Editing Flat memory model (section)

===x86 segmented memory model===
{{Main|Memory segmentation|x86 memory models}}

*Similar to paged memory, but paging is achieved by the implicit addition of two relatively shifted registers: '''segment:offset'''
*Variable page boundaries, more efficient and flexible than the paged memory model
*Quite complex and awkward from a programmer's point of view
*More difficult for compilers
*Pages can overlap / poor resource protection and isolation
*Many to one address translation correspondence: Many '''segment:offset''' combinations resolve to the same physical address
*Greater chance of programming errors
*Implemented in the original Intel 8086, [[8088]], [[80186]], [[80286]], and supported by [[80386]] and all subsequent [[x86]] machines through to present day [[Pentium]] and [[Core 2]] processors. This memory model has remained ever since in the x86 machines, which now provide multi-mode operation and rarely operate in the compatible segmented mode.{{Clarify|date=July 2010}} See [[x86 memory segmentation]] for details.
*saves RAM by moving the segment address, this allows short jumps that require fewer bytes.

Within the x86 architectures, when operating in the [[real mode]] (or emulation), physical address is computed as:<ref>[http://www.deinmeister.de/x86modes.htm General description of Real Mode] "The physical address can be calculated as Value_in_segment_register{{not a typo| *}}<!-- it is a citation --> 16 + Value_in_offset_register."</ref>
:Address = 16 × segment + offset
(I.e., the 16-bit segment register is shifted left by 4 bits and added to a 16-bit offset, resulting in a 20-bit address.)