The University of Adelaide, School of Computer Science 24 February 2019 Lecture 2.1 Instructions: Introduction Chapter 2 — Instructions: Language of the Computer

Morgan Kaufmann Publishers 24 February, 2019 Objectives Understand that the instruction set is the repertoire of instructions of a computer Remember that the memory is always addressed at the unit of byte Memory only accepts byte addresses Convert between byte address and word address Tell the difference between big-endian computer and little-endian computer Underline two key principles of machine design Chapter 2 — Instructions: Language of the Computer — 2 Chapter 4 — The Processor

Coverage Textbook Chapters 2.1, 2.2, 2.3 Chapter 2 — Instructions: Language of the Computer — 3

The University of Adelaide, School of Computer Science 24 February 2019 Instruction Set §2.1 Introduction The repertoire of instructions of a computer Different computers have different instruction sets But with many aspects in common Early computers had very simple instruction sets Simplified implementation Many modern computers also have simple instruction sets Chapter 2 — Instructions: Language of the Computer — 4 Chapter 2 — Instructions: Language of the Computer

The MIPS Instruction Set The University of Adelaide, School of Computer Science 24 February 2019 The MIPS Instruction Set Used as the example throughout the book 32-bit Computer, i.e., MIPS-32 Stanford MIPS commercialized by MIPS Technologies (www.mips.com) Large share of embedded core market Applications in consumer electronics, network/storage equipment, cameras, printers, … One example of RISC instruction sets Typical of many modern instruction set architectures (ISAs) See MIPS Reference Data tear-out card, and Appendixes A and E Chapter 2 — Instructions: Language of the Computer — 5 Chapter 2 — Instructions: Language of the Computer

Representation of Memory Addresses The University of Adelaide, School of Computer Science 24 February 2019 Representation of Memory Addresses Memory addresses are given in the unit of byte Show an example of an array of 10 words, say array Ax. Say the address of Ax[0] is 120, ask the address of Ax[1], Ax[2], … Chapter 2 — Instructions: Language of the Computer — 6 Chapter 2 — Instructions: Language of the Computer

The University of Adelaide, School of Computer Science 24 February 2019 Save Words A multiple-byte word is stored in multiple consecutive bytes The address of a word matches the address of one of the multiple bytes within the word Use the smallest address in general In MIPS, words must start at addresses of multiples of 4 Show an example of an array of 10 words, say array Ax. Say the address of Ax[0] is 120, ask the address of Ax[1], Ax[2], … Chapter 2 — Instructions: Language of the Computer — 7 Chapter 2 — Instructions: Language of the Computer

Word Address for Convenience Word address = Byte address ÷ 4 Chapter 2 — Instructions: Language of the Computer — 8

Store words into memory Chapter 2 — Instructions: Language of the Computer — 9

Two Key Principles of Machine Design Instructions are represented as numbers and, as such, are indistinguishable from data Programs are stored in alterable memory (that can be read or written to) just like data Stored-program concept Programs can be shipped as files of binary numbers Computers can inherit ready-made software provided they are compatible with an existing ISA – leads industry to align around a small number of ISAs Chapter 2 — Instructions: Language of the Computer — 10