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Unformatted text preview: d size override prefix. REX prefixes allow a 64-bit operand to be specified when operating in 64-bit mode. By using this mechanism, many existing instructions have been promoted to allow the use of 64-bit registers and 64-bit addresses. 3-2 Vol. 1 BASIC EXECUTION ENVIRONMENT 3.2 OVERVIEW OF THE BASIC EXECUTION ENVIRONMENT Any program or task running on an IA-32 processor is given a set of resources for executing instructions and for storing code, data, and state information. These resources (described briefly in the following paragraphs and shown in Figure 3-1) make up the basic execution environment for an IA-32 processor. An Intel 64 processor supports the basic execution environment of an IA-32 processor, and a similar environment under IA-32e mode that can execute 64-bit programs (64-bit sub-mode) and 32-bit programs (compatibility sub-mode). The basic execution environment is used jointly by the application programs and the operating system or executive running on the processor. Address space -- Any task or program running on an IA-32 processor can address a linear address space of up to 4 GBytes (232 bytes) and a physical address space of up to 64 GBytes (236 bytes). See Section 3.3.6, "Extended Physical Addressing in Protected Mode," for more information about addressing an address space greater than 4 GBytes. Basic program execution registers -- The eight general-purpose registers, the six segment registers, the EFLAGS register, and the EIP (instruction pointer) register comprise a basic execution environment in which to execute a set of general-purpose instructions. These instructions perform basic integer arithmetic on byte, word, and doubleword integers, handle program flow control, operate on bit and byte strings, and address memory. See Section 3.4, "Basic Program Execution Registers," for more information about these registers. x87 FPU registers -- The eight x87 FPU data registers, the x87 FPU control register, the status register, the x87 FPU instruction pointer register, the x87 FPU operand (data) pointer register, the x87 FPU tag register, and the x87 FPU opcode register provide an execution environment for operating on single-precision, double-precision, and double extended-precision floating-point values, word integers, doubleword integers, quadword integers, and binary coded decimal (BCD) values. See Section 8.1, "x87 FPU Execution Environment," for more information about these registers. MMX registers -- The eight MMX registers support execution of singleinstruction, multiple-data (SIMD) operations on 64-bit packed byte, word, and doubleword integers. See Section 9.2, "The MMX Technology Programming Environment," for more information about these registers. XMM registers -- The eight XMM data registers and the MXCSR register support execution of SIMD operations on 128-bit packed single-precision and doubleprecision floating-point values and on 128-bit packed byte, word, doubleword, and quad...
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- Winter '11