25th Anniversary of the Personal Computer" 4200

Philip Homburg

Peter Flbutt

The 286 segmented memory management has been much maligned. I may be the only programmer in the world who likes it. It does have some limitations which seem odd today, but which were somewhat reasonable at the time: Each segment is limited to 64 KB. But remember that on the early MacIntosh systems, a segment was limited to 32 KB, and people found that they could live with that.

I worked on an embedded project, where we used a 386 CPU in 286 mode. We used a fairly standard "DOS Extender" (PharLap), and for debugging, I wrote a version of malloc() where each malloc'ed object was in its own segment. Found a lot of addressing errors very fast, when we turned that on.

Around the time that the 386 came out, the affordable unix ports were also becoming available, and they all favored a flat memory model - I think because that made for a simple, portable paging system, since it made it similar to the MMUs of all the other minis and superminis. Using segments intelligently probably breaks a lot of otherwise portable unix code.

Lars Poulsen