TAILIEUCHUNG - Lecture Computer organization and assembly language: Chapter 5 - Dr. Safdar Hussain Bouk
Lecture 05 - Memory Access. In this chapter, the following content will be discussed: Real Mode memory-addressing techniques, protected Mode memory-addressing techniques, 64-bit Flat Memory model, program-invisible registers in the 80286~Core2 microprocessors. | CSC 221 Computer Organization and Assembly Language Lecture 05: Memory Access Lecture 4: Review The programming model of the 8086 through 80286 contain 8- and 16-bit registers. The programming model of the 80386 and above contains 8-, 16-, and 32-bit extended registers as well as two additional 16-bit segment registers: FS and GS. Lecture 4: Review The 64-bit registers in a Pentium 4 with 64-bit extensions are RAX, RBX, RCX, RDX, RSP, RBP, RDI, RSI, and R8 through R15. In addition, the microprocessor contains an instruction pointer (IP/EIP/RIP) and flag register (FLAGS, EFLAGS, or RFLAGS). (cont.) Lecture Outline Memory Access: Real Mode memory-addressing techniques. Protected Mode memory-addressing techniques. Memory Access: 64-bit Flat Memory model. Program-invisible registers in the 80286~Core2 microprocessors. REAL MODE MEMORY ADDRESSING The only mode available on the 8086-8088. 20 bit address bus 1 MB, 16 bit data bus, 16 bit registers 80286 and above operate in either the real or protected mode. Real mode operation allows addressing of only the first 1M byte of memory space—even in Pentium 4 or Core2 microprocessor. the first 1M byte of memory is called the real memory, conventional memory, or DOS memory system 5 Segments and Offsets All real mode memory addresses must consist of a segment address plus an offset address. segment address defines the beginning address of any 64K-byte memory segment offset address selects any location within the 64K byte memory segment Figure in Next Slide: shows how the segment plus offset addressing scheme selects a memory location. 6 Figure: The real mode memory-addressing scheme, using a segment address plus an offset. this shows a memory segment beginning at 10000H, ending at location IFFFFH 64K bytes in length also shows how an offset address, called a displacement, of F000H selects location 1F000H in the memory Segments and Offsets 7 Figure: The real mode memory-addressing scheme, using a segment address plus an .
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