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	Protected mode - Wikipedia, the free encyclopedia
		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).
	en.wikipedia.org /wiki/Protected_mode (669 words)

	Real mode - Wikipedia, the free encyclopedia
		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).
	en.wikipedia.org /wiki/Real_Mode (302 words)

	MSN Encarta - Search Results - Real Mode
		Real Mode, in computer science, the native or default operating mode in IBM and other computers based on the Intel 80x86 family of microprocessors;...
		Mode (music), in music, term that varies in meaning from a scale to a scale-based formula for constructing melodies.
		Mode (mathematics), the number in a given set of numbers that appears most frequently.
	encarta.msn.com /Real_Mode.html (217 words)

	X86 assembly programming in real mode - Wikipedia, the free encyclopedia
		All modern x86 operating systems use protected mode; however, when the computer boots, it starts up in real mode, so the part of the operating system responsible for switching into protected mode must operate in the real mode environment.
		In real mode, two registers are used for a memory address: one to hold the segment, and one to hold the offset.
		This NASM-assembler program is an example of real mode code that prints "Hello world!" to the screen by means of writing directly to video.
	en.wikipedia.org /wiki/X86_assembly_programming_in_real_mode (1246 words)

	The Basics:What is Real Mode?
		To maintain backwards compatibility, the processor starts operating in real mode (using real mode addressing) but the processor state may be changed to a different mode (normally protected mode) using whatever the appropriate mechanism.
		System Management Mode Addressing is only available when running in system management mode, and that in turn is enabled by asserting a signal on the appropriate pin for the IA-32 CPU (assuming your version supports System Management Mode, of course).
		Real Mode is the execution mode of the IA-32 CPU when real mode addressing is being used.
	www.osronline.com /article.cfm?article=225 (424 words)

	kernel - real-time multitasking kernel, embedded realtime kernel
		Real mode is often attractive because it is simple and well understood.
		Performance of 16spm is somewhat slower than real mode or 32fpm, since hidden descriptor registers are loaded each time a segment register is changed.
		Moving to 16spm from real mode is especially easy, since the same Borland or Microsoft tools can be used to compile and link.
	www.smxinfo.com /articles/smx86ver.htm (1571 words)

	Function 0300 - Simulate Real Mode Interrupt (Site not responding. Last check: 2007-10-07)
		The target real mode handler must return with the stack in the same state as when it was called.
		This means that the real mode code may switch stacks while it is running, but must return on the same stack that it was called on and must return with an IRET.
		When this function returns, the real mode register data structure will contain the values that were returned by the real mode interrupt handler.
	www.tmt.com /helphtml/pmodew_func0300.htm (305 words)

	Using Real-Mode Callbacks (Site not responding. Last check: 2007-10-07)
		That is, a real mode program can use a real mode callback to pass information to the DPMI client, or obtain services provided by the DPMI client, without necessarily being aware of protected mode or extended memory in any way.
		The callback procedure is responsible for setting the proper address for resumption of real mode execution into the real mode register data structure; typically, this is accomplished by extracting the return address from the real mode stack and placing it into the CS:IP fields of the real mode register data structure.
		Since the real mode call structure and the selector used for the real mode SS are static, care must be taken when writing DPMI client callback procedures that may be reentered (for example, by a real mode program that services hardware interrupt).
	www.delorie.com /djgpp/doc/dpmi/ch4.6.html (979 words)

	PCTechGuide - The PC Technology Guide (Site not responding. Last check: 2007-10-07)
		"Real mode" refers to an operating mode of x86 chips that replicates the memory management used by 8086 or 8088 chips, characterised by an absence of memory management or memory protection features and limiting the processor to 1MB of memory.
		MS-DOS runs in real mode, and the phrase is often used to describe 16-bit MS-DOS device drivers.
		The real mode driver is the one identified as being a 16 bit DOS driver.
	www.pctechguide.com /tutorials/Win98Install_Real.htm (704 words)

	Function 0301 - Call Real Mode Procedure With Far Return Frame (Site not responding. Last check: 2007-10-07)
		The target real mode procedure must return with the stack in the same state as when it was called.
		This means that the real mode code may switch stacks while it is running, but must return on the same stack that it was called on and must return with a RETF and should not clear the stack of any parameters that were passed to it on the stack.
		When this function returns, the real mode register data structure will contain the values that were returned by the real mode procedure.
	www.tmt.com /helphtml/pmodew_func0301.htm (281 words)

	DPMI Specification
		Protected mode hardware interrupt handlers that need to call software running in real mode must either be sure that the real mode software that they are calling will not modify segment registers or they must use the state save service (see page 74) to save and restore the real mode segment registers.
		This means that the real mode code may switch stacks while it is running but it must return on the same stack that it was called on and it must pop off the entire far return/iret structure.
		Real mode call-backs can be used to hook real mode interrupts or to be called in protected mode by a real mode driver.
	burks.bton.ac.uk /burks/pcinfo/progdocs/dpmispec.htm (13846 words)

	Chapter 14 80386 Real-Address Mode (Site not responding. Last check: 2007-10-07)
		For full compatibility with 80286 real-address mode, pseudo-protection faults (interrupt 12 or 13 with no error code) occur if an effective address is generated outside the range 0 through 65535.
		Programs executing in real-address mode are able to take advantage of the new applications-oriented instructions added to the architecture by the introduction of the 80186/80188, 80286 and 80386: * New instructions introduced by 80186/80188 and 80286.
		Jump to the real mode code to be executed using a far JMP.
	library.n0i.net /hardware/intel80386/Chap14.html (2384 words)

	Chapter 2 - basic protected mode architecture
		Many drawbacks of real mode, most notably the fact that real mode programs can only access 1 MB of the computer's physical memory, motivated Intel to create a totally differant environment known as protected mode.
		Protected mode was introduced with the 80286 processor around 1990 (before the advent of the 80286 processor, computers ran exclusively in real mode).
		In protected mode, logical address are not converted to physical addresses by the shift-and-add method, as in real mode.
	www.geocities.com /efeiveson2003/ch2 (952 words)

	Segment Registers: Real mode vs. Protected mode (Site not responding. Last check: 2007-10-07)
		In real mode (or V86 mode), when you write any 16-bit value to a segment register, the value you write goes into the selector and 16 times that value goes into the base.
		In one version of my switch to flat real mode I had the selector value in a general register before switching to pmode, and the very first instruction after switching to pmode was a fast instruction to MOV that selector to a segment register.
		Flat real mode, AKA "unreal mode" is the mode you get to if you return to real mode from pmode leaving a 4GB limit in some or all of ds, es, fs, gs, ss.
	my.execpc.com /~geezer/johnfine/segments.htm (3387 words)

	15. Accessing 4 Gigs of Memory in Real Mode (Site not responding. Last check: 2007-10-07)
		In real mode, the value of the segment register is shifted left four bits to find the base address of the segment, and the size of the segment is always 64k.
		In protected mode, the value in the segment register is used as an index into a descriptor table located in memory, and the base address and size (which may be as small as 4 KB, or as large as 4 GB) from the descriptor table are loaded into the descriptor cache.
		After switching from protected mode to real mode, however, when you load the segment registers with their new values, the segment's base address is recalculated according to real mode rules, but the size limit is not changed.
	www.faqs.org /faqs/assembly-language/x86/general/part2/section-1.html (1119 words)

	ProtectedMode overview [deinmeister.de]
		Real Mode is the addressing mode in which the CPU behaves like being a 8086.
		In Real Mode, the memory was addressed by a segment register containing a start address and an index register which points to the address relatively to the address contained in the segment register.
		In Protected Mode index registers are used in the same way, but the role of the segment register has completely changed: It does no longer point to a physical address.
	www.deinmeister.de /x86modes.htm (1255 words)

	Virtual 8086 Mode (Site not responding. Last check: 2007-10-07)
		Firstly it was officially impossible to switch from protected back to real mode (although a clever IBM hack made this possible); secondly, protected mode was also incompatible with the vast amount of real-mode code around at the time.
		So V86 mode is very handy for this (and if you don't believe me, it's the same method used by SVGALib on Linux and various NT graphics drivers).
		We can see from this that V86 mode is more similar in some ways (address formation) to real mode, and in others (protection) to protected mode.
	www.openbg.net /sto/os/xml/v86.xml (2673 words)

	Real mode (Site not responding. Last check: 2007-10-07)
		The mode that allows an 80286, 80386, or 80486 processor to emulate an 8086 processor and run as though it were an 8086 processor.
		When running in protected mode, the 80286, 80386, and 80486 processors are capable of multitasking and addressing much more than 1 MB of memory.
		When running in real mode, these processors are subject to the same 1MB memory constraint as the 8086 processor, and they can run only one application or process at a time.
	www.novell.com /documentation/nw42/cncptenu/data/haw91lkm.html (139 words)

	Protected Mode tutorial
		In real mode, there is little to know about the segments.
		In protected mode, besides the segment base address, we also need the segment size (limit) and some flags indicating what the segment is used for.
		This is a fourth mode of operation found on the 386 CPU, with addressing similar to real mode but some of the protection mechanisms of protected mode.
	my.execpc.com /~geezer/os/pm.htm (1586 words)

	Computer with virtual machine mode and multiple protection rings (EP0187603B1)
		The two most privileged levels in the virtual mode are both treated as corresponding to the second most privileged level in the real mode, whereby if the processor is in the most privileged virtual operating mode, access to memory locations is permitted only if the location is accessible to the second most privileged mode.
		By means of the invention, at least two of the protection rings of the virtual mode are compressed, that is, they are made to correspond to a single protection ring used by the processor while processing in a real (non-virtual) mode.
		Otherwise stated, the most privileged ring of the processor operating in the virtual mode corresponds to a less than maximally privileged ring of the processor when it operates in the real mode, and two of the rings of the virtual mode correspond to one of the rings of the real mode.
	www.delphion.com /details?pn=EP00187603B1 (540 words)

	[No title] (Site not responding. Last check: 2007-10-07)
		If the SS:SP fields in the real mode register data structure are zero, a real mode stack will be provided by the DPMI host.
		The flags specified in the real mode register data structure will be pushed on the real mode stack's IRET frame.
		Note, however, that 16-bit hosts are not required to pass the high word of 32-bit general registers or the FS and GS segment registers to real mode even when running on an 80386 or later CPU.
	www.csse.monash.edu.au /~powell/pc_docs/dpmi/api/310300.html (352 words)

	real mode - Glossary - CNET.com (Site not responding. Last check: 2007-10-07)
		An operating mode of x86 chips that replicates the memory management used by 8086 or 8088 chips.
		Real mode limits the processor to 1MB of memory and provides no memory management or memory protection features.
		The phrase is often used to describe device drivers that operate in this mode.
	www.cnet.com /Resources/Info/Glossary/Terms/realmode.html (49 words)

	Real Mode
		What this means is that it has the advantage of speed, but it otherwise accesses memory with the same restrictions of the original 8088: a limit of 1 MB of addressable RAM, and slow memory access that doesn't take advantage of the full 32-bit processing of modern CPUs.
		Real mode is of course used by DOS and "standard" DOS applications.
		Note: The first 64 KB of extended memory is actually accessible to the PC in real mode, despite the fact that it is not supposed to be possible.
	www.pcguide.com /ref/cpu/arch/int/modesReal-c.html (394 words)

	Protected Mode Basics (Site not responding. Last check: 2007-10-07)
		In real mode, memory segmentation is handled automatically through the use of an internal mechanism, in conjunction with segment registers.
		At power-up, the descriptor cache registers are loaded with fixed, default values, the CPU is in real mode, and all segments are marked as read/write data segments, including the code segment (CS).
		All that remains in order to enter protected mode is changing the CPU state to protected mode and jumping to clear the prefetch queue (not necessary on the Pentium).
	x86.ddj.com /articles/pmbasics/tspec_a1_doc.htm (4153 words)

	kernel - real-time multitasking kernel, embedded realtime kernel, x86, real mode, protected mode
		This version provides an easy step into protected mode from real mode; little change is required to the application code, since it is still 16-bit C/C++ code.
		One smx library is provided for each of the four memory models (which are the same as for real mode.) As in real mode, the processor 3 switch can be used for better performance and reduced code size on a 386-class processor.
		The Real Mode EXE Bootloader is capable of loading and executing a real-mode, EXE file from boot, without DOS present.
	www.smxinfo.com /rtos/kernel/smx86.htm (2269 words)

	The Old Joel on Software Forum - Calling real mode FAR call from protected mode
		There is call _go32_dpmi_simulate_fcall which helps to execute real mode FAR calls from protected mode.
		If you set up say 64 paragraphs (1K) of conventional memory to be used as your real-mode call stack and pass that in as SS:SP of the DPMI real mode call structure.
		However by moving the parameter data to the real mode memory and set SP accordingly, you should get a usable stack frame.
	discuss.fogcreek.com /joelonsoftware?cmd=show&ixPost=131513 (353 words)

	DPMI: 11.4 Allocate Real Mode Call-Back Address (Site not responding. Last check: 2007-10-07)
		At times it is necessary to hook a real mode interrupt or device call-back in a protected mode driver.
		Since the real mode call structure is static, you must be careful when writing code that may be reentered.
		If the real mode CS:IP is left unchanged then the real mode call-back will be executed immediately and your procedure will be called again.
	www.tenberry.com /dpmi/1104.html (740 words)

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