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

2. 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

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

4. 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

5. 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 (
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

6. 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

7. 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

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

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

10. 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