XMS is an alternative method for accessing memory about the 1 MB boundary in real-mode DOS. Unlike EMS, it does not require a 64K pageframe in low memory, making it generally more compatible. Depending on the application, it can also be faster than EMS, because EMS is emulated using XMS on most computers.
Available for download are the official XMS 2.0 and 3.0 specifications, as well as the Microsoft XMS distribution disk. (Note that Windows NT/2000/XP only support XMS 2.0 functions.)