
HIMEM.SYS

HIMEM.SYS is a DOS device driver which allows DOS programs to store data in extended memory according to the Extended Memory Specification (XMS). The memory beyond the first 1 MB of address space is required by Windows 9x/Me in order to load, therefore these versions of Microsoft Windows required codice_1 to be loaded to be able to run.
codice_1 was first included with Windows 2.0 (1987), though it didn't support the full XMS specification.
As of MS-DOS 5.0 (1991), codice_1 could be used to load the DOS kernel code into the High Memory Area (HMA) to increase the amount of available conventional memory by specifying codice_4 in codice_5.
In DR DOS 5.0 (1990) and 6.0 (1991), the driver was named codice_6 rather than codice_1, like the corresponding codice_8 or codice_5 directive codice_10.
In FreeDOS, the matching file is named codice_11 and can be loaded from the FreeDOS configuration file named codice_12 or codice_5.
In Windows 3.1 and Windows 9x, there is also a command-line loadable version of HIMEM.SYS called XMSMMGR.EXE. It can load extended memory services after the system boots into the command prompt. This allows Windows Setup to load even if HIMEM.SYS is not loaded.