Page "X86 memory segmentation" Paragraph 3

Because of the way the segment address and offset are added, a single linear address can be mapped to up to 4096 distinct segment: offset pairs.

For example, the linear address 08124h can have the segmented addresses 06EFh: 1234h, 0812h: 0004h, 0000h: 8124h, etc.

This could be confusing to programmers accustomed to unique addressing schemes, but it can also be used to advantage, for example when addressing multiple nested data structures.

While real mode segments are always 64 KiB long, the practical effect is only that no segment can be longer than 64 KiB, rather than that every segment must be 64 KiB long.

Because there is no protection or privilege limitation in real mode, even if a segment could be defined to be smaller than 64 KiB, it would still be entirely up to the programs to coordinate and keep within the bounds of their segments, as any program can always access any memory ( since it can arbitrarily set segment selectors to change segment addresses with absolutely no supervision ).

Therefore, real mode can just as well be imagined as having a variable length for each segment, in the range 1 to 65536 bytes, that is just not enforced by the CPU.