Chapter 2 Parts of a Computer System -----how the memory （内存） and CPU look to the assembly language programmer for IBM PC and compatible （兼容） systems which.

Chapter 2 Parts of a Computer System

-----how the memory （内存） and CPU look to the assembly language programmer for IBM PC and compatible （兼容） systems which have Intel 80x86 CPU

Aims

Introduce memory system in IBM PC Introduce registers （寄存器） in 80X8

6 CPU Introduce I/O device Introduce software used in assembly lan

guage programming

Outcomes

Master the concepts , model of the memory in IBM PC

Master the registers in 80x86 CPU Mater the software that used in

programming with assembly language

Know I/O device in IBM PC

PC computer system Hardware

Central processing unit (CPU), memory circuits, keyboard, monitor and other input/output device

Software Refers to the programs that the

hardware executes System software Application software

History of Intel CPU

We will discuss PC based on Intel CPU.So let’s look at the history of Intel CPU.

The Microprocessor Age

4-bit microprocessors Intel 4004, the world’s first one, 1971 Intel 4040, an updated version of 4004

8-bit microprocessors Intel 8008, 8080,8085 Motorola MC6800, Zilog Z80

The Modern Microprocessor

In 1978, Intel released the 8086 microprocessor; a year or so later, it released the 8088. Both devices are 16-bit microprocessors. They can run faster than 8085 and address （寻址） 1M bytes of memory.

The Intel family of microprocessors

8086/8088, 80186/80188 80286 80386 80486 Pentium, MMX Pentium Pentium II, Pentium Pro Pentium III Pentium 4, Pentium TH

The Future of Microprocessors Lots of new technology, used for parallel processin

g ( 并行处理 ) Superscalar ( 超标量 ) Superpipelining ( 超级流水线 ) SIMD (Single instruction multiple data) Hyper-Threading( 超线程 )

64-bit microprocessor EPIC (Explicitly Parallel Instruction Computin

g) in Itanium

Personal Computer System

Memory system ( 存储器系统 )DRAM, SRAM, Cache, ROM, EEPROM, Flash memory

I/O system ( 输入输出系统 )Mouse, Keyboard, Monitor , Disk drive, DVD drive, Printer, Plotter, Scanner

Microprocessor ( 微处理器 ) = CPU (central processing unit 中央处理单元 )

Bus ( 总线 ) Data bus, control bus,address bus

Memory system Microprocessor I/O system

Buses

2.1 PC hardware: Memory

Memory in an IBM PC or compatible microcomputer is logically a collection of “slots”, each of which can store one byte （字节） of instructions or data

Little Endian

How to store a word (two bytes) in the memory?--Intel’s method: little endian ( 小端方式 )

The low byte goes to the low memory location, and the high byte goes to the high memory address.

An alternate method: big endian ( 大端方式 )

Data in memory

34h

12h

78h

56h

341234h

56781234h

low

high

RAM & ROM Read-only memory (ROM)

Permanently retain their contents and can be read from but not written to.

Random access memory (RAM) Can be written to read from by program

instructions The contents of RAM chips are lost when

the computer’s power is turned off

Physical address （物理地址） Each memory byte has a 32-bit/20-bit

numeric label called physical address

Prior to the 80386 chip

Processors has 20-bit address bus, so they can only directly address 220 bytes of memory. Range from 00000h to FFFFFh 1M

Up to 80386

Processors has 32-bit address bus, so they can only directly address 232 bytes of memory. From 00000000h to FFFFFFFFh

A PC can contain up to four gigabytes memory

Memory models （内存模式）

32-bit memory model Flat memory model （平展内存模式） Segmented memory model （分段内

存模式） 16-bit memory model

Real address mode memory model（实地址内存模式）

Real address memory mode （实地址模式）

Real address allows the CPU to address only the first 1M bytes of memory space, which is called either the real memory ( 实存储器 ) or conventional memory ( 常规存储器 ).

Memory is visualized as a collection of segments, each segment 64Kbytes long, starting on an address that is multiple of 16.(paragraph)

A segment is a section (an area) of memory.

Segment ( 段） The CPU may use many segments in the program.

For instance, a typical assembly language program consists of at least three segments: code segment ( 代码段 )

(holds the code, i.e. programs or procedures) data segment ( 数据段 )

(contains the most data used in a program) stack segment ( 堆栈段 )

(the area of memory used for the stack)

Memory reference

Memory reference depends on its segment number and a 16-bit offset from the beginning of the segment. Normally only offset is encoded, and

the segment number is deduced from the context.

Logical address and physical address

In the real mode, the physical address ( 物理地址 ) is the 20-bit address that is actually put on the address bus. This address can have a range of 00000H ~ FFFFFH.

The logical address ( 逻辑地址 ) consists of a segment address and an offset address. We’ll use logical address in programming. Segment address : offset address

Segments and offsets A combination of a segment address and an

offset address access a memory location in the real mode. segment address ( 段地址 ): the beginning

address of any 64K-byte memory segment offset address ( 偏移地址 ): the location wi

thin the 64K-byte segment range, the distance or displacement ( 位移量 ) above the start of the segment

Segment address In real mode, a segment is 64K in length and can

begin only at a 16-byte boundary. 16-byte boundary means that least significant four

bits are 0000b. This 16-byte boundary (such an address ends in 0H) is often called a paragraph ( 节 ).

Segment address : is most significant 16 bits of starting address

Segment number consists of the first four hex digits of its physical address.

Offset address Offset is the distance from the first byte of the segment to the byte

being addressed. A segment is limited to 64K byte (16-bit) in the real mode,

therefore an offset address can range from 0000H to FFFFH. The offset address is added to the start of the segment to address

a memory location (physical address) within the memory segment.Segment address

Starting address

Offset address

Memory location

1000H

AB00H

1234H

10000H

AB000H

12340H

2000H

3405H

0100H

12000H

AE405H

12440H

Conversion from logical address to physical address

Add the starting address of the segment and the offset

logical address segment address : offset

address

physical

address

1000H : 2000HAB00H : 3405H1234H : 0100H

12000HAE405H12440H

The physical address is calculated by shifting segment value one hex digit and adding the offset value.

32-bit segmented memory model (from 386)

segment numbers are 16-bit long and used as an index into a table that contains the actual 32-bit starting addressing of the segment

add 32-bit offset and starting address to compute the “actual” 32-bit address

map the 32-bit address into physical addresses by paging mechanism

Logical address

segment number(16bit) offset(32bit)

selector（选择器）

Global descriptor table (GDT)

global descriptor

( 描述符）

segment

line address

Linear address space（线性地址空间）

segment base address（段基地址）

segment

line address

Linear address space（线性地址空间）

page

physical address

physical address spaceLine address

Dir.

table offset

Entry

page directory

page table

Entry

page

Paging is optional.If paging is not used, the linear address can be directly mapped into physical address.

paging mechanism Layer of memory management performed

by the operating system and the Intel 80x86 CPU

Paging mechanism is transparent to programmer

Useful when logical address generated by the program exceeds the physical memory address

for programmer

assigns different memory segments to code ,data and a system stack.

Flat memory model

Programs will actually encode 32-bit addresses to logically reference locations in a single memory space where data and instructions are stored.

Is really a 32-bit segmented model with all segment registers containing the same value.

2.2 PC Hardware: CPU

The X86 CPUs contain 16 program-visible registers.

Registers is internal storage location that can be accessed much more rapidly than a locations in RAM.

They are used during application programming and are specified by the instructions using their names.They are used to store information temporarily.

Application registers

Multipurpose (or general-purpose) registers （通用寄存器）

Special-purpose registers （专用寄存器） Segment registers （段寄存器）

IA-32 operating modes （操作模式） Protected mode （保护模式） Real address mode （实地址模式） System management mode SMM （系

统管理模式）

Protected mode

Native state of IA-32. Cab directly execute 16-bit software in

protected, multitasking environment. Virtual 8086 mode （虚拟 8086 模

式）

Real address mode

Implementing the programming environment of 8086 CPU with extension. Can switch to protected mode

Original mode following power-up or reset.

System management mode SMM

This mode provides an operating system or executive with a transparent mechanism for implementing platform-specific functions such as power management and system security.

Data registers / general registers

EAX (AX): accumulator 累加器 EBX (BX): base index 基址寄存器 ECX (CX): count 计数器 EDX (DX): data 数据寄存器

8-, 16- and 32-bit registers Eight 8-bit general-purpose registers:

AH, AL, BH, BL, CH, CL, DH, DLH means high byte in the 16-bit registerL means low byte in the 16-bit registerAH and AL form AX, …

Eight 16-bit general-purpose registers:AX, BX, CX, DX, BP, DI, SI, SP

Eight 32-bit general-purpose registers:EAX, EBX, ECX, EDX, EBP, EDI, ESI, ESPE means 32-bit extended

Special purpose registers

EIP (IP) : instruction pointer 指令指针 ESP (SP) : stack pointer 堆栈指针 EDI (DI): destination index 目的地址寄存

器 ESI (SI): source index 源地址寄存器 EBP (BP): base pointer基址指针

EIP (IP)

EIP addresses the next instruction to be fetched in a section of memory defined as a code segment ( 代码段 ).

EIP points to the next instruction, but can be modified with a jump ( 跳转 ) or call ( 调用 ) instruction.

Cannot be directly accessed by programmer This register is IP (16 bits) in the real mode ( 实方

式 ) and EIP (32 bits) in the protected mode ( 保护方式 ).

Pipelining mechanism （流水线机制）

Prefetching （预取） instruction Starting execution of an instruction be

fore it finishes execution of prior instructions

Increase effective processor speed

ESP (SP)

ESP addresses an area of memory called stack. The stack ( 堆栈 ) memory is accessed using a

LIFO (last-in, first-out 后进先出 ) method. ESP points to the top of the stack, but will be

modified with a push or pop instruction. This register is SP (16 bits) in the real mode a

nd ESP (32 bits) in the protected mode.

EBP(BP)

Mark a fixed slot in the stack This register is BP (16 bits) in the real

mode and EBP (32 bits) in the protected mode.

EFLAGS ( 标志寄存器 ) EFLAGS indicate the condition of the microprocessor and c

ontrol its operation. The 16-bit CPU only contain a 16-bit FLAG register, which

has nine flags: CF, PF, AF, ZF, SF and OF are called conditional flags

( 条件、状态标志 ) indicate condition that resulted after an instruction wa

s executed. TF, DF, and IF are called control flags ( 控制标志 )

control the operation of instructions before they are executed.

CF (carry flag 进位标志 ) Carry holds the carry after addition or the

borrow after subtraction. The carry flag also indicates error conditions as

dictated by some programs and procedures.

3A = 00111010+7C = 01111100

B6 = 10110110

CF=0

AA = 10101010+7C = 01111100

126 =100100110

CF=1

This is the carry flag.

PF (parity flag 奇偶标志 ) Parity is a count of ones in a number expressed as even ( 偶数 )

or odd ( 奇数 ). Parity is a logic 0 for odd parity and a logic 1 for even parity. If a number contains odd binary one bits, it has odd parity. If a

number contains zero or even binary one bits, it has even parity.

3A = 00111010+7C = 01111100

B6 = 10110110

PF=0

3A = 10101010+78 = 01111000

B2 = 10110010

PF=1

ZF (zero flag 零标志 ) The zero flag shows that the result of an arithm

etic ( 算术 ) or logic ( 逻辑 ) operation is zero. If the result is zero, ZF=1; If the result is not ze

ro, ZF=0.

3A = 00111010+7C = 01111100

B6 = 10110110

ZF=0

84 = 10000100+7C = 01111100

100 =100000000

ZF=1

Don’t worry. This is the carry flag.

SF (sign flag 符号标志 ) The sign flag holds the arithmetic sign of the result

after an arithmetic or logic instruction executes. If SF=1, the sign bit (leftmost bit of a number) is set

( 置位 ) or negative ( 负 ); If SF=0, the sign bit is cleared ( 清除、清零 ) or positive ( 正 ) .

3A = 00111010+7C = 01111100

B6 = 10110110

SF=1

84 = 10000100+7C = 01111100

100 =100000000

SF=0

Don’t worry. This is the carry flag.

OF (overflow flag 溢出标志 ) Overflow occurs when signed numbers are added

or subtracted. For unsigned operation, the overflow flag is ignored.

An overflow indicates that the result has exceeded the capacity of the machine.

3A = 00111010+7C = 01111100

B6 = 10110110

OF=1

AA = 10101010+7C = 01111100

126 =100100110

OF=0

58+124

182

-86+124

38

8-bit signed integer: -128 ~ +127

Segment registers A segment register (16-bit) defines the starting addre

ss of a segment. CS: code segment DS: data segment SS: stack segment ES: extra segment (an additional data segment 附

加段 ) FS and GS: supplemental segment registers availab

le in the 80386 and above

Numbers in segment registers

Real address memory mode Number in segment registers are segment

address. Segmented memory mode

Number in segment registers are selectors Flat memory mode

Irreverent to programmer All segment register have the same number.

2.3 PC Hardware: Input/Output Devices

separate port address port address are distinct from ordinary

memory addresses, use instruction to output data or read data from these ports.

Memory-mapped input/output Use addresses in the regular memory

address space for I/O device access.

80x86 architecture

separate port address 64K port addresses a typical I/O device uses three or eight

ports

2.4 PC Software Software: refers to the programs or pr

ocedures executed by the hardware. System software （系统软件）

Operating system（操作系统） Application software （应用软件）

Text Editors （文本编辑器） Language Translators and Linker

Operating system

Software to run other programs. DOS

Command line interface, prompt Windows

Graphical user interface Linux

Open codes

Text Editors （文本编辑器） Software to create or modify text files that

are stored on the disk Text file is a collection of ASCII codes. Source code files are text file Notepad, Word processor， Edit

The extension name of assembly source file is .ASM

Example: test.asm

Language Translators

Language translators are programs that translate a programmer’s source code into a form that can be executed by the computer. Interpreters（解释器） Compliers（编译器）

Interpreters

Interpreters:directly decipher （解释） a source program Interpreter looks at a line of source c

ode and follows the instructions of that line

Slowly

Compliers（编译器） Compliers: starts with source code and p

roduce object code that consists mostly of instructions to be executed by the intended CPU.

Assembler （汇编程序） : like a complier, translates assembly language into machine code. ML.exe

How to use ML.EXE

LINKER（连接软件） LINKER: link object code to make a p

rogram that can be executed. Link.exe

16-bit32-bit

How to use link

Debugger（调试器，调试软件） Debugger: allows a programmer to co

ntrol execution of a program, pausing after each instruction or at a preset breakpoint. Debug.exe Windbg.exe SoftIce.exe

Integrated Development Environments IDE （集成开发环境）

Use a single interface to access an editor, a complier, and a linker. MASM32

MASM32

BUILD—buildc.bat 1

@echo off

if exist "%1.obj" del "%1.obj"if exist "%1.exe" del "%1.exe"

REM 汇编\masm32\bin\ml /c /coff "%1.asm"if errorlevel 1 goto errasm

BUILD—buildc.bat 2

REM 连接\masm32\bin\Link /SUBSYSTEM:CONSOLE /OPT:NOREF "%1.obj"if errorlevel 1 goto errlink

dir "%1.*"goto TheEnd

BUILD—buildc.bat 3

:errlinkecho Link errorgoto TheEnd

:errasmecho Assembly Errorgoto TheEnd

:TheEnd

pause

After build…

Run program

Exercises

P30. Exercises 2.1-- 2 ， 3 P34. Exercises 2.2--1, 2, 3 P34 Exercises 2.3--1, 2