Can someone explain to me in plain modern-day English what exactly the difference is between expanded and extended memory??????????????????

Yeah me too.

Well, sure, I have way too much time on my hands. That's why I wrote all this bullsh!t down in Social Studies class while my teacher rambled on and on and on and on about junk. Here goes... Extended memory typically refers to _physical memory_ located above 1 meg in the system memory (at the top of Reserved memory, not Upper or High memory for your information (Reserved memory is the physical division, while upper\high memory is the logical memory space there where other memory has been mapped)). This is accessed through hardware functions 15h and 81h, not hardware gate A20 address line. When the processor is in Real mode, this cannot be addressed, only accessed. With the exception of Flat Real mode, in which the segment size is changed to 4 gigs and it all can be addressed that way. But, in protected mode, 4 gigs of physical memory can be addressed. Typically, Extended memory is accessed through A20 and that is called XMS (Lotus\Intel\Microsoft\AST eXtended Memory Specifications), as this is a better routine than 13h, where there aren't exactly any rules about usage. XMS then can be used for whatever - being mapped to the reserved memory space (between 640K and 1M) as upper memory when the CPU's in Virtual 8086 Address Mode (aka V86), as an emulation of Expanded (EMS) memory (don't worry I'll get to all that later), and for other crap like disk caches and print spoolers and RAM disks. Got that all? Extended is the physical memory, at absolute locations, while XMS is the logical heap of memory that is really Extended memory accessed through A20. I don't want to go into anything about the HMA or Conventional memory...but if you make me mad, I will. Expanded memory (Expanded & EMS are about the same, luckily): EMS was developed long before XMS. It originally came only on hardware memory boards and was for the 8086 and 8088 processors, which could access only 1 meg of memory normally. These, in simple, copied physical pages of memory which couldn't be accessed by the processor, but which COULD be accessed by the memory board, to an area which the processor could access, which had to be within the 1 meg address space. Now, EMS was divided into 16K pages, and there was a 64K area in the first meg of physical system memory, which was called the "page frame". It had 4 pages, and programs could request that a page be mapped in and out of those 4 physical pages, write to them, etc. and then everything would stay on them when mapped in\out. So this enabled the 8086\8088 to access up to 32 megs of memory. Then processors drew on, with the 286, which could access 16 megs of memory, so EMS could be simulated with extended memory. However, not all functions were supported, and it was slow. Then came 386\above. These could access 4 gigs and had mapping ability, which made them almost as fast as a true EMS board. But more functions could be emulated and you could use a full 32 megs of emulated EMS. So true EMS boards don't exist much anymore, too expensive, etc. Oh, here are all the Lotus\Intel\Microsoft EMS 4.0 functions: 1A get EMM status 1B get EMM status w\ interrupt vector 2A get page frame seg 3A get free page count 3B get used page count 3C get total page count 4A allocate pages to handle 5A map\unmap page to page frame 6A free a handle 7A get LIM EMS version number 8A save memory mapping context w\ handle 9A restore memory mapping context w\o handle 10 & 11 existed only in earlier versions 12A get number of open handles 13A get pages used by handle 14A get pages used by all handles 15A get mapping context 15B set mapping context 15C get current map 15D get size for 15A\B 16A get partial mapping context 16B set partial mapping context 16C get partial mapping context size 17A map\unmap several pages 18A resize handle 19A get handle attrib 19B set handle attrib 19C see if attribs supported by hardware 20A get handle name 20B set handle name 21A get arrraw of all numbers\handles 21B get # of handle name given 21C get number of handles supported by system 22A alter map jump 23A alter map call 23B get number of bytes pushed onto stack when 23A is called 24A copy memory region 24B exchange mem region 25A copy entries from mappable regsion 25B get array of mappable pages 25C get number of mapped pages in mem 26A get free raw page count ...and so on to 30C... all this junk about alternate register sets and DMA register sets, blah blah. Good night people.......

woh, tough to argue with all that, =)

Extended/Expanded Memory for dummies: More recent DOS programs tend to utilize the more dynamic Extended memory. Older DOS programs, like our beloved fits-on-a-floppy Lotus 1-2-3, requires the older Expanded memory blocks. Emm386.exe allocates memory for either/both types per switches in the config.sys statement.

Extended memory (XMT) is the memory above 1 megabyte. Windows uses this and many commands in DOS 6.2 and up access it. Expanded memory fits through a 64 kbyte page in the first 1 megabyte of memory. It came into being first. In early computers through 286 there was no memory above 1 megabyte, but you could get memory cards that fit in an ISA slot. This card was accessed through that 64K "page". Some programs need expanded memory but they are very old. Some other programs can use it if available.

Fred 6008 did a great job of describing this. I'll add a little bit to his post: 1. As mentioned by Fred, expanded memory is the oldest method for using memory above 640k and emm386.exe does this. 2. himem.sys is the XMS (extended) memory manager used by today's newer software. It controls memory above 1mb. However, himem.sys can simulate expanded memory if you have old software that needs it. Using the "noems" command when loading himem.sys will eliminate that. If you don't use old software, you do not need expanded memory. All modern computers must have extended (XMS) memory.