Pentium addressing capability — maximum directly addressable memory space Considering a 32-bit physical address bus, how much memory can a Pentium address?

Introduction / Context:
The number of address lines determines the maximum directly addressable memory space. For a processor with a 32-bit physical address bus, the theoretical addressable range is a key design constraint for operating systems and hardware designers.

Given Data / Assumptions:

• Pentium-era processors provide 32 physical address lines in mainstream configurations.
• No paging tricks or segmentation limits are being considered; we refer to raw physical address space.
• Each unique address selects one byte.

Concept / Approach:

The physical address space equals 2^(number of address lines). With 32 address lines, that becomes 2^32 byte addresses. Converting 2^32 bytes gives 4,294,967,296 bytes, which equals 4 GB. System implementations may reserve ranges for memory-mapped I/O, but the theoretical maximum remains 4 GB for a 32-bit physical address bus.

Step-by-Step Solution:

Verification / Alternative check:

Motherboard documentation from the Pentium era commonly lists 4 GB as the maximum physical address range, with practical limits based on chipset and DIMM support.

Why Other Options Are Wrong:

1 MB reflects early 20-bit address spaces (8086 real mode). 1 GB and 2 GB are subsets of the full 4 GB capability.

Common Pitfalls:

Confusing virtual address space limits with physical addressable memory; operating system choices do not change the bus width capability.

Final Answer:

4 GB