UMB
(Upper Memory Blocks)
     Also known as High RAM and Upper-Memory. Normally expanded memory only REQUIRES a 64K page frame. But, a lot of LIM 4.0 compatible expanded memory boards (such as Intel memory boards) automatically try to provide as large a page frame as possible, up to 128K (if there are no ROM's within this range also using some of this space), within the C000-DFFF range. These additional pages of expanded memory in the page frame can be used to create Upper Memory Blocks, which are blocks of memory that can be used to load device drivers and TSR's into them in order to free up more conventional memory for your applications. Basically, every extra page of expanded memory outside of the first 64K of the pageframe can be turned into a UMB. There are memory managers available that create these UMB's.

     UMB providers in 8088, 8086, and 80286 based systems:

  1. QRAM
  2. MOVEM
     These memory managers require that the available Upper Memory Blocks first be made mappable by the combination of a LIM 4.0 Expanded Memory Manager and a memory card such as Intel's EMM.SYS device driver and an Intel Above Board. The Above Board Plus and Above Board Plus 8 can map extra 16K blocks of memory within the C000-DFFF address range beyond the first 64K (which has to remain intact so that applications that use expanded memory will still be able to use it).

     UMB providers in i386 and i486 based systems:

  1. EMM386.SYS provided with DOS 5.0
  2. QEMM
  3. 386MAX
     These memory managers do not require LIM 4.0 expanded memory board because the i386 and i486 microprocessors have "mapping" capabilities built into them. 386 memory managers simply use extended memory to emulate expanded and also UMB's.
Typical PC memory map

Main Menu
BUG Computer Club Home Page

Valid HTML 4.01!
Last Update: 2:20 PM 11/8/01