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DOS学习入门 & 精彩文章（教学室） » What’s the difference between EMS and XMS?

Floor1　Greentea	Posted 2005-03-27 00:00
初级用户　Posts 4　Credits 120
I remember EMS and XMS being called “expanded memory” and “extended memory,” but I’m not clear on what the difference really is, so I wanted to ask. Is there any detailed documentation?

Floor2　GOTOmsdos	Posted 2005-03-29 00:00
铂金会员　Posts 1,827　Credits 5,154
Older DOS programs need EMS, limited to 32MB EMS came first, then XMS

Floor3　shijianxin	Posted 2005-08-08 02:05
初级用户　Posts 52　Credits 115
Originally posted by GOTOmsdos at 2005-3-29 00:00: Older DOS programs need EMS, limited to 32MB EMS came first, then XMS

Floor4　Michael	Posted 2005-08-09 20:31
钻石会员　Posts 3,041　Credits 10,056
EMS is read using page mapping, and when reading or writing EMS it still needs to occupy part of the low address space. That’s why if emm386 is used with the ram parameter, the available conventional memory decreases. So I usually use the noems parameter.

Floor5　johnsonlam	Posted 2005-08-11 13:41
银牌会员　Posts 497　Credits 1,410　From 九龍，香港
Originally posted by Greentea at 2005-3-27 12:00 AM: I remember EMS and XMS being called “expanded memory” and “extended memory,” but I’m not clear on what the difference really is, so I wanted to ask. Is there any detailed documentation? Extend requires Protectd Mode, needs a 286 or above, direct linear access, there is no such thing as "paging" Expand only needs Real Mode, even an 8086 can use it, it divides memory into 64K "pages", and uses pages for access

Floor6　henrya2	Posted 2007-06-16 17:38
中级用户　Posts 171　Credits 486
Seems like you got it backwards, right? XMS came first and then EMS.