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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 10.3</TITLE></HEAD><BODY><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="s10_02.htm">10.2 Software Initialization for Real-Address Mode</A><BR><B>next:</B> <A HREF="s10_04.htm">10.4 Software Initialization for Protected Mode</A><P><HR><P><H1>10.3 Switching to Protected Mode</H1>Setting the PE bit of the MSW in CR0 causes the 80386 to begin executing inprotected mode. The current privilege level (CPL) starts at zero. Thesegment registers continue to point to the same linear addresses as in realaddress mode (in real address mode, linear addresses are the same physicaladdresses).<P>Immediately after setting the PE flag, the initialization code must flushthe processor's instruction prefetch queue by executing a <A HREF="JMP.htm">JMP</A> instruction.The 80386 fetches and decodes instructions and addresses before they areused; however, after a change into protected mode, the prefetchedinstruction information (which pertains to real-address mode) is no longervalid. A <A HREF="JMP.htm">JMP</A> forces the processor to discard the invalid information.<P><HR><P><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="s10_02.htm">10.2 Software Initialization for Real-Address Mode</A><BR><B>next:</B> <A HREF="s10_04.htm">10.4 Software Initialization for Protected Mode</A></BODY>⌨️ 快捷键说明
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