Written on March 18, 2025

Object: USB Flash Drive 

Goal: Explain what it is and how it works. 

Definition 

A USB flash drive (aka USB stick, memory stick, thumb drive, and pen drive) is a small, portable device that allows for data transfer and storage in flash memory. It is designed to be compatible with any device (desktops, PCs, projectors, 3D-printers, etc.) that has a USB port in a “plug and play” fashion i.e. it functions without any explicit configuration from the user. 

Function 

USB flash drives primarily function as portable storage devices capable of persisting all forms of digital data such as documents, images, videos, software, and operating systems. Storage capacity varies widely across USB flash drives, typically ranging from 2-64 GB, with some designed to hold up to 4 TB of data. While they can theoretically store any type of data, specific USB flash drives are limited by their storage capacity and formatting. The format of a USB flash drive is the file system it uses to organize its data. 

Corollary functions include: 

1. Quick data transfer between devices (e.g. porting a 3D model to a 3D printer, copying a presentation to a projector) 
2. Media sharing (e.g. sharing large video files with a friend) 
3. Portable backup (e.g. saving important documents from a PC to protect against data loss if the computer gets damaged) 
4. Boot media (e.g. a USB flash drive that allows a Windows computer to boot into an Ubuntu OS stored on the drive instead of the Windows OS stored on the computer’s own hard drive) 

Overview 

A prototypical USB flash drive is around the size of a thumb, lightweight and rectangular.  The main materials used are plastic for the outer cover, metal for the USB plug, and silicon for the internal flash memory and controller.  

There are no limits on USB flash drive appearance as long as the device contains the essential components that allow it to function. Because of this, USB flash drives can be made from unconventional materials like wood or completely custom designed. 

Components 

1	USB Plug (USB-A)
2	Mass Storage Controller Chip
4	NAND Flash Memory Chip
5	Crystal Oscillator
6	LED (Optional)
7	Write-protect switch (Optional)
8	Extra space for more memory

USB Plug (aka USB connector) 

A metal piece that plugs into USB ports on another device. Because of its shape it is also referred to as a male plug. To ensure reliable connectivity, USB plugs are made from a durable material such as stainless steel. There are two USB plug types: USB-A and USB-C.  

USB-A plugs are wider, rectangular, and unidirectional, meaning the orientation they are plugged into a device matters, i.e. it may require being flipping to be in the proper orientation. USB-C plugs are smaller, slightly rounded, and reversible. While USB-A is still used, it is a legacy standard and is gradually being replaced by the faster, more versatile USB-C.  

NAND Flash Memory Chip 

Where a USB flash drive’s data is stored. The memory chip is non-volatile, retaining its data even without power, and supports fast read and write operations.  

Mass Storage Controller Chip 

A microcontroller with software that determines how data storage, reading, and writing operations are performed. It manages data transfer between the device a USB flash drive is plugged into and the drive’s memory.  

Crystal Oscillator 

Provides the rhythm or “clock” to which data transfer operations are performed, ensuring stable and accurate digital information transfer between device and USB flash drive. 

PCB (printed circuit board) 

Connects the USB plug, mass storage controller chip, and NAND flash memory chips together allowing data (in the form of electrical signals) to pass through the USB flash drive. The PCB is typically green but can be other colors. The one in the above diagram is red. 

Case 

A plastic or metal enclosure that protects all the internal components of a USB flash drive from damage, dust, and moisture.  

Optional components 

• LED Indicator: an LED light that indicate when a USB flash drive is in use.  
• Write-protect switch: a switch that prevents write access to the NAND flash memory chip 
• Attachment point: a hole on the case that can hold a ring for attaching USB flash drives to keychains 
• Extra space: a location that can hold more NAND flash memory to increase the device’s storage capacity 
• Plug cover: a plastic, wooden, or custom designed piece that fits over the USB plug to protect it 

Explanation 

The components of a USB flash drive work together to enable data transfer and storage from a device to the drive and from the drive to a device. 

To transfer data to a USB flash drive or view and modify existing data on it: 

1. Plug a USB flash drive into a device by fitting its USB-A or USB-C plug into the device’s USB port.  
2. Wait for the device to recognize the USB flash drive. 
3. *View the USB flash drive’s contents on the device. 
4. *Transfer data from the device to the USB flash drive or from the USB flash drive to the device by dragging and dropping files. 
5. *Modify the data (create, rename, delete, move) stored on the USB flash drive using the device’s interface. 
6. Eject the USB flash drive from the device. 
7. Remove the USB plug from the USB port. 

*Read, write, and modification operations involve data flow from the device to USB plug, controller chip, and NAND memory chip (and vice versa) timed by the crystal oscillator. 

[link to demo video?] 

Conclusion  

USB flash drives are compact and lightweight, making them easy to carry around. They are designed to be durable and resistant to damage from physical shock, drops, and vibrations since they do not have any mechanical, moving parts. They can hold any type of digital data and support a wide range of storage capacities. Modern USB flash drives use fast data transfer protocols. 

While USB flash drives possess many benefits, they also have a few drawbacks. USB flash drives eventually wear out after repeated write/erase cycles. However, they can handle tens of thousands of cycles before that occurs. Because they are small, they are easy to misplace or lose. And while they are designed to endure wear and tear, they can still be physically damaged if crushed, bent, or exposed to water. Older USB flash drives are slower than the newest ones. Lastly, most USB drives lack built-in encryption, meaning anyone with the USB flash drive can access and modify its data.