Modern Processor Architectures and Instruction Sets

Most modern personal computers contain a processor supporting either the Intel or AMD version of the x86 32-bit and x64 64-bit architectures. In contrast, almost all smartphones, smartwatches, tablets, and many embedded systems contain ARM 32-bit or 64-bit processors. This chapter takes a detailed look at the registers and instruction sets of these processor families.

After completing this chapter, you will understand the high-level architectures and unique attributes of the x86, x64, 32-bit ARM, and 64-bit ARM registers, instruction sets, assembly languages, and key aspects of legacy features supported in these architectures.

This chapter covers the following topics:

• x86 architecture and instruction set
• x64 architecture and instruction set
• 32-bit ARM architecture and instruction set
• 64-bit ARM architecture and instruction set

Technical requirements

The files for this chapter, including the answers to the exercises, are available at https://github.com/PacktPublishing/Modern-Computer-Architecture-and-Organization-Second-Edition.

x86 architecture and instruction set

For the purposes of this discussion, the term x86 refers to the 16-bit and 32-bit instruction set architecture of the series of processors that began with the Intel 8086, introduced in 1978. The 8088, released in 1979, is functionally very similar to the 8086, except it has an 8-bit data bus instead of the 16-bit bus of the 8086. The 8088 was the central processor in the original IBM PC.

Subsequent generations of this processor series were named 80186, 80286, 80386, and 80486, leading to the term “x86” as shorthand for members of the family. Subsequent generations dropped the numeric naming convention and received the names Pentium, Core, i Series, Celeron, and Xeon.

Advanced Micro Devices (AMD), a semiconductor manufacturing company that competes with Intel, has been producing x86-compatible processors since 1982. Some recent AMD x86 processor generations have been named Ryzen, Opteron, Athlon, Turion, Phenom, and Sempron...

x64 architecture and instruction set

The original specification for a processor architecture extending the x86 processor and instruction set to 64 bits, named AMD64, was introduced by AMD in 2000. The first AMD64 processor, the Opteron, was released in 2003. Intel found itself following AMD’s lead and developed an AMD64-compatible architecture, eventually given the name Intel 64. The first Intel processor that implemented the 64-bit architecture was the Xeon, introduced in 2004. The name of the architecture shared by AMD and Intel came to be called x86-64, reflecting the evolution of x86 to 64 bits, and, in popular usage, this term has been shortened to x64.

The first Linux version supporting the x64 architecture was released in 2001, well before the first x64 processors were even available. Windows began supporting the x64 architecture in 2005.

Processors implementing the AMD64 and Intel 64 architectures are largely compatible at the instruction set level of user-mode...

32-bit ARM architecture and instruction set

The ARM architectures define a family of RISC processors suitable for use in a wide variety of applications. Processors based on ARM architectures are preferred in designs where a combination of high performance, low power consumption, and small physical size is needed.

ARM Holdings, a British semiconductor and software company, developed the ARM architectures and licenses them to other companies who implement processors in silicon. Many applications of the ARM architectures are system-on-chip (SoC) designs combining a processor with specialized hardware to support functions such as cellular radio communications in smartphones.

ARM processors are employed in a broad spectrum of applications, from tiny battery-powered devices to supercomputers. ARM processors serve as embedded processors in safety-critical systems such as automotive anti-lock brakes and as general-purpose processors in smartwatches, portable phones, tablets, laptop...

64-bit ARM architecture and instruction set

The 64-bit version of the ARM architecture, named AArch64, was announced in 2011. This architecture has 31 general-purpose 64-bit registers, 64-bit addressing, a 48-bit virtual address space, and a new instruction set named A64.

The 64-bit instruction set is a superset of the 32-bit instruction set, allowing existing 32-bit code to run unmodified on 64-bit processors.

Instructions are 32 bits wide, and most operands are 32 or 64 bits. The A64 register functions differ in some respects from 32-bit mode: the program counter is no longer directly accessible as a register and an additional register is provided that always returns an operand value of zero.

At the user privilege level, most A64 instructions have the same mnemonics as the corresponding 32-bit instructions. The assembler determines whether an instruction operates on 64-bit or 32-bit data based on the operands provided. The following rules determine the operand length...

Summary

Having completed this chapter, you should have a good understanding of the high-level architectures and features of the x86, x64, 32-bit ARM, and 64-bit ARM registers, instruction sets, and assembly languages.

The x86 and x64 architectures represent a mostly CISC approach to processor design, using variable-length instructions that can take many cycles to execute, a lengthy pipeline, and (in x86) a limited number of processor registers.

The ARM architectures, on the other hand, implement RISC processors with mostly single-cycle instruction execution, a large register set, and (somewhat) fixed-length instructions. Early versions of ARM had pipelines as short as three stages, though later generations have considerably more stages.

Is one of these architectures better than the other, in a general sense? It may be that each is better in some ways, and system designers must make their selection of processor architecture based on the specific needs of the system under...

Exercises

1. Install the free Visual Studio Community edition, available at https://visualstudio.microsoft.com/vs/community/, on a Windows PC. Once installation is complete, open the Visual Studio IDE and select Get Tools and Features… under the Tools menu. Install the Desktop development with C++ workload.

   In the Windows search box in the Task bar, begin typing Developer Command Prompt for VS 2022. When the app appears in the search menu, select it to open Command Prompt.

   Create a file named hello_x86.asm with the content shown in the source listing in the x86 assembly language section of this chapter.

   Build the program using the command shown in the x86 assembly language section of this chapter and run it. Verify that the output Hello, Computer Architect! appears on the screen.

2. Write an x86 assembly language program that computes the following expression and prints the result as a hexadecimal number: [(129 – 66) × (445 + 136)] ...