DOS developers are familiar with the segmented architecture of the 8086 processor which complicates address arithmetic and limits any one data object to 64KB. This limit can be worked around with some difficulty, but still presents an obstacle to efficient DOS programming.
The UNIX operating system running on
the 80386, 80486, and Pentium processors
uses 32-bit mode 32-bit registers,
and so the segment size is 4GB.
Because of this large address space,
programmers do not need to consider segment registers.
Indeed, segment register manipulation
is disallowed in user-level programs.