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THE INTEL 80x86 Microprocessor

THE INTEL 80x86 Microprocessor. The world’s most popular architecture. OVERVIEW. MIPS was the version of a single small group in 1985; the pieces of this architecture fit nicely together, and the whole architecture can be described succinctly

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THE INTEL 80x86 Microprocessor

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  1. THE INTEL 80x86 Microprocessor The world’s most popular architecture

  2. OVERVIEW • MIPS was the version of a single small group in 1985; the pieces of this architecture fit nicely together, and the whole architecture can be described succinctly • The 80x86 is the product of several independent groups who evolved the architecture over almost 20 years, adding new features to the original instruction set.

  3. HISTORY • 1978: The Intel 8086 architecture was announced as an assembly-language-compatible extension of the Intel 8080. The Intel 80x86 is a 16-bit architecture with all internal registers 16 bits wide. • 1980: The Intel 8087 floating-point coprocessor is announced, which extends the 8086 with about 60 floating point instructions. Instead of using registers, it relies on a stack. • 1982: The 80286 extended the 8086 architecture by increasing the address space to 24 bits.

  4. HISTORY ( cont.) • 1885: The 80386 extended the 80286 architecture to 32 bits. The added instructions make the 80386 nearly a general-purpose register machine. • 1989-95: The subsequent 80486 in 1989, Pentium in 1992, and the Pentium Pro in 1995 were aimed at higher performance, with only four instructions added to the user-visible instruction set • 1997: Intel announced that it would expand the Pentium and the Pentium Pro architecture with MMX. This new set of 57 instructions uses the floating-point stack to accelerate multimedia and communication applications.

  5. REGISTERS AND DATA ADDRESSING • The evolution of the instruction set can be seen in the registers of the 80386. • The 80386 extended all 16-bit registers to 32 bits. • The 80386 contains only eight GPRs (general-purpose registers) which means that MIPS programs can use four times as many. • The arithmetic logical and data transfer instructions are two-operand instructions that allow the following combinations.

  6. 80386 REGISTER SET

  7. 8086 vs MIPS • There are two important differences • The 8086 arithmetic and logical instructions must have one operand act as both a source and a destination; MIPS allows separate registers for source and destination. • The second important difference is that one of the operands can be in memory. Thus virtually any instruction may have one operand in memory, unlike MIPS and PowerPC.

  8. 8086 INTEGER OPERATIONS • The 8086 provides support for both 8-bit and 16-bit data types. • The 80386 adds 32-bit addresses and data in the 8086 • The 80386 architects provide a convenient way to specify each version without expanding code size significantly. • Since most programs are dominated by 16 or 32-bits, a default large size was created, which is set by a bit in the code segment register.

  9. INTEGER OPERATION’S 4 MAJOR CLASSES • Data movement instructions, including move, push, and pop • Arithmetic and logical instructions, including test, integer, and decimal arithmetic operations • Control flow, including conditional branches, unconditional jumps, calls, and returns • String instructions, including string move and string compare

  10. TYPICAL 80x86 INSTRUCTIONS AND FUNCTIONS

  11. TYPICAL 80x86 INSTRUCTION FORMATS

  12. CONDITIONAL BRANCH • Conditional branches are based on conditional codes or flags • Condition codes are set as as a side effect of an operation; most are used to compare the values of a result to 0. Branches then test the condition. • The argument for condition codes is that they occur as part of normal operations and are faster to test than it is compare registers as MIPS does for beq and bne.

  13. STRING INSTRUCTIONS • String instructions are part of the 8086 ancestry of the 8086 and are not commonly executed in most programs. • They are often slower than equivalent software routines.

  14. 8086 INSTRUCTION ENCODING • Encoding of instructions in the 8086 is complex, with many different instruction formats. • Instructions for the 80386 may vary from 1 byte, when there are no operands, up to 17 bytes. • The opcode byte usually contains a bit saying whether the operand is 8 bits or 32 bits • For some instructions, the opcode may include the addressing mode and the register. • Other instructions use a “postbyte” or extra opcode byte, which contains the addressing mode information.

  15. CONCLUSION • Intel had a processor 2 years before its competitors such as the Motorola 68000 • The 68000 was a more elegant design • This head start led IBM to select the 80x86 as the CPU for the IBM PC • Intel agrees that the architecture is more difficult to build than machines like MIPS

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