Reading Notes 5

The author's words:

There are few hardware contacts, and many terms are literal translations. Please forgive me. I try to include the original English words to avoid ambiguity.

 

2.2 disk drive components

The disk drive uses a fast-moving arm to read and write data on disks with the same size as a large record. data is transmitted from the disk to the computer through the R/W header. multiple disks, read/write headers, and controllers are combined. This is usually called hard disk drive-HDD ). data can be read and written to the disk for multiple times. this section describes the details of different disk components, the mechanism for organizing and storing data on disks, and the factors that affect disk performance.

 

Key components of the disk drive include: disk, spindle (spindle), reader, actuator assembly, and controller.

 

2.2.1 platter

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A typical HDD consists of one or more flat circles called platter disks (see Figure 2-3 ). data is recorded on these disks in binary format. A stack of Rotating Disks is enclosed in a box called head disk assembly (hda ). A platter (disc) is a rigid disc with magnetic material covering the upper and lower surfaces. data is encoded by dividing the disk surface's magnetic area (area or domain. both sides of the disk are readable and writable. the number of disks and the capacity of each disk determine the capacity of the entire disk drive.

 

2.2.2 Spindle

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The spindle is connected to all the disks, as shown in Figure 2-3, and the motor connected to the shaft of a motor rotates at a fixed speed. the disk rotation speed is several thousand RPM per minute ). the disk drive axis speed is 7200 RPM, 1,000 rpm, or 15,000 rpm. the disk used by the current storage system is 3.5 inch (90mm) in diameter ). when the disk speed is 15,000 rpm, the outer edge moves at a speed of 1/4 of the sonic speed. as the technology continues to grow, the speed of the disk is not enough.

 

2.2.3 read/write head

Read/write headers (see Figure 2-4) can read data from disks. each disk has two write headers, one on the top and one on the top. when writing data, the reader header modifies the magnetic polarity of the disk surface. when reading data, the head detects the magnetic polarity on the disk surface to read data. during reading and writing, the R/W head will sense the magnetic pole, but will not touch the disk surface. when the rotating shaft is turned, there is a small gap between the disc and the reading and writing head, known as the head flying height ). this small gap will be removed when the rotating shaft is stopped, and the reading and writing head will stop in a special area near the rotating shaft of the disc. this special area is called the landing zone ). the dock is covered by lubricants to reduce friction between the disc and the reading and writing head. the disk logic ensures that the write and read headers stop close to the disk and will definitely land in the dock. if a problem occurs in the disk drive and the write header accidentally hits the part of the disk outside the dock, the Head crash occurs. when a head hit occurs, the magnetic material covered on the disk is destroyed, which may damage the read/write head. headers usually cause data loss.

 

2.2.4 actuator Arm Assembly

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The read and write headers are loaded on the actuator arm assembly (driver Arm Assembly), which positions the Read and Write headers to the locations where data needs to be read and written on the disk. the Reading and Writing headers of all disks are attached to a drive arm and moved simultaneously on the disk. note that no disk has two write headers, each of which is shown in Figure 2-4.

2.2.5 Controller

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The controller is a printed circuit board attached to the bottom of the disk drive. it consists of a small processor, memory, circuit and firmware. the firmware controls the power supply and speed of the motor to the shaft motor. it also controls read/write operations by controlling the drive arm and switching different read/write headers, and optimizes data access.

2.2.6 physical disk structure

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The data on the disk is recorded on the track, and the track is the concentric circle around the axis on the disk, as shown in Figure 2-5. the track is numbered, starting from the outer edge of the disk, which is 0, 1, 2... the number of tracks with no feet on the disk determines how closely the tracks on the disk are arranged.
Each track is divided into smaller units called the sector (sector. the slice is the minimum addressable unit in the storage unit. the structure of the channels and sectors is completed by the manufacturer's formatting operation. the number of sectors on each track varies depending on different disks. the disk of the first PC has 17 sectors per lap. the current disk can have a much larger number of sectors per lap. each disk has thousands of tracks, depending on the disk density in the physical dimension.

Typically, one slice stores 512 bytes of user data, although some disks can be formatted as larger slice sizes. in addition to user data, the slice also stores other information, such as the slice number, header number, disk number, and track number. this information helps the Controller locate data in the disk, but it is also a consumption of disk space. the result is that the size of the formatted disk is smaller than that of the unformatted disk. drive manufacturers generally advertise the capacity when no format is available. For example, a GB hard drive can only contain user data of GB, and the remaining 34.3g is used to hold metadata.

Cylinder is a collection of identical tracks on both sides of each drive disk. The position of the drive header is the number of the cylinder, not the number of the track.

 

2.2.7 zoned bit recording

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Because the disc is composed of magnetic channels with the same center, the magnetic track of the outer ring can save more information than the Magnetic Track of the inner ring. The magnetic track of the outer ring is physically longer than that of the inner ring, as shown in Figure 2-6 (). on an old disk drive, the magnetic track of the outer ring has the same number as that of the inner ring, so the data density is very low in the outer ring. this is inefficient at using available space. zone bit recording can efficiently use disks. see figure 2-6 (B). This mechanism groups the track based on the distance from the disk center into zones. these zones are numbered, And the outermost zone is Zone 0. the appropriate number of sectors in each circle is allocated to each zone. Therefore, there are a few destination sectors near the center of the circle, and there will be more sectors in the outer ring. however, the number of sectors in a zone is the same.

 

2.2.8 Logical Block Addressing
An earlier drive uses a physical address consisting of cylinder, Head, and sector (CHS) to address somewhere on the disk, as shown in Figure 2-7 (), the hosted operating system has to understand the geometric nature of each disk. logical Block Addressing (LBA) (2-7-b) simplifies data access by using linear addresses to access physical data blocks. the disk controller translates the LBA into the CHS address. The host only needs to know the number of disk drive blocks to learn the size. the Logical Block corresponds to the physical sector at a ratio.

 

Figure 2-7 B shows eight sectors, eight heads, and four tubes in each circle. this means 8x8x4 = 256 blocks, so the block number ranges from 0 to 255. each block has its own address. if the slice contains 512 bytes, a disk with a size of 976,000,000 GB after formatting will have more than blocks.

 

Translated from <Information Storage Management>