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TopView is a text-mode PC DOS multitasking, object-oriented windowing environment written by IBM, announced in August 1984〔IBM. ''TopView Announcement Letter''. 1984-08-14 (()).〕 and shipped in March 1985.〔IBM. ''TopView Announcement Letter''. 1985-02-19 (()).〕 TopView provided an operating environment that allowed users to run more than one application at the same time on a PC. Many industry leaders and insiders speculated on what was happening in the confidential confines of IBM Boca Raton. IBM demonstrated an early version of the product to key customers before making it generally available, around the time they shipped their new PC AT computer. == Hopeful beginnings == When Microsoft announced Windows in November 1983, International Business Machines (IBM), Microsoft's important partner in popularizing MS-DOS for the IBM PC, notably did not announce support for the forthcoming window environment. IBM determined that the microcomputer market needed a multitasking environment. When it released TopView in 1985, the press speculated that the software was the start of IBM's plan to increase its control over the IBM PC (even though nothing about the IBM PC was proprietary (including the BIOS which was published to the world)) by creating a proprietary operating system for it, similar to what IBM had offered for years on its larger computers. TopView also allowed IBM to serve customers who were surprised that the new IBM AT did not come with an operating system able to use the hardware multitasking and protected mode features of the new 80286 CPU, as DOS and most applications were still running in 8086/8088 real mode. Even given TopView's virtual memory management capabilities, hardware limitations still held the new environment back—a base AT with 256 KB of RAM only had room for 80 KB of application code and data in RAM once DOS and TopView had loaded up. 512-640 KB was recommended to load up two typical application programs of the time. This was the maximum the earlier IBM XT could have installed. Once loaded, TopView took back much of the memory consumed by DOS, but still not enough to satisfy industry critics. TopView ran in real mode on any x86 processor and could run well behaved DOS programs (i.e. programs that did not write directly to the screen but used BIOS int 10h and DOS int 21h (such as the IBM Assistant Series of productivity programs)) in an arrangement of windows. Well behaved applications would use standard DOS and BIOS function calls to access system services and hardware. Misbehaving programs (i.e. such as programs that did write directly to the screen) such as Lotus 1-2-3, WordStar and dBase III would still run in the TopView environment, however, they would consume the entire screen.〔 Object-oriented applications were written using the TopView API. TopView was not updated to make use of the virtual 8086 mode added in the Intel 80386 processors that allowed better virtualization. Initially, compatibility with the extended features was limited mainly to IBM applications, along with a few third-party products like WordPerfect and VolksWriter. A chicken-and-egg situation developed where third-party developers were reluctant to add extended feature support (such as block insert and delete to allow users to do cut/copy/paste between applications) when they did not see market demand for them.〔 Most DOS programs did, however, support these functions and did allow the user to perform the cut, copy, and paste operations by using the TopView pop-up menus. Some believed that IBM planned to use TopView to force them to rely on them to comply with the new technical specifications.〔 As later versions of TopView were released, it was able to successfully make more challenging DOS apps run in a multitasking fashion by intercepting direct access to system services and hardware. TopView first introduced Program Information Files (PIF files), which defined how a given 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 Quarterdeck's DESQview and Microsoft Windows.〔(Dobb's Undocumented Corner- The PIF File Format, or, TopView (sort of) Lives! )〕 The concept of Program Information Files was also used under Digital Research operating systems such as Concurrent DOS, Multiuser DOS, System Manager and REAL/32, however, using the PIFED command, the necessary program information got directly embedded into the .EXE or .COM executable file.〔Digital Research. ''Concurrent DOS 386 - Multiuser/Multitasking Operating System - Reference Manual''. 1987 (()).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IBM TopView」の詳細全文を読む スポンサード リンク
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