What is an SSD? How solid state drives work

That whirring you hear when you boot your computer or when it wakes from sleep mode is the sound of your hard drive’s magnetic disks beginning to spin. Conceptually not dissimilar to a record player, a hard disk drive (HDD) is an electromechanical device with an actuator arm that positions itself over spinning disks, called platters, in order to read or write information.

While record players top out at 78 rpm, today’s enterprise-grade HDDs can spin at 15,000 rpm. Even at that speed, however, there are unavoidable delays associated with heads finding the spot on the drive that contains the data being requested. And sometimes a drive may need to read from multiple locations in order to complete a command, multiplying wait times.

Why solid state drivies (SSDs) are better

Solid state drives (SSDs), as the name suggests, don’t have moving parts or spinning disks. They use interconnected pools of flash memory that are managed by an SSD controller to deliver speeds far beyond what an HDD can offer.

Some rough examples: SSDs can reduce boot time from around 35 seconds to about 10 seconds. Write speeds for an HDD might be in the range of 50-120Mbit/sec. compared to between 200-500Mbit/sec. for an SSD. An HDD might be able to complete between 50-200 input/output operations per second, while a comparable SDD might be able to do as many as 90,000. And some enterprise grade, rack scale SSDs claim to be able to process millions of operations per second.

SSD prices and reliability 

But despite their performance advantages, SSDs only have a 10% market share compared to HDDs for a couple of reasons. First and foremost, they’re expensive. HDDs today average around 3-4 cents per GB, compared to 25-30 cents for SSDs. For example, a 1TB internal HDD costs around $40, while a comparable SSD costs around $250.

[ Related: SSDs poised to get a lot cheaper ]

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