Classify every cable you own by what it actually carries

short · 40 min · Objective 1.2

Task

Find out which of your cables carry data, which only carry power, and at what speed -- by measuring rather than by looking. Most people own at least one charge-only cable and do not know which one it is.

Steps

  1. Write lab/cables/inventory.csv with header id,connector_a,connector_b,length_cm,markings,guess and one row per cable. guess is what you expect it to be BEFORE testing.
  2. For each cable, connect a device that appears as storage and record in lab/cables/result.csv with header id,enumerated,speed,charges whether the device appeared, the negotiated speed reported by the operating system, and whether power flowed.
  3. Copy a file of at least 500 MB over each cable that enumerated, and record the observed rate in the speed column as MB/s rather than as a marketing name.
  4. Write lab/cables/surprises.md listing every cable whose result differed from your guess, with one line each on what the marking suggested and what the measurement showed.
  5. Label the charge-only cables physically, and record in lab/cables/labelled.txt how many you labelled.

Verify

awk -F, 'NR>1 && NF>=6 {n++} END {print n" cable(s) inventoried"}' lab/cables/inventory.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" cable(s) tested"}' lab/cables/result.csv
awk -F, 'NR>1 && tolower($2)=="no" {n++} END {print n+0" charge-only cable(s)"}' lab/cables/result.csv
awk -F, 'NR>1 {print $3}' lab/cables/result.csv | sort -u | wc -l
grep -c . lab/cables/surprises.md

Four or more cables inventoried and tested, at least two distinct speeds observed, and the surprises file non-empty. If no cable surprised you, test more cables -- the charge-only one is usually the one that came in a box with something else.

Notes

This is the lab readers report as most immediately useful. The labelled cables save time for years, and the measured speeds are what let you answer 'why is the external drive slow' without opening anything.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.