What is HDD and how it different from SSD?

What is HDD and how it different from SSD?

A computer hard disk drive (HDD) is the mechanism that controls the positioning, reading, and writing of the hard disk, which furnishes data storage. Hard disks are packaged as a unit and either term can refer to the whole unit. It's a non-volatile computer storage device containing magnetic disks or platters rotating at high speeds. It is a secondary storage device used to store data permanently, random access memory (RAM) being the primary memory device. Non-volatile means data is retained when the computer is turned off. The hard disk was created in 1953 by engineers at IBM who wanted to find a way to provide random access to high capacities of data at a low cost. The disk drives developed were the size of refrigerators, could store 3.75 megabytes of data and began shipping in 1956. Hard disk drives can be found in desktop computers, mobile devices, consumer electronics, and enterprise storage arrays in data centers. Memorex, Seagate, and Western Digital were other early vendors of hard disk drive technology. By the mid-1980s, 3.5-inch and 2.5-inch form factors were introduced, and it was at this time they first became a standard in personal computers.

Typically it spins at 5,400 to 15,000 RPM. The disk moves at an accelerated rate, allowing data to be accessed immediately. Most hard drives operate on high-speed interfaces using serial ATA (SATA) or serially attached technology. When the platters rotate, an arm with a read/write head extends across the platters. All data is stored magnetically, allowing information to be saved when power is shut off. Hard drives need a read-only memory (ROM) controller board to instruct the read/write heads how, when and where to move across the platters.

Hitachi released the first 1 TB hard drives in 2007. In 2015, HGST announced the first 10 TB hard drive.


A modern HDD records data by magnetizing a thin film of ferromagnetic material[e] on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such as run-length limited encoding,[f] which determines how the data is represented by the magnetic transitions.

How does it different from SSD?

  • The traditional spinning hard drive is the basic non-volatile storage on a computer. That is, information on it doesn't "go away" when you turn off the system, unlike data stored in RAM.

  • A hard drive is essentially a metal platter with a magnetic coating that stores your data, whether weather reports from the last century, a high-definition copy of the original Star Wars trilogy, or your digital music collection. A read/write head on an arm accesses the data while the platters are spinning.

  • An SSD does functionally everything a hard drive does, but data is instead stored on interconnected flash-memory chips that retain the data even when there's no power present.

  • Flash chips are of a different type than the kind used in USB thumb drives and are typically faster and more reliable.

  • SSDs are consequently more expensive and much smaller than HDDs.

  • Hard drive technology is relatively ancient in terms of computer history whereas the SSD has a much shorter history. The first primary drives that we know as SSDs started during the rise of netbooks in the late 2000s.

  • An SSD-equipped PC will boot in less than a minute, and often in just seconds. A hard drive requires time to speed up to operating specs, and it will continue to be slower than an SSD during normal use.

  • Because of their rotary recording surfaces, hard drives work best with larger files that are laid down in contiguous blocks. That way, the drive head can start and end its read in one continuous motion.

  • Hard drives are more plentiful in the budget and older systems.

  • Users who prefer to download their media files locally will still need a hard drive with more capacity.

  • HDDs consists of a head and a revolving disk. The data is written by the head on the revolving disk.

  • The Storage Capacity of the HDDs is basically the maximum. The HDDs are available in the TBs, HBs, ZBs. They are also used in the Servers for storing the Huge amount of Data.


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Stock photo from Kitsana1980



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