HMA
(High Memory Area)
     HMA refers to a specific way of accessing the first 64Kb of Extended Memory. Normally, for an 80286 to access extended memory, the processor has to switch into what is called "protected mode", make the extended memory access, and then be reset so that it returns to "real mode" (which is the mode that DOS runs under). This whole operation takes time. There is, however, a "back door" method to access the first 64K of extended memory without switching the processor into protected mode. What manages this special way of accessing the first 64K of extended memory is something called an HMA provider (also sometimes called an A20 handler).

     Device drivers that create the HMA in 80286-based systems:

  1. HIMEM.SYS provided with DOS 5.0
  2. QEXT.SYS from Quarterdeck Office Systems
  3. MOVEM.MGR from Qualitas

     Device drivers that create the HMA in i386-based systems:

  1. HIMEM.SYS provided with DOS 5.0
  2. QEMM386 from Quarterdeck Office Systems
  3. 386MAX from Qualitas

Main Menu
BUG Computer Club Home Page

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