The file HIMEM.sys (found in the system32 folder) acts as an extended memory manager. It coordinates the use of computer's extended memory including the high memory area (HMA) so that no two applications or device drivers use the same memory at the same time. In Windows 95/98, HIMEM.sys is automatically loaded at startup. To free up more conventional memory, HIMEM.sys also allows part of DOS to be loaded into the first 64K block of extended memory known as the high memory area (HMA).
On a Config.sys file HIMEM.sys is first on the device list. This is to avoid any conflict with other devices, which use EISA (Extended Industry Standard Architecture) memory. EISA is bus standard for IBM compatibles that extends the ISA bus architecture to 32 bits and allows more than one CPU to share the bus.
If the Config.sys file is corrupted or if the file does not have the path to the Himem.sys file or a wrong version of Himen.sys is loaded, an error "Himem.sys not loaded" will be generated.
This error was seen mostly in Windows 3.0 & in Windows 95. The error would most likely occur when the system is restarted from DOS to Windows.
