Bytes, KB, MB, GB, TB

Two Systems, One Confusion

 DECIMAL (SI) — storage marketing & networking   BINARY (IEC) — memory & OS
 1 KB = 10³  B = 1,000                           1 KiB = 2¹⁰ B = 1,024
 1 MB = 10⁶  B                                   1 MiB = 2²⁰ B ≈ 1.05 MB
 1 GB = 10⁹  B                                   1 GiB = 2³⁰ B ≈ 1.07 GB
 1 TB = 10¹² B                                   1 TiB = 2⁴⁰ B ≈ 1.10 TB

 practical rule for estimation: treat them equal (±7–10% is noise at
 design precision) — but know which one a "1 TB drive" advertises

Cloud storage bills in decimal; RAM sizing lives in binary; the difference never changes an architectural verdict.

Power-of-Two Anchors

Binary fluency speeds every estimate:

Power	Value	Anchor
2¹⁰	~10³	1K
2²⁰	~10⁶	1M
2³⁰	~10⁹	1G
2³²	~4.3×10⁹	32-bit address space / IPv4 count
2⁶⁴	~1.8×10¹⁹	64-bit space; “never runs out” territory

The 2³² anchor explains real history: IPv4 exhaustion (~4.3B addresses) and the 2038 epoch problem — powers of two are not trivia, they are capacity walls.

Record-Size Intuition

Storage estimates die on bad per-record guesses. Calibrate with typical payloads:

Record type	Realistic size
Session token row	~200–500 B
User profile row	~1–2 KB
Trip/order record with overhead	~1 KB
Chat message	~200 B–1 KB
Product catalog entry + metadata	~5–20 KB
1080p video minute	~50–100 MB
App page HTML	~100–500 KB

Rule of thumb for relational rows: count the fields, assume ~50–100 bytes each with overhead, round up. Being within 2x is fine — replication and index multipliers dominate anyway.

Quick Conversions Worth Memorizing

 1 day          = 86,400 s        ≈ 10⁵ s
 1 hour         = 3,600 s         ≈ 4×10³ s
 1 GB/day       ≈ 11.6 µB/s sustained flow... rather:
 1 MB/s sustained × 1 day       ≈ 86 GB/day
 1 Gbps link    = 125 MB/s       ← divide by EIGHT, always
 1 TB           = 1,000,000 MB   = 16 days of 1 MB/s streaming
 
 growth check: X GB/day × 365 ≈ X/1.6 TB/year (mental shortcut)
   e.g., 20 GB/day → ~12.5 TB/year ✓ (matches RideShare math)

Interview Framing

Unit slips destroy credibility faster than wrong conclusions: saying “1 Gbps = 1000 MB/s” ends conversations. Strong candidates convert aloud once (“payloads in bytes, links in bits — dividing by eight”) and then move on. The tested skill isn’t reciting prefixes; it’s producing defensible record sizes and converting them into yearly totals without a calculator.