Hardware, software and device technology build a single unit in a plant. If nothing is changed, nothing happens.

In further developments of an operating system, an existing technology is mostly not (weiter-) developed anymore, but is still supported by the operating system.

Up to now Microsoft has never dropped the history and has always provided an upward compatibility.

DOS-Software is still running up to now in the DOS-Box, if it is engineered “clean” on BIOS (Basic Input/output System) interfaces.

DOS-Software which works with BIOS interrupt-calls are able to access file formats, which even have not been known at time of development. Norton Commander is able to access NTFS file format.

WORD 3.0 documents can still be opened in Windows XP.

Microsoft has mostly pursued a migration strategy.

A migration strategy has been provided for e.g. document formats (Word) or file formats (FAT32/NTFS). Conversion programs are available for the transformation.

Microsoft has always created upward compatibility for internal interface technologies (e.g. DDE, OLE, COM).