Address Lines & Memory Size

How many address lines do you need?

Each address line doubles the number of locations you can address. With n address lines, you can address 2n unique locations.

n address lines → 2n addressable locations

Landmark Values (memorize these)

10
lines
1 K
1,024
16
lines
64 K
65,536
20
lines
1 M
1,048,576
30
lines
1 G
1,073,741,824
32
lines
4 G
4,294,967,296
40
lines
1 T
1,099,511,627,776

Try It

Address Lines
=
Memory Size
1 K
210 = 1,024 locations
1 48

Mental Math Shortcuts

①
Anchor on 10 = 1K. This is your starting point. Every 10 additional lines multiplies by 1,000 (roughly).
②
The K-M-G-T ladder: 10→1K, 20→1M, 30→1G, 40→1T
③
Quick adjustments: Each additional line doubles the size. So 11 lines = 2K, 12 lines = 4K, 13 lines = 8K.
④
Why 32 bits = 4 GB: 32 = 30 + 2, so that's 1G × 4 = 4G. This is why 32-bit systems maxed out at 4 GB RAM.
⑤
Working backwards: Need 256 locations? That's 28, so 8 address lines. Need 1 million? That's ~220, so 20 lines.