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Basics of HDD
HDD is a magnetic storage device; data recording is achieved by directional magnetization of a ferromagnetic material. It is done in a polarized manner so that each polar state represents either a 0 or a 1 digital logic level, and consequently, data is read back by detecting the polarity of magnetization.
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A typical HDD comprises of a spindle that holds multiple flat circular disks, onto which the data gets recorded; these are known as platters.
These platters spin at very high speeds and as they rotate past the ‘read-and-write heads’, information is written onto them.
Today, HDDs come with storage capacities as high as 2TB. As there are a lot of components that need to perform specific functions, an integrated circuit [IC] has to be fabricated to enable the HDD to function seamlessly. So, now let us move on to the HDD integrated circuits, and analyze their basic working principle.
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Working of a HDD Integrated Circuit
The disk control circuitry receives and stores requests, exchanges digital data with the client and stores the digital data in RAM. The write channel generates a write signal to write data onto the HDD, and the read channel generates a read signal to read data from the HDD.
The servo circuit generates a motor control output signal to control the spindle motor and the head actuator. Finally, the digital signal processor initiates ‘Read’ and ‘Write’ operations, as needed to perform the requests of the client device.
The digital signal processor also performs file management, generates the motor control input signal, and processes the intermediate read signal to generate a read channel parameter.
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HDD Integrated Circuit Parameters
An HDD IC is responsible for controlling the operation of the HDD at all times. There are many parameters that need to be controlled by the HDD IC; here are some of the important aspects of HDD ICs -
• Data Transfer Rate: This is the rate at which data is transferred from and to the HDD. Data transfer from the HDD occurs in two stages. The data is first put into a ‘data buffer’ from the disk; and later is sent to the processor or peripherals. A typical 7200rpm 3.0 Gbit/s SATA interface can send about 300 MBps from the buffer to the computer.
• Seek Time: The time taken to physically find data on a HDD is called seek time. Seek time ranges from about 2 ms for high-end server drives, to 15 ms for miniature drives, with the most common desktop type typically being around 9 ms.
• Power Consumption: is the power consumed by the HDD per unit time. Nowadays, the seek speed is controlled so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around. This results in improved efficiency and lesser power consumption.
Perfect meshing is required between the spindle, platters and the read-write heads; as all these have to work in tandem for data read or write operations on the HDD.
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The Future of HDD Integrated Circuits
The future scope of controller IC for HDD is to be lighter, thinner, shorter and smaller. The optimal packaging manufacturing process for driver IC for micro HDD is Chip Scale Package (CSP). However, the production and assemble process for CSP is yet to become commercially viable. Ongoing research in this field provides promising future of HDD integrated circuits.
Here's an interesting article on difference between SATA and PCI.
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Wikipedia: Hard disk drive