Solid State Drive (SSD) vs Hard Disk Drive (HDD) - Which One Should You Get?


Choosing between a solid state drive (SSD) or a hard drive is easy once you understand their purpose and what to look for in each.

Hard disk drives store information on a spinning disc called a platter, which is accessed by an actuator arm that has read/write heads attached to it. Hard drives are part of what's known as magnetic storage because they store information by magnetizing and demagnitizing bits of information on the disk. When information needs to be read, the read head descends onto the disk and reads the polarity of the bits to determine whether the bit is a 0 or a 1. A typical hard drive can read anywhere from 80-160 MB/s sequentially. That's 80-160 million different polarities in a second! In normal circumstances, however, files will be fragmented all over your hard drive, which means your read heads often need to access multiple locations on the hard drive to fetch a single file. The time it takes for the head to "seek" the location on the hard drive is what kills hard drive performance.

Solid state drives have no spinning disks, and therefore eliminate the problem of seeking information. Solid state drives store information to a pool of floating gate transistors known as NAND flash. NAND flash has the ability to maintain a charge even after being powered off, unlike DRAM, which needs to be pumped with electrons continually to maintain data. Solid state drives are much slower than main memory, but are still much faster than magnetic discs.

SSD vs HDD Comparison
       

AttributeSolid State DriveHard Disk Drive
Capacity1TB Notebook, 4TB Desktop2TB Notebook 10TB desktop
Write Speed200-550MB/s50-120MB/s
Boot Time10-13 seconds30-40 Seconds
Seek Time0.1 - 1ms9-12ms
Failure Rate2 million hours1.5 million hours
NoiseNoneAudible clicks & spinning
Power Use2-3 Watts6-7 Watts
VibrationNoneVibration from spinning platters
Cost per GB$0.20$0.03


Performance

Performance is usually measured by read/write speed and seek time. While hard disk drives can read data quickly sequentially, it slows down dramatically when reading multiple number of small files. This is because every time a file needs to be read the actuator arm has to change position to find the file. This is not a problem for solid state drives because solid state drives do not "seek" files like regular hard drives do.

So which one should I get?

To strike the perfect balance, I recommend getting a 250-500GB solid state drive as your boot drive to greatly speed up your operating system, and a 1-2TB hard drive for file storage. Just because solid state drives are significantly faster does not mean that you actually always need that speed.