Summary of basic program development knowledge-Hard Disk partitioning

1. Head
The head is a key component of the hard disk to read data. Its main function is to convert the magnetic information stored on the disk to an electrical signal for external transmission, the working principle is that the resistance value of special materials changes with the magnetic field to read and write data on the disk. The quality of the head determines the storage density of the disk.

2. Track
When a disk is rotated, if the head is kept at a position, each head will draw a circular track on the disk surface, which is called a track. These channels are invisible to the naked eye, because they are only some of the magnetization of the disk surface in special ways, and the information on the disk is stored along such a track. The adjacent channels are not closely related to each other. This is because magnetic fields affect each other when the magnetization are too close, and it also brings difficulties to the reading and writing of the head.

3. Cylinder
A hard disk is usually composed of a group of overlapping disks. Each disk is divided into equal tracks and numbered from 0 on the outer edge. A Cylindrical disk is formed with the same number of tracks, it is called the cylindrical disk. The number of cylinders on a disk is equal to the number of tracks on the disk. Because each disk has its own head, the number of disks equals to the total number of cores. The so-called hard disk CHS (cylinder), head (head), Sector (sector), as long as you know the number of CHS of the hard disk, you can determine the capacity of the hard disk, hard disk capacity = Number of cylinders * Number of magnetic heads * number of sectors * B.

4. Sector sector
Each track on the disk is divided into several arc segments, which are the disk sectors. Each sector can store 512 bytes of information. When the disk drive reads and writes data to the disk, the Unit is slice.

5. Absolute sector
Cylindrical/head/sector to uniquely locate the representation of each region on the disk

6. Relative sectors
It's just a number. This number corresponds to an absolute sector cylindrical/head/sector.
However, the relative sector 0 does not correspond to the cylindrical 0 head 0 sector 1. This is because the operating system is limited to access permissions from an absolute position.

Personal Understanding
The read/write unit of the hard disk is a sector. Each sector stores 512 bytes of information. Theoretically, this is not necessary, but it does not seem to have taken any other value.

The old hard drive has the same number of sectors in each ring. Because the concentric circle is closer to the center, the smaller the diameter of the circle, the arc length of the slice is proportional to the distance between the track and the center. Because each slice stores data of the same byte unit, the arc length of the slice is inversely proportional to the data storage density.
The number of sectors in the old hard drive per lap and the storage data volume in each sector are fixed. the disk capacity can be calculated using the head cylindrical sector.
The number of magnetic heads (heads) indicates that the hard disk has a total of several heads, that is, the number of disks with a maximum size of 255 (stored in 8 binary bits );
Cylinders indicates the number of tracks on each disk of the hard disk. The maximum value is 1023 (which is stored in 10 binary bits );
The number of sectors (sectors) indicates that each track has several sectors. The maximum value is 63 (6 binary bit storage );
The maximum disk capacity is:
255*1023*63*512/1048576 = 7.837 GB (1 m = 1048576 bytes)
Or hard disk vendor commonly used units:
255*1023*63*512/1000000 = 8.414 GB (1 m = 1000000 bytes)

If the storage density of the New Hard Disk sector is the same, the arc length is proportional to the storage density. The diameter of the outer ring track is greater than that of the inner ring.
The number of sectors in the new hard drive per lap is not fixed. You need to use a linear method to calculate the hard disk capacity.

The system calculates the number of all sectors. Starting from 0, the number of each slice is the logic address of the slice.

DOS is from the cylindrical 0 head 1 Sector 1 (the second layer of the hard disk is the outermost ring of the first sector of the track) at the beginning, that is, all the sectors on the first layer of the hard disk are retained for the relative sector 0 corresponding to the cylindrical 0 head 1 Sector 1 cylindrical 0 head 0 (the outermost ring track on the first layer of the hard disk)
Assume that each track has 17 sectors (more actually) cylindrical 0 head 1 Sector 1 number 0 remaining sector number 1 to 16 (Sector number starting from 1 cylindrical and head number starting from 0 Number top layer disk corresponding to the head is 0 the cylinder corresponding to the outermost ring track of the head is 0 cylinder 0 cylinder 0 the first sector of the head is 1 sector ), then there are 17 sectors on the cylindrical 0 head 2 (that is, the outermost ring track on the third-layer disk of the hard disk), ranging from 17 to 33. it is not until all the sectors on the cylindrical head (that is, until the outermost ring track of the disk at the bottom of the hard disk) are numbered, then move it to the cylindrical 1 Head, 0 sectors, 1 (the first sector of the first disk of the hard disk in the second ring of the track, what is written in this document is the first sector in the second ring of the second layer of the first sector of the cylindrical head 1 on the 0 sector is still reserved? What about cylinder 2 Head 0? And so on? I don't think it should be the first round of the first layer. All other logic numbers will be retained, that is, press the fan area number, head number, and cylinder number (that is, from the outer to the inside, from the outermost ring to the bottom, and then from the second ring to the bottom until the end of the last layer of the innermost ring) consecutive distribution of DOS fan area numbers in the increasing order

7. Primary Partition
A primary partition, also known as a primary disk partition, is a type of partition like an extended partition or a logical partition. The primary partition cannot be divided into other types. Therefore, each primary partition is equivalent to a logical disk, but the primary partition is directly divided on the hard disk, and the logical partition must be established in the extended partition ).

8. Expand Disk Partitions
A partition type that can only be created on a basic master startup record (MBR) disk. If you want to create more than four volumes on a basic MBR disk, it is very useful to extend the disk partition. Unlike the primary disk partition, do not use the File System to format the extended disk partition and assign it a drive letter. Instead, you can create one or more logical drives in the extended disk partition. After creating a logical drive, you can format it and assign it a drive letter. An MBR disk can contain up to four primary disk partitions, three primary disk partitions, and one extended disk partition. Multiple logical drives can be created in the extended partition.

9. system partition
System partition is a commonly used term in Windows operating systems. It mainly refers to the partition used to start Windows. Generally, it is in the root directory of the partition, contains the Startup file of the operating system (such as boot. INI, ntldr, etc ).

Personal Understanding
Partitioning refers to dividing a hard disk into areas of the same or different sizes. The operating system divides the hard disk into Several partitions, and then creates a file system in each partition to write data files.
The hard disk only saves 64 bytes of storage space for the partition table, and the parameters of each partition occupy 16 bytes. Therefore, the master boot sector can only store data in four partitions. That is to say, a physical hard disk can only be divided into four logical disks.
In fact, all partitions can be regarded as the primary partition. The primary partition has no special significance. It is mainly for extended partitions.
The primary partition cannot be divided into other types. Therefore, each primary partition is equivalent to a logical disk.
A maximum of four primary partitions can be created. At least one primary partition must be created. If four primary partitions are created, no more extended partitions can be created.
An extended partition is a special type of partition. A primary partition records certain information in a specified slice within the partition, indicating the start and end slice of a logical partition. This information can be considered as a partition table of a logical partition.
Extended partitions can be divided into several logical partitions. All logical partitions are part of extended partitions.
Each partition has a partition table to Record Partition information. The partition table consists of four items, each item has 16 bytes, 64 bytes, and each item describes the basic information of a partition.
Generally, four items in the first primary partition table are used to save information about other primary partitions and extended partitions respectively.
For example, a disk has three primary partitions. One extended partition Partition Table has four items: 1 primary partition 1 Information (itself) 2 primary partition 2 Information 3 primary partition 3 information 4 extended partition
Generally, a disk has a primary partition and a logical partition. Therefore, only the first two items in the Partition Table are used: 1 in the primary partition, 1 in the primary partition, and 2 in the extended partition.
The primary partition table and all logical partition tables can be logically understood as a single linked list. Each partition table structure is a pointer to itself and a pointer to the next partition.
Data location can be found in a partitioned table.
The Main Boot Sector is the disk with 0 cylinder, 1 Head, and 1 sector. It can be regarded as the first logically arranged in all sectors of the hard disk. the BIOS usually searches for the Information boot system from this sector.
The Boot Sector is available in each partition, but only one primary Boot Sector starts from the primary Boot Sector.
The Main Boot Sector contains two parts: The Hard Disk Master Boot Record MBR (Master Boot Record) and the Partition Table DPT (Disk Partition Table)
The hard disk information and boot program hard disk information are recorded in the Master Boot Record to check whether the boot program is correct at startup to boot the system boot program on the master partition.

10. File System
Data Structures of file management software (programs), files, and files
A system that organizes and allocates buckets, stores files, and protects and searches stored files.
Create files, store, read, modify, and dump files, control file access, and revoke files when they are no longer in use.
The file system is the method and data structure used by the operating system to identify files on disks or partitions, that is, to organize files on disks.
A few programs (such as system kernel-defined file system programs) directly operate on the disk or the original sector of the partition
Most programs operate on different operating systems based on the file system. Different file systems are used.
Before using a partition or disk as a file system, you need to initialize it and write the record data structure to the disk. This process is called creating a file system.

Personal Understanding
A file system is a data structure defined by an operating system to store data and data storage information, and a general term for some methods to operate files.
The upper-layer software of the file system allows you to conveniently save, search, modify, and delete data.
Different operating systems may use different file systems
Generally, a file system consists of boot records, file allocation tables, and data areas.