Such a design will enable manufacturers of computer systems using the microprocessor to advertise that the entire body of existing programs written for the prior microprocessor will run on their computer, thereby (in theory) stimulating computer sales to a point where software writers will begin to write programs designed to run in the new enhanced mode.
解答例
One such microprocessor is the Intel 80286, which is manufactured by the Intel Corporation of Santa Clara, Calif.
The design and operation of the Intel 80286 is described in detail in a publication entitled "iAPX 286 Programmer's Reference Manual Including the iAPX 286 Numeric Supplement," which is available from the Intel Corporation and is hereby incorporated by reference.
The Intel 80286 (hereinafter "80286") operates in two modes.
In a first mode, called the "real mode," the 80286 emulates the architecture of Intel's previous 8086, 8088 microprocessor family, which is used in the IBM PC and compatible computers, for example.
Thus, computers which incorporate the 80286 microprocessor, such as the IBM PC/AT, can run existing 8086 programs written for the IBM PC and compatible computers.
In a second mode, called the "protected mode," the 80286 architecture provides enlarged memory addressing capability, enhanced multi-tasking support features, and a sophisticated protection scheme.
Although the real mode will run existing 8086 programs, there are limitations associated with the real mode.
First, it limits the amount of physical memory which can be addressed to 1 megabyte. (In some computers, such as the IBM AT, the amount of physical memory available for programs has been further reduced to 640K.)
Second, the real mode does not provide memory relocation, a desirable feature for multi-tasking.
Third, the real mode provides no memory protection scheme, a feature needed for multi-tasking and network environments where user or task interference could be devastating.
Because of the limitations of the real mode, the 80286 was not designed to allow frequent switching from one mode to the other.
The 80286 is initialized in the real mode and can be switched to the protected mode by means of an instruction provided by the 80286.
No method or instruction is provided by the 80286 to switch from protected mode to real mode.
To return to real mode from protected mode, it is necessary to reset the microprocessor.
Thus, the designers of the 80286 contemplated that it would be used in one mode or the other, with real mode operation being kept separate from the protected mode operation, thereby isolating protected mode programs from the unprotected environment of the real mode.
Unfortunately, such isolation is undesirable from an efficiency standpoint.
For efficient operation, the operating system, or "DOS", of a microcomputer incorporating the 80286 should be able to run a mixture of real and protected mode programs in a multi-tasking environment.
It is an object of the present invention to provide improved methods of operating a multi-mode microprocessor that will enable a mixture of programs designed to run in the various modes of the microprocessor to be efficiently executed in a multi-tasking environment.
It is another object of the present invention to provide such methods that will, in alternate preferred embodiments, maximize the capabilities of the individual operating modes.
It is another object of the present invention to provide such methods that will only require the addition of minimal hardware to existing systems.
It is another object of this invention to provide an improved operating system for computers using multi-mode microprocessors.
It is another object of the present invention to provide, in alternate preferred embodiments, an improved system design for use with multi-mode microprocessors having a protected mode and an unprotected mode that will provide enhanced protection when operating in the unprotected mode.
It is another object of this invention to provide preferred embodiments of such methods which will enhance the multi-tasking capability of microprocessors such as the Intel 80286.
It is another object of the present invention to provide preferred methods designed for use with computers such as the IBM PC/AT which utilize the Intel 80286 which will optimize the operation of such computers in a multi-tasking, mode switching environment.
These and other objects of the invention, which will become more apparent as the invention is described more fully below, are obtained by providing an improved method of switching modes to execute a mixture of programs in a multi-mode microprocessor.
In preferred embodiments of the present invention designed for use with microprocessors which must be reset to switch from some modes to others, mode switching is preferably performed by activating the reset hardware in as efficient a manner as possible.
After the microprocessor is reset, improved boot-up software will determine whether the reset was triggered under software control (indicating a mode switching reset), in which case the normal initialization routines of the boot-up software are bypassed.
During reset procedures, special provisions are preferably made to handle direct memory access and interrupts.
Preferred embodiments of the present invention preferably include at least portions of the operating system, including device drivers and interrupt service routines, that can be executed in all modes.
