CEN 226: Computer Organization & Assembly Language :CSC 225 (Lec#1) By Dr. Syed Noman

Course organization Course is divided into two sections: ▫Computer organization ▫Assembly language programming Computer organization and assembly language are interrelated. ▫Program in assembly and get better understanding of the machine ▫Get familiarized with the machine to better program in assembly language. To program in assembly language requires knowledge of the machine.

Text Book

Reference Book 4

Course Outline Introduction to PC hardware. von Neumann machine 8086 machine architecture PC software requirements Assembly language programmers requirements Program logical and control String operations Arithmetic operations for processing binary data Assembling linking and executing a program.

Marks Distribution Lab : 20 Marks Mid-1: 15 Marks Mid-2: 15 Marks Assignment: 6 marks Quizzes: 2 Marks (best of 2 out of 3) Attendance: 2 Marks (after 2 absents, 1 mark will be deducted) Final: 40 Marks

Collection of Programs Learning Tip: object of the program must be clearly defined. Program Codes are as follows: ▫EP#: Example program number ▫LT#: Lab Task number ▫QP#: Quiz program number ▫AP#: Assignment program#

8 Software Hierarchy Levels LevelDescription Application Program Software designed for a particular class of applications High-Level Language (HLL) Programs are compiled into either assembly language or machine language. E.g. C++, Pascal, Java, Visual Basic, etc. Operating Systems Contains procedures than can be called from programs written in either high-level language or assembly language. This system may also contain an application programming interface (API). Assembly Language (ASM) Uses instruction mnemonics that have a one-to-one correspondence with machine language. Machine Language (ML) Numeric instructions and operands that can be stored in memory and directly executed by the computer processor.

9 What is Assembly Language? A low-level processor- specific programming language, designed to match the processor’s machine instruction set each assembly language instruction matches exactly one machine language instruction we study here Intel’s 80x86 (and Pentiums)

10 Why learn Assembly Language? To learn how high-level language code gets translated into machine language ▫i.e.: to learn the details hidden in HLL code To learn the computer’s hardware ▫by direct access to memory, video controller, sound card, keyboard… To speed up applications ▫direct access to hardware (ex: writing directly to I/O ports instead of doing a system call) ▫good ASM code is faster and smaller: rewrite in ASM the critical areas of code

11 Table: Comparison of Assembly Language and High-Level Languages Type of ApplicationsHigh-Level LanguageAssembly Language Business application software for single platform. Formal structures make it easy to organize and maintain. No formal structure. Hardware device driver. Awkward coding techniques required. Hardware access is straightforward and simple. Business application for multiple platforms. Portable.Difficult to maintain. Embedded systems and computer games requiring direct hardware access. Produces too much executable code, and may not run efficiently. Ideal, because the executable code is small and runs quickly.

12 Machine Language An assembler is a program that converts ASM code into machine language code: ▫ mov al,5 (Assembly Language) ▫ (Machine Language)  most significant byte is the opcode for “move into register AL”  the least significant byte is for the operand “5” Directly programming in machine language offers no advantage (over Assembly)...

13 Binary Numbers/Storage Size are used to store both code and data On Intel’s x86: ▫byte = 8 bits (smallest addressable unit) ▫word = 2 bytes ▫doubleword = 2 words ▫quadword = 2 doublewords

14 Data Representation Even if we know that a block of memory contains data, to obtain its value we need to choose an interpretation Ex: memory content “ ” can either represent: ▫the number 2^{6} + 1 = 65 ▫or the ASCII code of character “A”

15 Data Representation Number Systems ▫Binary/Octal/Decimal/Hexadecimal ▫Converting between various number systems Signed/Unsigned Interpretation ▫Two’s Complement Addition/Subtraction Character Storage

16 Number Systems A written number is meaningful only with respect to a base To tell the assembler which base we use: ▫Hexadecimal 25 is written as 25h ▫Octal 25 is written as 25o or 25q ▫Binary 1010 is written as 1010b ▫Decimal 1010 is written as 1010 or 1010d You are supposed to know how to convert from one base to another.