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Encyclopedia > Real mode

Real mode (also called real address mode in Intel's manuals) is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space (meaning that only 1 MB of memory can be addressed), direct software access to BIOS routines and peripheral hardware, and no concept of memory protection or multitasking at the hardware level. All x86 CPUs in the 80286 series and later start up in real mode at power-on; 80186 CPUs and earlier had only one operational mode, which is equivalent to real mode in later chips. The Intel 80286 is an x86-family 16-bit microprocessor that was introduced by Intel on February 1, 1982. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Intel 80486DX2 microprocessor in a ceramic PGA package A central processing unit (CPU), or sometimes simply processor, is the component in a digital computer that interprets instructions and processes data contained in software. ... MB may mean: MegaByte or Megabit Bachelor of Medicine, an academic degree (Latin Medicinae Baccleureus) Honda MB, a Honda 50 cc motorcycle from the early 1980s Manitoba, Canada: postal code Manned Base, in military parlance Marching Band, a group of people that play instruments while marching in unison to form... This article is about the software. ... Memory protection is a system that prevents one process from corrupting the memory of another process running on the same computer at the same time. ... In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is... The Intel 80286 is an x86-family 16-bit microprocessor that was introduced by Intel on February 1, 1982. ... The 80186 is a microprocessor that was developed by Intel circa 1982. ...


The 286 architecture introduced protected mode, allowing for (among other things) hardware-level memory protection. Using these new features, however, required extra software instructions not previously necessary. Since a primary design specification of x86 microprocessors is that they be fully backwards compatible with software written for all x86 chips before them, the 286 chip was made to start up in 'real mode' — that is, in a mode which turned off the new memory protection features, so that it could run software written for older microprocessors. To this day, even the newest x86 CPUs start up in real mode at power-on, and can run software written for any previous chip. Protected mode is an operational mode of x86-compatible CPUs of the 80286 series or later. ...


The DOS operating systems (MS-DOS, DR-DOS, etc.) operate in real mode. Early versions of Microsoft Windows (which were essentially just graphical user interface shells running on top of DOS, and not actually operating systems per se) ran in real mode, until Windows 3.0, which could run in either real or protected mode. Windows 3.0 could actually run in two "flavours" of protected mode - "standard mode", which ran using protected mode, and "386-enhanced mode", which also used 32 bit addressing and thus would not run on a 286 (despite having protected mode, the 286 was still a 16 bit chip; 32 bit registers were introduced in the 80386 series). Windows 3.1 removed support for Real Mode, and was the first mainstream operating environment which required at least an 80286 processor (not counting Windows 2.0 which was not a mainstream product). Almost all modern x86 operating systems (Linux, Windows 95 and later, OS/2, etc.) switch the CPU into protected mode at startup. It has been suggested that X86 DOS Comparison be merged into this article or section. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... DR-DOS is a DOS-family-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildalls Digital Research and derived from CP/M-86. ... Windows redirects here. ... A graphical user interface (or GUI, sometimes pronounced gooey) is a method of interacting with a computer through a metaphor of direct manipulation of graphical images and widgets in addition to text. ... A typical Windows 3. ... The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ... Windows 2. ... Tux the penguin, based on an image created by Larry Ewing in 1996, is the logo and mascot of Linux. ... Windows 95 (codename Chicago) is a hybrid 16-bit/32-bit graphical user interface-based operating system released on August 24, 1995 by the Microsoft Corporation. ... OS/2 was an operating system created by Microsoft and IBM and later developed by IBM exclusively. ...


See also


  Results from FactBites:
 
Protected mode - Wikipedia, the free encyclopedia (669 words)
The other operational mode of 286 and later CPUs is real mode, a backwards compatibility mode that disables these features, designed to allow old software to run on newer chips.
While software-mediated multitasking is certainly possible on systems running in real mode, the memory protection features of protected mode prevent an erroneous program from damaging the memory "owned" by another task or by the operating system kernel.
Contributing to the confusion, the protected mode and virtual 8086 mode enhancements in Windows/386 and later were called 386 enhanced mode because they required a 386 and later (thus its name) in addition to protected mode, and would not run on a 286 (even though 286es support protected mode).
Real mode - Wikipedia, the free encyclopedia (302 words)
Real mode (also called real address mode in Intel's manuals) is an operating mode of 80286 and later x86-compatible CPUs.
Real mode is characterized by a 20 bit segmented memory address space (meaning that only 1 MB of memory can be addressed), direct software access to BIOS routines and peripheral hardware, and no concept of memory protection or multitasking at the hardware level.
Windows 3.1 removed support for Real Mode, and was the first mainstream operating environment which required at least an 80286 processor (not counting Windows 2.0 which was not a mainstream product).
  More results at FactBites »

 
 

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