We've all been there: you need to transfer a batch of documents, maybe a folder full of photos, or some other large data set that's too cumbersome to email yourself, so you turn to the handy USB flash drive. You plug the USB memory stick into your device of choice and watch as files start whizzing along to their new destination—until their transfer comes to a sudden snail's crawl, and you are left watching the progress bar inch forward.

Let's unpack this frustrating phenomenon.

How USB File Transfers Work

The USB standard defines a set of data transfer protocols that allow computers to communicate with devices. The USB flash drive has several practical uses, including transferring files between devices.

When you plug in your flash drive, the computer sends a signal requesting information (such as its capacity and the type of file system being used). The device then responds with this info so the computer knows how best to interact with it.

Hand holding USB flashdrive

After exchanging basic settings, the two systems begin negotiating for an optimal speed at which they can send and receive files over their connection; this allows them both to operate at peak performance without overwhelming each other's capabilities or bogging down due to incompatibilities between hardware components (such as processor speeds).

This kind of auto-negotiation process results in different levels that are referred generally known as "low" or "full" speeds when talking about USB transfers specifically: low speed typically means 1 Mbps, whereas full speed translates into 12 Mbps (or faster depending on newer iterations such as USB 3.0).

Top 5 Reasons USB Transfer Speeds Slow Down

Once these initial negotiations have been completed, most users expect their data transfer rates to stay constant throughout an entire session. Unfortunately, several factors, including but not limited to the type(s), size(s), and the number of files being transferred, can cause a slowdown during actual file-transferring activities.

1. The Type and Size of Files Being Transferred

The most obvious explanation for a slow transfer rate is the size and type of files transferred. Large video or audio file format types, as well as images with high resolution, can take up much more bandwidth than simple text documents, meaning it will take longer to move them from one location to another.

Even if both machines are connected via USB 3.0—which offers speeds up to 10x faster than its predecessor—the transfer speed can be significantly impacted by file size and type.

Video editing software running on a iMac

The largest file types include uncompressed audio and video (such as WAV or MPEG), large databases, programs/applications, and ISO files for CD images. JPEG and GIF images are smaller but still require more data than text documents.

2. The Number of Files Transferred at Once

Another factor that can slow down USB transfers is the number of files being transferred simultaneously: The larger your batch size (the total amount of items you're transferring) and the higher their combined file sizes, the greater strain it will put on both systems to move them from one place to another in an efficient manner—which could result in slower transfer speeds overall.

If you're dealing with multiple large files, try splitting up your batch into smaller chunks and transferring them separately. If that doesn't do the speed trick, you might need to transfer files one at a time, as annoying as that solution might be.

3. Fragmentation

Wise Care 365 defragmentation software

Users can try breaking up the file batch to increase transfer speed, but results get dicey when system-derived factors try to break up files. Let's talk fragmentation.

When you transfer files via a USB device, the data can become fragmented due to various factors, including system stability (or lack thereof), hardware/software incompatibilities between devices, and bad sectors on your memory stick. These variables prevent complete reads of large chunks of data, leading to slower transfers as each piece must be sent separately instead of together in one continuous stream.

To combat fragmentation issues with USB transfers, regularly defragment both disks involved; turn off any background programs running simultaneously that might interfere with performance, and ensure all drivers are up-to-date for maximum compatibility across systems participating in the exchange.

In the event of a data disaster (corrupted or accidentally deleted files), you might still be able to recover. Check out our guide to restoring lost files on a USB flash drive.

4. Caching

Review Details Window Containing Cache Files

Caching is a process used by operating systems to store (or "cache") files for faster access. Unfortunately, this can slow down the transfer rate of data over USB devices because instead of reading from the source file each time it needs something, your computer will read from its stored cache—which may have become outdated compared to what was transferred across.

To fix this issue and maintain optimal speed during transfers via USB memory sticks or external hard drives, make sure you're regularly clearing out old caches on both machines involved to ensure they are always up-to-date with current versions of exchanged documents/data sets.

5. Device and Driver Compatibility Issues

Compatibility issues between USB devices and their drivers can also be a source of transfer rate slowdowns. For example, suppose you're using an older device with newer hardware or vice-versa. In that case, the two systems won't necessarily "talk" to each other properly—which could result in slower speeds when transferring files between them.

Hand plugging flashdrive into laptop

To ensure optimal performance from your memory stick transfers (and any others involving external drives), make sure all relevant drivers are up-to-date. Check both machines participating in the exchange before beginning data movement activities. If you need to troubleshoot further, triage one element at a time to isolate and identify the source of incompatibility.

Go Forth and Transfer

We hope we have shed some light on the causes of slow USB transfers and provided you with helpful tips to speed things up. And if you still suffer from slow transfer speeds despite following our advice, it might be time to get a new device.

Understanding the under-the-hood aspects of USB data transfers is the first step to performance optimization. Now that you know more about how these devices work, go forth confidently—and enjoy those speedy file exchanges!