PC operating environments
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PC operating environmentsAlmost all x86-based PCs use the Windows operating systems. Windows 3.1 is rarely used today, but many 16-bit Windows 3.1 applications, as well as DOS applications, still run under Windows 98, XP and other 32-bit versions of Windows.
OS/2, highly regarded years ago as a robust operating system, had its loyal followers, but suffered from limited applications and support. However, OS/2 evolved into eComStation (see OS/2 and eComStation).
The Linux operating system, which is employed in millions of servers and embedded devices, is also used as an x86-based PC in lieu of Windows or Mac. However, Linux PCs are mostly used by technical professionals. See Linux.
The History of PC Operating Systems
The PC was created without a glimmer of its future potential, and as it became mainstream, its flaws surfaced. For example, the 8088 CPU was limited to one megabyte of memory, and the first 640K ("conventional memory") was used for applications. The remaining 384K "upper memory area" (UMA) was set aside for a screen buffer and other input/output (see PC memory map).
DOS was designed to run one application at a time, but users wanted to quickly switch between programs without having to close one and open the other. In order to solve this problem and the 640K memory limit, several remedies were created. Following is a synopsis.
In 1984, Borland introduced Sidekick and popularized the TSR "popup" program. Sidekick stayed in memory but was swapped in and out of view by pressing a hotkey. Users could instantly switch to a phone directory or notepad. However, keeping TSRs in memory did not leave room for big applications, and TSRs caused conflicts.
In 1984, expanded memory (EMS) was created to break the one megabyte barrier. An EMS board with RAM was plugged in, and its memory used directly by EMS applications. Lotus 1-2-3 quickly took advantage of EMS and hundreds of other applications were written to use it. See EMS.
Task Switchers and Multitaskers
Programs such as Software Carousel extended DOS's capabilities by allowing the user to keep a variety of programs open at the same time and switch back and forth between them. These "task switchers" used EMS memory, extended memory and/or the hard disk to swap applications in and out of conventional memory.
Combining multitasking with task switching, Quarterdeck's popular DESQview was the first control program to use expanded (EMS) memory to allow programs to run in, not just reside in, the background. See multitasking.
Memory managers were developed to store TSRs and other memory-resident software (drivers) in the upper memory area (UMA). Memory managers manage both extended and EMS memory, and products, such as QEMM, 386MAX and DOS 6's EMM386.EXE, allocated both types on demand. See DOS memory manager and memory allocation.
Extended Memory and Windows
By the late 1980s, the DOS extender was introduced, which was software that allowed DOS applications to not just reside in, but run in memory beyond one megabyte (extended memory). Paradox 386 and Lotus 1-2-3 were some of the first programs to use it.
Windows 3.0 managed all the memory in the PC and let users launch and switch between Windows and DOS applications. This advanced memory management contributed greatly to the success of Windows 3.0 and 3.1. Windows 95/98, which utilized the 32-bit architecture of the x86 chip, inherently used all of extended memory, but still dealt with conventional memory for legacy applications.
DOS 5 and 6
Since DOS was still the underlying OS with Windows 3.0 running on top, DOS was enhanced to interact with Windows effectively. DOS 6 allocated extended memory and EMS memory on demand, making it flexible for running a mix of old DOS and new Windows programs. See DOS 5 and DOS 6.
DR-DOS is a DOS-compatible operating system with advanced memory management and other features that always inspired Microsoft to include similar functionality in subsequent DOS releases. Novell acquired DR-DOS, added NetWare functionality and sold it to Caldera (see DR-DOS).
The Bad News
The legacy of TSRs, memory managers and task switchers combined with the various versions of DOS and Windows made quite a nightmare for the microcomputer manager before the mid-1990s.
The Good News
Starting with Windows 95, the memory problems were solved, and the memory management quagmire is but "a memory!" Now, people only have to deal with viruses, spam, identity theft and spyware!