The address bus is the set of wire traces that is used to identify which address in memory the CPU is accessing.
The number of wire traces in the address bus limits the maximum amount of RAM which the CPU can address.
CPU Address Bus Sizes
| CPU | Address Bus Size |
|---|---|
| 8086 | 20 bit |
| 8088 | 20 bit |
| 80286 | 24 bit |
| 80386SX | 24 bit |
| 80386DX | 32 bit |
| 80486SX | 32 bit |
| 80486DX | 32 bit |
| Pentium I | 32 bit |
| K6 | 32 bit |
| Duron | 32 bit |
| Athlon | 32 bit |
| Athlon XP | 32 bit |
| Celeron | 36 bit |
| Pentium Pro | 36 bit |
| Pentium II | 36 bit |
| Pentium III | 36 bit |
| Pentium 4 | 36 bit |
| Athlon | 40 bit |
| Athlon-64 | 40 bit |
| Athlon-64 FX | 40 bit |
| Opteron | 40 bit |
| Itanium | 44 bit |
| Itanium 2 | 44 bit |
Address Bus Memory Capacity Chart
| Address Bus Size | Maximum RAM |
|---|---|
| 20 bits | 1MB |
| 24 bits | 16MB |
| 32 bits | 4GB |
| 36 bits | 64GB |
| 40 bits | 1TB |
| 44 bits | 16TB |
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