The Differences Between a USB Flash Drive & an SSD

by Jeff Grundy Google

    Many supplemental media options exist that enable you to add to the storage capacity of your computer including a variety of flash memory cards and drives. Two such flash-memory-based drive devices are solid-state drives and USB flash drives, which use programmable memory chips to store data rather than the magnetic platters used in standard hard drives. Both SSDs and USB flash drives both use flash-memory technology. However, if you are thinking of adding a flash-memory drive to your computer, there are some important differences should be aware of as well.

    Physical Size and Usage

    USB flash drives are usually about the size of a small lighter or your thumb; thus, you may hear people refer to them as thumb drives. In contrast, SSDs use the same form factors as standard desktop and laptop hard drives. SSDs come in four different widths: 1.8-inch, 2.5-inch, 3.5-inch and 5.25-inch. While you must always use a USB flash drive as an external storage device, SSDs can serve as internal or external drives. Manufacturers design SSDs primarily for use inside a desktop or laptop computer. Nevertheless, you can purchase external SSD drives. External SSDs are simply SSD drives inside enclosures that you can connect to a computer via a USB port. Alternatively, you can create an external SSD drive yourself, by purchasing an external hard-drive case with a SATA-to-USB conversion board and cable, installing the drive inside the enclosure and then connecting it to your computer. By using a 2.5-inch or 3.5-inch SSD inside an external enclosure, you also make the storage device portable just like a USB flash drive.


    If you need only to copy the occasional file to a portable device so that you can share it with a friend, the speed of your flash storage drive probably isn't much of a concern. However, if you need to use a flash-memory drive constantly to copy, save or transfer files, speed may be an issue. Most USB flash drives transfer data using the USB 2.0 standard, which means that under optical conditions the devices can read data at 34MB/s (megabytes per second) and write it at 28MB/s. Some newer USB 3.0 flash drives can read and write data much faster, and the fastest ones read and write data at up to 124MB/s. SSDs are significantly faster than even the fastest USB flash drives, and usually transfer data quicker than even traditional platter-based hard drives. Like modern platter drives, SSDs connect to a computer motherboard via a SATA -- or Serial ATA -- cable. However, SSDs can transfer data at up to 360MB/s, whereas traditional drives usually cap out at rates between 120MB/s to 165MB/s. If you want to copy the contents of a 700MB file to a flash-memory drive, it would take you approximately 20 to 30 seconds with most USB drives and only less than 5 seconds in most cases with an SSD.

    Capacity and Cost

    When it comes to storage capacity, both SSDs and USB flash drives are considerably smaller than most platter-based hard drives. The largest commonly available USB flash drives are 256GB in size as of November 2012. Victrorinox does make a 1TB USB flash drive, but at $3000, it is out of the price range of most consumers. The largest SSDs provide 1TB of storage, but most mainstream solid-state drives hold only 128GB to 512GB of data. By comparison, traditional SATA platter hard drives are available in sizes all the way up to 4TB. Because USB flash drives use a cheaper type of flash memory, they are less inexpensive when compared to SSDs. The typical cost of a 128MB USB flash drive is about $80, while an SSD with the same storage capacity will set you back between $90 and $120 depending on the brand you buy. As you look into SSDs with larger capacities, their prices increase significantly. For example, a 512GB SSD usually sells for between $325 and $700. By comparison, major-brand 1GB platter drives often sell for well below $100. Note that all capacity and price data is current as of November 2012 and could change considerably without notice.

    Reliability and Efficiency

    While SSDs cost a lot more than USB flash drives, they are also more reliable. Both types of drives use NAND flash memory to store data, but not the same kind. USB flash drives use multi-level cell memory, which is much cheaper to produce than the single-level cell memory used in SSDs. The MLC memory used in USB flash drives can store 2 bits of data for every cell, resulting in larger possible storage capacities. In fact, some hybrid SSD drives use MLC memory to increase their storage capacities up to 1GB. While SLC memory does not allow for such large storage capacities, it endures much better than MLC memory. Generally speaking, you can only read or write data to a MLC memory cell about 5,000 times. SLC increases the number of possible read/write cycles to about 50,000. The controller boards found in SSDs support wear leveling, which helps to spread read/write operations across more of the cells in the memory chips to make the drives last longer. Controllers in SSD drives also enable advanced hard drive features, such as native-command queuing that optimizes read/write requests and SMART, which enables the computer BIOS to monitor the drive in real time for potential anomalies of problems. There are many other technical reasons why SSDs perform better and are more durable than USB flash drives. However, the bottom line is that SSDs are faster and more reliable than USB flash drives.

    About the Author

    Jeff Grundy has been writing computer-related articles and tutorials since 1995. Since that time, Grundy has written many guides to using various applications that are published on numerous how-to and tutorial sites. Born and raised in South Georgia, Grundy holds a Master of Science degree in mathematics from the Georgia Institute of Technology.

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