excerpt from compilation book

P17

The structure of a typical computer,A central processing unit consisting of a microprocessor chip(CPU) 存储器 The input-output subsystem has three main components.Connect them together with the system bus

存储器是计算机的记忆部件

The central processing unit includes two parts: the arithmetic unit and the controller

I/OSubsystems generally includeI/OThere are two types of external devices, including mass storage devices.

除必要的系统程序外,一般程序（包括数据）is stored in external storage,只有当运行时,才把它从外存传送到内存的某个区域,It is then processed and controlled by the central processing unit

P18

Computer software is divided into two parts: system software and user software,System software is a set of programs provided to users by computer-generated manufacturers,User software is a variety of programs compiled by users themselves

The core of the system software is the operating system,is a collection of system programs.

The main part of the operating system is the resident supervisor

P-19

高级语言的翻译程序有两种方式：One is to first translate the high-level language into machine language,然后再在机器上执行,这种翻译程序称为编译程序

The other is to run the high-level language directly on the machine,一边解释一边执行,这种翻译程序称为解释程序,BASIC就采用这种方式

The translators in the system include the assembler 解释程序 编译程序

P-19中央处理机

CPUThe task is to execute a sequence of instructions stored in memory,除了要完成算术逻辑操作外,,also bearCPUand memory as wellI/O之间的data transfer务

Registers can be divided into visible registers and invisible registers in the program,Visible registers are those used in assembly language programming,Can be specified by directive,Invisible registers refer to registers that are not used in general application design but are used by the system

AX BX CX DX Can be called a data register,用来暂时存放计算过程中所用到的操作数,results or other information

AX作为累加器用,It is the main register for arithmetic operations

BX可以作为通用寄存器使用,Often used as the base address register

CX 可以作为通用寄存器使用,Often used to save count values

DX 可以作为通用寄存器使用,Used for double word operationDX和AX组合在一起存放一个双字长数,DX用来存放高位字,或I/O端口地址

P-20

1.通用寄存器

SP BP SI DIOperands can be stored during operations like data registers,But more often an offset address is provided,Hence the name pointer or index register

2.专用寄存器

SP堆栈寄存器,Used to indicate the offset address of the top of the segment

BP 基址指针寄存器,Available with stack segment registersSSThe association is used to determine the address of a memory location in the stack segment

P-22

FLAGS为标志寄存器,A storage condition code flag,控制标志和系统标志的寄存器

下面介绍标志寄存器

1. 条件码

溢出标志 OF

符号标志 SF

零标志 ZF

进位标志CF

辅助进位标志 AF

奇偶标志 PF

1. The control flag bit is the direction flag（DF)
2. 系统标志位

陷阱标志 TF Single-step operation during debugging

中断标志 IF 当IF为1时,允许CPU响应可屏蔽中断请求

I/O特权级 在保护模式下,用于控制对I/O地址空间的访问

P-24

段寄存器,It is also a special register,Dedicated to memory addressing,Can be used to store segment addresses directly or indirectly,长度为16位

总结：80x86寄存器组：通用寄存器 专用寄存器 段寄存器

P24

16位2进制数可表示2地16The address of the power byte unit,为0-65535,即64K

P25

It takes two bytes to store a word in memory,低位字节存入低地址,高位字节存入高地址

P26

如果用XIndicates the address of a storage unit,则XThe contents of a cell can be represented as （X）,假如X单元中存放着Y,而YYet another address,可用(Y)=（（X））

P-27

把段地址左移4位再加上偏移地址就形成物理地址,

16*段地址+偏移地址=物理地址,每个存储单元只有唯一的物理地址,But it can be composed of different segment addresses and different offset addresses

P32

The communication between the external device and the host is carried out through the peripheral interface,Each interface includes a set of registers,Generally there are three different uses：数据寄存器,状态寄存器,命令寄存器

BIOSStored in read-only memory onlyROM中,his levelDOS更低,更接近硬件