WIN386.EXE: Handles virtual memory and MS-DOS applications; converts extended to expanded memory if required.
KRNL386.EXE: Controls and allocates system resources, I/O and memory management, multitasking, and application launching.
USER.EXE: Controls input and output, including mouse, keyboard, sound, timer, and COM ports. Also provides the Windows user interface.
GDI.EXE: Manages display graphics and printing.
Core files: Windows loads dynamic-link libraries (DLLs) that provide the core Windows functionality. (As mentioned in Lesson 1, a DLL is a shareable library of executable code modules.)
System resources: Each DLL has a storage area in a 64-KB heap. If these heaps are full, you will receive "out of memory" error messages. Closing applications should relieve the problem.
Windows Device Drivers: As briefly mentioned, drivers are small programs that connect Windows to the hardware. This allows applications to be independent of devices. When a new piece of hardware is added to a system, this driver needs to be installed (it's usually provided on a floppy disk with the device). Information on device drivers is recorded in the SYSTEM.INI file.
Font Files: Windows provides three types of font files. Each font contains a complete character set for a particular typeface. Vector fonts are designed as a set of lines drawn between two points. Each character represents a mathematical model that can be scaled to virtually any size. Raster fonts are bitmap fonts made up of a set of dots. Each character or set of dots is "painted" on the screen or printer. Because each character requires separate data for each size, only limited scaling is possible. TrueType fonts are made from an "outline" of each character. When printing (on the screen or on a printer), these outlines are filled in. TrueType fonts are supported by all printers and provide WYSIWYG (What You See Is What You Get).
When loading, Windows uses the following files: