE-A) → High-speed broadband, supports HD streaming

5G

Gigabit speeds, ultra-low latency, supports IoT/large-scale device connectivity

When measuring a cloud file-sync app’s performance, which resource matters MOST?

I/O bandwidth (how fast data can move in/out of the cloud).