What is Addressing Software?

Addressing is the basis of data recovery technology and the key to locating data and sectors. The concept of addressing is more abstract. In short, it is a process in which the magnetic head locates data on the disc. If you want to find a file on your computer, you may first open My Computer, partition, folder in Windows, and then open the file you are looking for. This is the process of looking for files on the surface, and the process of head searching on the disc is addressing. Why is addressing so important in data recovery? Because when the data is lost, you can't find this file under my computer, partition, folder, or even folder and partition.

The computer has multiple addressing modes, such as immediate addressing mode, register addressing, memory addressing mode, addressing modes related to I / 0 port, and includes direct port addressing and indirect port addressing. ^[1]

Chinese name: Addressing
Foreign name: Addressing

Types of: Computer term
Field: Computer operating system
Classification: Logical and physical addressing

Addressing logical addressing

Logical addressing is to consider all sectors of the hard disk as a cylinder, and the sectors are arranged from 0 to infinity. Of course, the capacity of the hard disk determines the total number of sectors. In logical addressing, the description of a certain sector is a certain (number) sector.

Physical addressing

Physical addressing is also called CHS (Cylinder, Head, Sector) addressing. The three parameters of Cylinder, Head, and Sector have their values marked on the labels on the surface of many hard disks. This is the basis for calculating the size of the hard disk. In physical addressing, the description of a sector is a certain sector of a certain cylinder head.

Hard disk capacity = number of disks x number of cylinders x number of sectors x 512 bytes.

Introduction to Addressing

Immediate addressing

The operands are stored directly in the instruction. The addressing mode immediately following the opcode is the immediate addressing mode. For example: MOV AX, 2345H MOV AL, 0EH. ^[1]

Addressing Register Addressing

When the operand is stored in the memory register of the CPU, the register name can be indicated in the instruction, which is the register addressing mode. For example: MOV AX, BX; ADD AX, BX. ^[1]

Addressing memory addressing

The 8086 instruction system provides the following five memory addressing modes. Direct addressing, register indirect addressing, register relative addressing, base plus indexing and relative base plus indexing. Used to describe the address of the memory location where the operand is located. Since the bus interface unit BIU can automatically reference the segment register to obtain the segment value as needed, these five methods are also the methods of determining the effective address EA of the storage unit storing the operands. The effective address EA is a 16-bit unsigned number. When using these five methods to calculate the effective address, the result obtained is considered to be an unsigned number. ^[1]

(1). Direct addressing: The address code given in the instruction is the effective address of the operand, which is the direct addressing mode.

(2). Register indirect addressing mode

(3). Register relative addressing mode

(4). Base Index Indexing

(5). Relative base indexing addressing method ^[1]

Differences and Applications of Addressing

Both logical addressing and physical addressing are currently used, and many softwares can also be located using both addressing methods. However, due to the relatively complex physical addressing method, three-digit positioning is used, different hard disk sizes have different upper limits, different starting points (Cylinder and Head start from 0, and Sector start from 1). In more use of logical addressing to complete the positioning.

Addressing addressing operation method

It is the address where the specified instruction is to operate. The address method for a given instruction operation is the address method. A complete instruction should include the instruction symbol + operand (of course, those single instructions, such as NOT, etc.) are not included. The operand is the target of the instruction to be executed, that is, the address of the instruction to perform the operation.

We know that there are various storage areas in the PLC, such as physical input and output area P, image input area I, image output area Q, bit storage area M, timer T, counter C, data area DB and L, etc. At the same time, we also know that each area can be measured in bits (BIT), bytes (BYTE), words (WORD), double words (DWORD), or to specify the exact size. Of course, there is no such measurement system for timer T and counter C, they are only measured by bits. From this we can get that to describe an address, it should contain at least two elements: 1. the storage area

2. The specific position in this area, such as: AQ2.0

Where A is the instruction symbol, Q2.0 is the operand of A, which is the address. This address consists of two parts: Q: refers to the image output area; 2.0: it is the 0th bit of the second byte of this image output area. From this, we conclude that an exact address composition should be: [Storage Area Code] [Storage Area Size Code] [Dimension Value]. [Bit Value].

classification:

Direct addressing, in simple terms, is to give the exact operand of the instruction directly. Direct addressing is often used to process data in memory cells. The operand is the value of a memory variable. Addressing. Note: The writing format of the immediate addressing mode and the direct addressing mode is different. The direct addressing address should be written in brackets "[", "]". In programs, direct addresses are usually represented by memory variable names, such as: MOV BX, VARW, where VARW is a memory word variable.

Indirect addressing is the exact operand of an instruction given indirectly. There are two major types of indirect addressing: memory indirect addressing and register indirect addressing.

The memory indirect addressing pointer is used as the exact value unit of the specified memory area. In other words, the pointer does not contain the area identifier, it just indicates a value.

The address given format of memory indirect addressing is: address identifier + pointer. The value contained in the storage unit indicated by the pointer is the exact value unit of the address.

Memory indirect addressing has two pointer formats: single-word and double-word.

The single-word pointer is a 16-bit structure, from 0-15bit, indicating a value from 0-65535, which is the number of the memory area being addressed.

A double word pointer is a 32-bit structure, from 0-2bit, a total of three bits, according to the octal indication of the number of the bit being addressed, that is, 0-7; and from 3-18bit, a total of 16 bits, indicating a from 0 A value of -65535, which is the number of the byte being addressed.

Pointers can be stored in M, DI, DB, and L areas, that is, the contents of these areas can be used as pointers.

Single-word pointers and double-word pointers are very different in use. The single-word pointer memory indirect addressing can only be used in the case where the address identifier is non-bit; due to the bit format of the double-word pointer, there is no restriction on the address identifier. It is also because the double word pointer is a pointer with a bit, so when addressing a byte, word, or double word memory area address, you must ensure that the content of the double word pointer is 8 or a multiple of 8. ^[2]