TopView was a text-mode MS-DOS multitasker written by IBM and released in 1985. In order to compete with various other graphical environments, IBM announced TopView before it was finished, around the time they shipped their new PC AT computer (in 1984).
IBM considered that in order to harness the great power and memory capacity of the new machine (Intel 80286 with a 6MHz clock and, in version 02, with 512KB of RAM), some multitasking environment was necessary. TopView allowed IBM to sweeten the deal with customers, who were surprised that the new and very expensive machine did not come with an operating system able to use the hardwar] multitasking and protected-mode features of the new CPU, and was still running in 8088 emulation mode. However, TopView proved unnecessary to sell the new machines, and was quickly dropped.
TopView ran in real mode on any x86 processor and could run well-behaved MS-DOS programs in windows. It did not make use of any later introduced virtualization features in the Intel 80386 processors.
TopView first introduced PIF files, which defined how a given MS-DOS program should be run in a multi-tasking environment, notably to avoid giving it unnecessary resources which could remain available to other programs. TopView's PIF files were inherited and extended by DESQview and Microsoft Windows.
TopView required MS-DOS 2.x and did not run with 3.0 and later releases.
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