Physical Memory

A physical address is used to access a byte in RAM.  The address is placed onto the address lines of the processor.  The number of address lines defines the physical address space.

• 8086 and 8088 spot 20 address lines (1MB)
• 286 has 24 address lines (16MB)
• 386 DX, 486 DX and Pentium have 32 address lines (4GB)
• Pentium Pro has 4 more address lines (total 36) which known as Physical Address Extension (PAE) facility  and can address up to 64GB