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CAN 8086 work in protected mode?
Most 8086 application programs can be re-compiled or re-assembled and executed on the 80286 in Protected Mode. For the most part, the binary compatibility with real-mode code, the ability to access up to 16 MB of physical memory, and 1 GB of virtual memory, were the most apparent changes to application programmers.
How do I know I am in protected mode?
Once you’ve stored the MSW in some register, you can AND that register with 1 to zero out all but the last bit on the register. Then, CMP the register to find out what it is; if it’s 1, you know the CPU is in protected mode. If it’s 0, you know the CPU is in real mode.
What is CPU real mode?
Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode provides no support for memory protection, multitasking, or code privilege levels.
When was protected mode released on the 286?
The initial protected mode, released with the 286, was not widely used; for example, it was used by Coherent (from 1982), Microsoft Xenix (around 1984) and Minix. Several shortcomings such as the inability to access the BIOS or DOS calls due to inability to switch back to real mode without resetting the processor prevented widespread usage.
How to switch from protected to real mode?
It’s pretty well documented how to get the 286 from real mode to its 16-bit protected mode. It’s also widely stated that the 286 had no officially supported way of going back from protected mode into real modewithout losing its current state. The “obvious” way to do it was pretty much a no-op.
What does protected mode do on the Intel 386?
With the release of the 386, protected mode offers what the Intel manuals call virtual 8086 mode. Virtual 8086 mode is designed to allow code previously written for the 8086 to run unmodified and concurrently with other tasks, without compromising security or system stability.
Is there physical address space in protected mode?
32-bit physical and virtual address space (The 32-bit physical address space is not present on the 80386SX, and other 386 processor variants which use the older 286 bus.) Until the release of the 386, protected mode did not offer a direct method to switch back into real mode once protected mode was entered.