What is a USB flash drive?
A USB flash drive, also called a thumb drive, USB stick, jump drive, or pen drive, combines NAND flash memory chips with a small controller in one case. The controller handles the USB interface, wear leveling, and bad-block management. There are no moving parts, so the drive is silent and handles drops far better than a hard drive. It draws power from the USB port.
Flash cells wear out after a limited number of write cycles, and inexpensive drives can fail without warning. Treat a flash drive as a way to move data, not as the only copy of anything important.
Speeds and connectors
- USB 2.0 tops out at 480 Mbps. USB 3.x runs at 5 Gbps (USB 3.0, later called USB 3.2 Gen 1) or 10 Gbps (USB 3.2 Gen 2).
- Real transfer speed depends on the flash chips and controller and is often well below the interface maximum, especially for writes.
- USB 3.x Type-A ports and plugs often have blue inserts. A USB 3.x drive works in a USB 2.0 port at USB 2.0 speed.
- USB-C drives and dual-connector drives with both USB-C and Type-A are common for phones, tablets, and newer laptops.
File systems
| File system | Largest single file | Compatibility |
|---|---|---|
| FAT32 | 4 GB minus 1 byte | Almost every device: Windows, macOS, Linux, TVs, cameras, car stereos, and UEFI firmware |
| exFAT | No practical limit for flash drives | Windows, macOS, and current Linux; designed for flash media |
| NTFS | No practical limit for flash drives | Full support in Windows; macOS reads NTFS but does not write it by default |
If copying a large video or an ISO file fails with an error saying the file is too large for the destination file system, the drive is FAT32. Back up its contents and reformat it as exFAT or NTFS.
Bootable USB drives
USB flash drives are the standard media for installing operating systems and running repair and diagnostic tools. Microsoft's Media Creation Tool builds a Windows installer on a drive of at least 8 GB. Copying an .iso file onto a drive does not make it bootable; the image has to be written to the drive with a tool built for that purpose. To start from the drive, select it in the one-time boot menu or put it first in the boot order. USB boot must be allowed in firmware, and Secure Boot may block tools that are not signed. UEFI firmware reliably reads FAT32, which is why many UEFI boot drives use it despite the file size limit.
Security and data loss
- Loss and theft. Small drives are easy to lose. BitLocker To Go encrypts removable drives and can be turned on from Windows Pro, Enterprise, and Education editions. Some drives include hardware encryption with a keypad.
- Malware. Modern Windows does not AutoRun programs from USB flash drives, but a user opening a file can still launch malware. A drive found in a parking lot is a classic social-engineering lure.
- Policy controls. Organizations restrict USB storage with Group Policy, endpoint management, or data loss prevention (DLP) software. The USB permissions setting in BIOS/UEFI can disable USB ports at the firmware level.
- Safe removal. Windows uses a quick removal policy for USB drives by default, but ejecting the drive before unplugging is still safest while files are being written.
- Disposal. Degaussing does not erase flash memory. Use a wipe method meant for flash, or physically destroy the drive.
USB flash drive on the CompTIA A+ exam
Core 1 objective 3.4 lists flash drives and memory cards under removable storage. Objective 3.5 ties in through boot options and USB permissions in BIOS/UEFI. Know that a flash drive is solid-state NAND storage with no moving parts, that FAT32 cannot hold files of 4 GB or larger while exFAT and NTFS can, and that flash drives are the usual installation and recovery media. Core 2 adds BitLocker To Go, USB-borne malware, and data destruction.