What’s the Difference Between USB and UDISK?

With all the gadgets we post about here at sometimes a word or definition can get twisted on it’s meaning. One of those terms is UDISK. First, please don’t complicate the term into something more than it is. The geogrpahical location on where you live could have a huge part in the term you are using, hearing or reading about!

The Asia / Pacific Rim region use the term UDISK to describe a flash drive. In the United States and Europe the term is USB flash drive, thumb drive or USB key. However, this doesn’t clearly define what the term UDISK means, but rather the colloquialism (word or phrase) used to describe the object.

USB Drive

Simply put, a UDISK is the technical term for a disk hard drive which connects to the host via a USB cable. With magnetic hard drive platters spinning inside an enclosure, UDISKs have a bridge chip regulating the way the drive mounts to an operating system. This chip changes the hard from from IDE protocols, to USB protocols. Standard USB flash drives do not use rotating disks to store data, but use NAND flash memory instead, which enjoys faster speeds as well as increased reliability against shock, pressure, and temperature. Why then, do these UDISK drives exist? Because those spinning disks are cheaper to manufacture as a hard drive than creating a Solid State Drive (SSD) made from NAND memory.

As a point to remember: if your USB flash drive mounts as a UDISK on your computer, than most likely your USB drive has firmware which doesn’t match the memory type and controller combination. The smallest size of a UDISK should be similar to a small hard drive, like 80GBs and going up in capacity from there. Even today, in 2021 an 80GB USB thumb drive is not that common… so if you see a small thumb drive showing up as a UDISK then be careful with it’s use (reliability issue).

If you are still unsure a speed test will certainly help out. Take about 1GB of data and copy those files to the device. If the write speed ranges between 5-50MB/second then it’s a thumb drive. If the write speeds are much faster, say 75MB/second and above, then you have a hard drive. The speed test is an easy thing to do for a non-technical person, simply expand the copy dialogue Windows displays during the process. In that pop-up window will be the speed for the copy process. Below is a screen shot for copying 1GB of data to a USB 3.0 flash drive. Right about the upper limit of a common device at 46MB/s… this IS a flash drive.

Windows copy speed

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Cyrus is currently getting his bachelors degree in computer programing. As a part time job, Cryus writes contributing articles and content for He is an avid swimmer, loves Minecraft and prefers to program in Python.

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