Intel® Extended Memory 64 Technology Software Developer's Guide

prefixes are treated as a legacy IA-32 instruction). Compatibility mode uses 16-bit and 32-bit address and operandsizes. Like legacy protected mode, this mode allows applications to access up to 64GB of physical memory using PAE(Physical Address Extensions).The following elements of legacy protected mode are not supported while in compatibility mode:• Virtual 8086 mode, task switches and stack parameter copy features• From the operating system’s viewpoint: system data structures, address translation, interrupt and exceptionhandling; use 64-bit mechanisms instead of 32-bit mechanisms to handle these structures or events1.2.4. Legacy ModesLegacy mode includes protected mode, real address mode, and virtual 8086 mode. Software written for these modesis fully compatible with processors supporting Intel EM64T.1.2.5. System Management ModeSystem management mode (SMM) in a processor supporting Intel EM64T provides the same execution environmentfor the system management interrupt (SMI) handler as was provided in the legacy IA-32 environment. Upon thedelivery of an SMI, the processor switches to SMM and saves the processor state according to the SMRAM state savemap.SMM supports transitions from/to other operating modes (IA-32e and legacy modes). An SMI handler can access anyphysical memory pages using the PSE mechanism. The SMM environment does not support 64-bit linear addressbecause PAE is not supported.Vol. 1 1-3