The performance drop most people blame on “bad cards” is usually normal behavior.

If you’ve ever had a microSD card that felt fast when it was new but frustratingly slow a year later, you’re not imagining things. This is a real, measurable behavior in flash storage, and it happens even with reputable brands. The important part is this: most of the time the card isn’t “broken.” It’s just working harder internally than it used to. In fact, real-world reporting shows reliability issues across removable flash are becoming more common, with USB flash key failures increasing by over 300% in recent years.

The slowdown usually comes from the way flash memory manages itself over time, not from sudden damage. And once you understand what’s happening inside the card, you start to see why some use cases age gracefully while others fall off a performance cliff.

A simple mental model helps.

Think of your microSD card as a warehouse

Picture your microSD card as a warehouse full of boxes. Each box represents a piece of data. The shelves are the flash memory. The warehouse manager is the controller inside the card. The manager has one annoying rule they must follow: once a box is placed on a shelf, it cannot be edited. If something changes, a new box must be placed somewhere else and the old box is marked as obsolete.

That rule isn’t a metaphor. That’s how NAND flash actually works. Flash cannot overwrite data in place. Every change becomes a new write somewhere else.

Early on, the warehouse is empty. There’s space everywhere. New boxes get placed quickly. The manager barely has to think. Performance feels fast and effortless.

Over time, more shelves fill up. Old boxes pile up. Some shelves contain a mix of useful boxes and obsolete ones. Now the manager has more work to do. They must constantly decide which shelves can be cleaned, which boxes must be moved, and where new boxes can go. That housekeeping work happens in the background, but it competes directly with your read and write requests. That’s where performance starts to slide.

The Untold Life of a microSD Card: From Silicon Wafer to Secure Erasure

From the outside, a microSD card looks boring. It is a black rectangle with a logo on top and some gold contacts on the back. You plug it in, it stores data, and as long as your photos or firmware or logs show up when you need them, you do not think about it again.

Inside, though, the lifecycle of that card is far more complicated. It begins on a mirror-polished silicon wafer, passes through a kind of semiconductor acupuncture ritual, goes through secretive factory software that “marries” the memory with its controller, and then spends the rest of its life slowly leaking electrical charge while you expect it to act like permanent storage. Sometimes it works. Sometimes it fails in the field. And sometimes it quietly forgets what you asked it to remember.

If you build products that depend on microSD cards—embedded systems, data loggers, cameras, industrial controllers, point-of-sale terminals—understanding that lifecycle is not a fun piece of trivia. It is the difference between a stable deployment and mysterious support calls six months after launch.

Where a microSD Card Really Begins

The story of a microSD card does not start in a retail box. It starts in a fabrication plant, usually owned by a NAND supplier such as Samsung, Micron, Hynix, or Toshiba/Kioxia. These facilities are some of the most controlled environments on earth. Airflow, temperature, and airborne particles are monitored more carefully than in most hospital operating rooms.

On a production line that costs billions of dollars to build, wafers are gradually constructed. Layer after layer of material is deposited, patterned with light, etched away, and doped with impurities. This is where the memory cells that eventually become your “32 GB” or “512 GB” microSD cards are physically defined. At this stage, nothing looks like a card. Everything looks like repeated patterns of tiny rectangles on a circular wafer of polished silicon.

Once the circuits are built, there is an obvious question: how much of this wafer is actually usable? That is where wafer probing comes in.

USB “Local Disk” in 2025: the XP-era hack had its moment—here’s the cleaner way (plus a product we found)

If you landed here from our old tutorial about making a USB stick look like a hard drive, you’re reading a time capsule. That guide leaned on an XP-friendly INF/registry trick (tweaking the removable bit with a modified driver). It was clever back then. On modern Windows 10/11, it’s unreliable, brittle with updates, and a magnet for driver-signing hassles. Even when you shoehorn it in, many apps and corporate policies now check the device class the hardware presents—not the label you forced with a file edit.

What changed under the hood

• Windows storage stacks matured (UASP, policy and security hardening), and driver signing isn’t casual anymore.
• Backup, imaging, and install tools increasingly verify “fixed disk” at the hardware level. A spoofed driver doesn’t pass that sniff test.
• Enterprise environments often block or restrict “removable” media regardless of what the OS UI says.

What actually works now

You start with hardware that natively enumerates as a fixed disk. No patched drivers, no post-install gymnastics. The device tells Windows, “I’m a hard drive,” and everything—from Disk Management to BitLocker to fussy installers—behaves accordingly. The brilliant bit about this method is the configuration follows the device. No more editing every PC the USB is connected to.

A product that does exactly that

We found a solution from Nexcopy called USB HDD Fixed Disk . It’s a USB flash device configured at the controller/firmware level to appear as a Fixed Disk / Local Disk on any computer. No utilities to run, no INF edits, no per-PC setup—just plug in and it registers as a hard drive.

Fuzzing is a testing method that uses automated software to feed invalid, unexpected, or random data into a computer program. The testing system then monitors the program for crashes, failed assertions, and potential memory leaks.

A research team associated with Purdue University developed a tool called USBFuzz, which pushes massive amounts of random data through a system’s USB bus. The project was created by Hui Peng and Mathias Payer of the Swiss Federal Institute of Technology.

Please don’t lose any sleep over the bugs that were discovered.

Peng and Payer identified one bug in FreeBSD, three in macOS (two resulting in unexpected reboots and one causing a system freeze), and four in Windows 8 and Windows 10, which resulted in Blue Screens of Death. The majority of issues were found in Linux systems, totaling eighteen bugs.

Windows users do not need to be concerned, as all identified Windows issues have been resolved. Of the eighteen Linux bugs, sixteen have already been corrected. Several of these were considered major security vulnerabilities.

What stands out about USBFuzz is its underlying goal of improving USB platform security through continuous testing and refinement. The project is also being released as open-source software, allowing developers to use it to strengthen their own USB products. The research team plans to release USBFuzz on GitHub later in 2020.

Came across an article today that I thought was a very good read. It’s a niche topic, but for anyone who deals with flash drives or media distribution, it’s worth checking out.

From the article:

The optical drive is nearly dead — no longer found in laptops and only rarely included in desktop PCs. As a result, the trend for distributing data has shifted toward USB flash drives instead of CDs or DVDs. Because of this shift, many companies are taking a closer look at purchasing a USB duplicator.

There are several factors to consider before spending thousands of dollars on duplication equipment. The article breaks the most important considerations into four categories. After reviewing these areas, you should have a much clearer understanding of which type of duplicator best fits your organization.

USB Duplication Speed

Speed is the first area to evaluate. This isn’t just about raw copy speed. It also includes the number of USB sockets, the user interface, and how much operational feedback is available during a copy session. Questions worth asking include:

# How many USB drives will you need to copy in a day or week?

# How large is the data load in MB or GB?

# What turnaround time is required between request and completion?

# Is printing or branding required on the USB devices?

# Do you need proof of performance via log files or reports?

Answering these questions helps define the type of USB duplicator you should be looking at: how many ports, what performance level, and what software features are necessary for your workflow.

Your Production Crew

The next step is understanding who will actually be running the equipment. Will the system be operated by non-technical staff, or by IT professionals? Does the organization need to restrict access to the system or protect the data content during the duplication process?

This often depends on how the content is delivered. A duplication company might receive physical master drives from clients, while a fulfillment operation might receive files automatically from an online ordering system or internal server.

Another consideration is scale. Will the organization deploy multiple duplicators across different geographic locations? Many global companies standardize on a single manufacturer so the workflow, training, and support experience remain consistent worldwide.

Understanding the people, environment, and operational requirements goes a long way toward narrowing the field.

Read-Only vs. Read-Write

The third category is the final state of the USB media being shipped. Should the drives be read-only, or remain read-write? By default, all standard flash drives are read-write. That introduces risk: files can be deleted, modified, or infected after distribution.

Because of this, many organizations look for USB duplicators that support creating read-only (write-protected) media. With this approach, files cannot be deleted, formatted, or altered, and malware cannot write itself onto the drive. It’s a practical safeguard for training material, software distribution, compliance data, and controlled documentation.

Nexcopy is cited in the article as a world leader in read-only flash drive duplication systems and is used as an example of the type of platform organizations evaluate for secure media production.

Read the full article here

Update:

From this article, the Raspberry Pi 4 USB-C power port was designed outside of official USB-IF specifications, making it incompatible with many USB-C chargers and power supplies. You can read more from the link above. The analysis leading to this conclusion was conducted by well-known Google engineer Benson Leung.

The Raspberry Pi is a collection of small computer boards assembled in a simplified way to form the foundation of a computer system. The Raspberry Pi (also known as RPi) was released in February 2012 in the United Kingdom. Its original intent was to provide a low-cost, simple computer platform for students to learn and develop on.

The original model became far more popular than anticipated and quickly expanded beyond its intended educational market into areas such as robotics. The platform does not include peripherals such as keyboards or mice, nor does it ship in a case. It is, quite literally, a bare-bones product.

To give you an idea of its popularity, Raspberry Pi products sold more than 19 million units from their 2012 launch through the end of fiscal year 2018. This places the Raspberry Pi among the best-selling computers in the world, albeit with limited resources. Until now.

This week, the Raspberry Pi Foundation released the Pi 4. It is an impressive upgrade. Here are the key specifications:

• A 1.5GHz quad-core 64-bit ARM Cortex-A72 CPU (~3× performance)
• 1GB, 2GB, or 4GB of LPDDR4 SDRAM
• Full-throughput Gigabit Ethernet
• Dual-band 802.11ac wireless networking
• Bluetooth 5.0
• Two USB 3.0 and two USB 2.0 ports
• Dual-monitor support at resolutions up to 4K
• VideoCore VI graphics supporting OpenGL ES 3.x
• 4Kp60 hardware HEVC video decoding
• Compatibility with earlier Raspberry Pi products

In addition to the hardware improvements, the Raspberry Pi Foundation says the new system includes an extensively modernized user interface, an updated Chromium 74 web browser, and a transition from USB micro-B to USB-C for power. The new connector supports an additional 500mA of current, ensuring a full 1.2A is available for downstream USB devices even under heavy CPU load.

The new boards are available to order now.

In the past, users have attempted running Windows on the Raspberry Pi platform, but performance was predictably slow. With this new configuration, we are curious to hear who has tried it and how it performs. Feel free to share your experience by emailing gmo @ getusb dot info.

How To Read and Write CID on SD Cards

If you are looking to read the CID number of an SD card, or extract the CID off an SD card, then you will find this article very helpful. Some also call this “reading the PSN off the SD card” or reading the product serial number off the SD card.

UPDATE (Feb 16, 2023):

We learned the company which manufactures this product now offers the ability to write the CID value as well as write protect the Secure Digital media.

Most phones and much of the software on phones will lock into the CID number of an SD card. The CID number is a unique card identifier number that is unique to the card itself. The CID number is valuable because software developers and hardware developers can lock software to the unique number of the device, thus eliminating the ability to pass along licensed software.

Reading the CID number from an SD card is not an easy task. It requires specific access codes to the index table of the memory card, and unless you know how to use the SD chipset of your card reader, chances are you won’t get the number—or at least not the correct and accurate number.

What is the CID number of an SD card?

The CID register is 16 bytes long and contains a unique card identification number. It is programmed during card manufacturing and cannot be changed by SD Card hosts. The CID number is a compilation of information about the card, such as manufacturer, date manufactured, checksum total, GB size, and more. Below is a table outlining all the items which make up the SD CID number.

So with all this said, how do you read the CID number from an SD card? As we’ve mentioned, it isn’t easy and it’s hardware based. If you do enough searching on the internet, you’ll find some home-brew code to read the CID numbers, but that’s only if you have the SD card or microSD card connected via an IDE bus to your host computer. This isn’t easy for everyone. There is clear evidence that using a USB to SD card reader will not get you the information you require—or at least accurate and correct information. Meaning most times the CID number generated is actually the serial number of the card reader itself, not the CID number of a specific SD card.

In addition, what if you are required to read the CID number off SD media in bulk? A single, one-at-a-time solution is not practical.

In my search to read the CID number from SD media, I came across Nexcopy – a manufacturer of USB duplicator equipment and other flash memory equipment. Several models they carry are SD duplicators and microSD duplicators. With the secure digital duplicators, part of their feature set includes reading CID numbers from SD media. The equipment can read 20 cards at a time, 40 cards at a time, or 60 cards at a time, depending on the model. The duplicators will read the CID number and export it to a .csv file for import into other business functions. This configuration makes it quick and easy to obtain the CID number. Granted, the equipment is not designed for single-use operation, but rather reading the CID of SD media in bulk quantity. Here is a screenshot of Nexcopy’s software reading 20 CID numbers:

I didn’t contact Nexcopy Incorporated for pricing of the equipment, but doing a quick search for the equipment shows me a price of about $1k for the smallest 20 target system and $3k for the largest 60 target system.

With all this said, there is still no clear-cut method to read CID numbers off SD cards for the home-user, but maybe this article will at least explain why you haven’t found a good solution as of yet.

The CID (Card Identification) number is a unique identifier that is assigned to each Secure Digital (SD) card. The CID number is a 16-byte value that is used by the SD card host device to identify the SD card and to determine its capabilities.