1 Experiment 0 COE 205 Computer Organization & Assembly Language Programming Term 043

2 Outline Definition of a program Instruction atomicity Assembly language Tools Setting up the environment Policy

3 Definition of a Program A sequence of instructions and data that causes a machine to perform a given task. An Instruction has two fields: Operation & Operands ▪Operation (Opcode) ▪Operands: Data ADDITION A B Y AdditionOperation A & BData Y ← ADD A, BInstruction

4 An instruction is atomic. ▪Indivisible ▪Non-interruptible operation Hardware ensures the non-interruptible execution of an instruction. A complex operation is made of simple instructions. Example: ▪ Multiplication - SHIFT - ADD Instruction Atomicity

5 A User’s View of Computer Systems Depends on the degree of abstraction provided by the underlying software We consider a hierarchy of six levels –Moving to the top of hierarchy shields the user from the lower-level details –The top two levels are system independent

6 A User’s View of Computer Systems (cont.) –The other lower four levels are system dependent Assembly and machine languages are specific to a particular processor One-to-one correspondence between assembly language and machine language

7 A User’s View of Computer Systems (cont.)

8 General Properties of a Personal Computer I/O devices – keyboard, scanner, monitor, printer, projector, light pen, etc. Memory unit – where program is kept (debug, d100 lets look at memory) (u 100 unassemble memory, see what is there ) CPU – registers, ALU and stack pointer, control unit and IP (instruction pointer)

9 RAM-Random Access Memory This is where our program stays when we run it. 1600:0100 is an example of a RAM address.

10 ROM–Read Only Memory ROM is read only memory and cannot be changed. ROM has a program burned in the chip. PROM EPROM is erasable programmable read only memory and is expensive and is done with very special equipment. EEPROM

11 BOOTUP- FIRMWARE Firmware lies between hardware and software. Firmware is the software that is burned into the chip. When you turn on the PC. An address is loaded into the CPU’s IP. The address is of the ROM’s firmware. This firmware program is called the BOOTSTRAP program. Then the program runs and loads the operating system. The computer is ready to be used !

12 ROM BIOS Address 0 – 1024 interrupt vectors – (2028 – 4096) BIOS Data (about ) – 640 KB (about 640,000) RAM for your program Above 640KB < 1 MB Video Memory MB – 1.5 MB ROM BIOS – this is Basic Input Output System.

13 Real Mode / Protected Mode All PCs even the real old ones start in REAL MODE where the first 1 MB is usable. All modern operating systems such as LINUX, Widows 95/98/2000/Millennium / XP immediately switch to PROTECTED MODE letting us use all the memory (except ROM BIOS and where the OS is located and memory where other’s programs run)

14 CPU Contained in one IC – integrated circuit 8080, 80x86 = 80286, 80386, 80486, etc. Pentium, Pentium 2, Celeron (similar), Pentium 3, Pentium 4, etc. ALU – arithmetic logical unit CU – control unit Fetch, decode, execute

15 A Small Program in Debug C:\windows> debug - a :0100 MOV AX,5 1600:0103 INC AX Hit Enter -r -t Watch IP and current instruction

16 Machine Cycles Business Executives, e.g., Discuss Machine Cycles when they say their PC is 900 MHZ or 3 GHz. Each command such as MOV AX, 5 (move 5 to AX register) takes a few computer cycles to execute. The faster your computer, the more cycles per second it performs. Cycles per second.

17 Advantages of High-Level Languages Program development is faster –Higher level instructions = less coding –Some simple high-level language instructions can be expressed by a single assembly instruction –But most high-level language instructions need more than one assembly instruction Programs maintenance is easier –For the same reasons as above Programs are portable –Contain few machine-dependent details – Can be used with little or no modifications on different types of machines –Compiler translates to the target machine language

18 Why Program in Assembly Language? Two main reasons: 1.Efficiency Space-efficiency Time-efficiency 2.Accessibility to system hardware Assembly language can be used as a tool to learn computer organization –You will know more about the organization and internal workings of a computer system

19 Space-efficiency Assembly code tends to be more compact than when written in HLL. Not a big plus point for most applications Code compactness is important in some cases –Portable and hand-held device software

20 Time-efficiency Assembly language programs tend to run faster –Only a well-written assembly language program runs faster Time Convenience – (Graphics, hardware drivers) Time Critical – (Aircraft navigational systems, Process control systems, Robot control software, Missile control software)

21 Accessibility to system hardware System software typically requires direct control of the system hardware devices –Assemblers, linkers, compilers –Network interfaces and other device drivers –Video games

22 Bits and Bytes 1 or 0 is a bit 4 bits = a nibble (1/4 of a register) 8 bits = 1 byte 2 bytes = 1 word = register size 1024 bytes = 1 KB = 1kilobyte 1,048,576 bytes = 1 MB = 1 megabyte 1,073,741,824 bytes = 1 GB = 1 gigabyte

23 BITS, decimal, hexadecimal 0 off, 1 on 1001 = 9 01 = = 10 or A 10 = = 11 or B 011 = = 12 or C 100 = = 13 or D 101 = = 14 or E 110 = = 15 or F 111 = = 8

24 Bits, Bytes, OpCode Viewing machine code equivalent of instruction set C:\WINDOWS>debug -a C:0100 MOV AX,5 106C:0103 -d 100 B8 05 in memory means MOV AX, 05

25 16 Bit Addressing The IBM uses 16 bit addressing which lets us use only 65,536 bytes. How do we address up to 1 MB ? 1600:0100 (Segment Number:Offset) 1600 is really 16000, a zero is added. Then 0100 is the other part added on to give the exact location ! (add 0 to 16-bit segment base value) (offset value) (Physical address)

26 Memory location 106C:0100 This is a memory location. It is actually 106C C0 B8 05 is what is there. The OpCode is B8

27 MNEMONIC MOV, INC, are examples of mnemonics –MOV – move –INC – increment

28 CISC architecture Complex Instruction Set Computing This is used by the INTEL 80X86 chips. It is pronounced SISK. CISC architecture uses very few registers so the instructions take many cycles and run slower.

29 RISC Architecture Reduced Instruction Set Computing This is used by APPLE 680X0 family chips and one instruction takes 1 machine cycle. Very fast, very efficient, but many registers and more difficult to program since there are more registers and mnemonics to use. SPARC stations use RISC

30 PROGRAMS Programs are basically a set of instructions to do some task. Here is a simple assembly program. MOV AH,02 // get display ready MOV DL,41 // Capital A INT 21h // Interrupt 21 INT 20h //interrupt 20, quit

31 NEW Tools ASCII Chart What is an A (41 hex) MOV AH,02h - monitor MOV DL,41 – 41 is an A INT 21h - interrupt 21 to execute I/O (cout << “A”)

32 Exiting a program INT 21h This is like EXIT_SUCCESS