1 The user’s view  A user is a person employing the computer to do useful work  Examples of useful work include spreadsheets word processing developing programs in higher level languages  The internal structure of the computer is totally hidden from the user  Important characteristics for the user are execution speed storage capacity peripheral device functionality

2 Assembly Language  Assembly language commands are a symbolic representation of machine language commands using “English like” keywords called “mnemonics”  Using assembly language commands its much easier to program as compared to machine language in the form of long strings of 1s and 0s  Commands in assembly language have a one-to-one correspondence with machine language commands

3 Example  Some assembly language instructions of the x86 family of computers and their equivalent machine language instructions

4 Useful tools for Assembly Language Programmers The assembler The linker The debugger or monitor The development system

5 The Assembler  Assembler is a program written for converting the assembly language program into its equivalent machine language program, and the process of conversion is called the assembly process  The assembly process can also be done without using a computer, but it is very tedious and error-prone  An “assembler” that runs on one processor and translates an assembly language program into the machine language of another processor is called a “cross assembler”

6 The Linker When developing large programs, separate modules can be developed and assembled by different persons working at the same time The linker links those different modules together to form a single module for loading and execution. It also resolves cross references and determines the starting point for execution of the program

7 The Debugger Working in assembly language is tedious and error-prone “Run-time” errors often crash the system instead of smoothly returning the user to the operating system A “debugger”, also called a “monitor”, is a computer program used to help in finding the logical errors in the program

8 The Debugger (continued…) Useful functions which are available with most of the debuggers include: Display and alter the contents of memory, CPU registers and flags Disassembly of machine code Single-stepping and breakpoints

9 Differences between HLLs and Assembly Language In general, there is a “many- to-many” mapping between HLL and equivalent assembly language constructs

10 Differences between HLLs and Assembly Language (continued…) In HLLs type checking is provided  Verifies proper use of variables at compile time  Allows compiler to determine memory requirements  Helps detect bad programming practices

11 Difference between HLLs and Assembly Language (continued…) Most machines have no type checking  The machine sees only strings of bits  Instructions interpret the strings as a type: usually limited to signed or unsigned integers and FP numbers  A given 32-bit word might be an instruction, an integer, a FP number, or 4 ASCII characters

12 General operation of a stored program computer (continued) In case of branch instructions, the contents of the PC are replaced by the address of the next instruction contained in the present branch instruction, and the current status of the processor is stored in a register called the Processor Status Word (PSW)

13 General operation of a stored program computer (continued) This entire process of reading memory, incrementing the PC, and decoding the instruction is known as the Fetch And Execute principle of the stored program computer.

14 Concept of the ISA ISA stands for Instruction Set Architecture and it could be viewed as a model for the computer It includes the instruction set, memory space and all the programmer-accessible registers It serves as the interface between the program and the functional units of the computer

15 The computer architect’s view concerned with design & performance of the entire system designs the ISA for optimum programming and optimum performance of implementation designs the hardware for best implementation of the instructions

16 The computer architect’s view (continued…) uses performance measurement tools, such as benchmark programs, to see that goals are met or not balances performance of building blocks such as CPU, memory, I/O devices, and interconnections meets performance goals at lowest cost

17 Useful tools for the computer architect Software models, simulators and emulators Performance benchmark programs Specialized measurement programs Data flow and bottleneck analysis Subsystem balance analysis Parts, manufacturing, and testing cost analysis

18 The logic designer’s view Designs the machine at the logic gate level Determines whether the architect meets cost and performance goals A single person or a single team may be performing the job of a computer architect and a logic designer

19 Useful tools for the logic designer CAD tools  Logic design and simulation packages  Printed circuit layout tools  IC (integrated circuit) design and layout tools Logic analyzers and oscilloscopes Hardware development systems

20 Concept of the Implementation Domain The implementation domain is the collection of hardware devices with which the logic designer works

21 Concept of the Implementation Domain (continued…) Examples of the implementation domain  TTL or ECL chips  Gallium arsenide chips  PLAs or sea-of-gates arrays  VLSI on silicon

22 A 2-1 multiplexer in different implementation domains 1. Generic logic gates (abstract domain) (a) Abstract view of Boolean logic O I0 S I1

23 A 2-1 multiplexer in different implementation domains (continued…) 2. National Semiconductor FAST Advanced Schottky TTL (VLSI on Silicon)

24 A 2-1 multiplexer in different implementation domains (continued…) 3. Fiber optic directional coupler switch (optical signals in LiNbO3) S (c) Optical switch implementation O I1 I0

25 Classical Logic Design vs. Computer Logic Design The classical logic design usually deals with the state diagram. It implements sequential logic considering machine as a finite state machine. However, the traditional techniques used in logic design cannot be efficiently used in the design of computers.