MicroSD cards, sometimes referred to as TransFlash or TF cards, are a popular type of removable flash memory card used for storage in portable devices such as mobile phones, tablets, and digital cameras. There are several formats that microSD cards adhere to, with the most common being the microSD standard. This article will provide an overview of the microSD format, its history, technical specifications, and usage in consumer devices.
History of MicroSD
The microSD format was originally created in 2005 by the SD Association (SDA), an organization that develops and promotes memory card standards. It was designed as a smaller variant of the SD card format, using the same underlying technology but reduced in physical size for use in smaller portable devices. The SDA released the microSD specification along with the microSDHC specification for higher capacity cards up to 32GB. Over the years, further enhancements have been made to increase maximum capacities and improve transfer speeds.
Some key milestones in the history of microSD include:
- 2005 – Original microSD format released, supporting cards up to 2GB
- 2006 – microSDHC released, supporting 4-32GB capacities
- 2009 – microSDXC announced, supporting up to 2TB eventual capacity
- 2011 – UHS-I interface added, enabling up to 104MB/s transfer speeds
- 2016 – UHS-III interface added, enabling up to 624MB/s transfer speeds
As of 2022, the latest microSD standard supports cards up to 1TB and UHS-I speed classes up to A2 for better performance in applications like 4K video recording and gaming.
MicroSD Technical Specifications
MicroSD cards utilize flash memory and conform to a specific set of technical standards managed by the SD Association. Here are some key technical details:
- Physical size – 15mm x 11mm x 1mm (microSD), 15mm x 11mm x 0.7mm (microSDHC/XC)
- Interface – SD bus interface, supports UHS-I and UHS-III
- Capacity – Up to 1TB currently; theoretical limit of 2TB
- Speed class – UHS speed class rating from U1 up to A2 for faster performance
- Durability – Waterproof, shockproof, X-ray proof, magnet proof
- Security – Optional digital rights management (DRM) and SD-protect features
MicroSD uses a 9-pin interface that includes power, ground, clock, command, and 4 data pins. The interface supports a proprietary SD protocol running on top of the physical layer. Speed classes like UHS-I define interface timing and speed parameters to ensure compatibility across devices.
MicroSD Capacities
MicroSD cards are available in a wide range of storage capacities to suit different purposes. Some common capacities include:
- 16GB
- 32GB
- 64GB
- 128GB
- 256GB
- 512GB
- 1TB
Higher capacity cards are ideal for storing more photos, videos, music, and apps. A 1TB microSD can hold up to 40 hours of 4K video footage. Lower capacity cards like 16-32GB may be more cost effective for basic usage in applications like fitness trackers.
MicroSD Speed Classes
MicroSD cards have speed class ratings that indicate their minimum guaranteed performance, shown as a number inside a C or A with a U symbol. Here are the different speed classes:
| Speed Class | Minimum Speed |
|---|---|
| U1 | 10MB/s sequential read |
| U3 | 30MB/s sequential read |
| A1 | 10MB/s random read IOPS |
| A2 | 4000 random read/2000 random write IOPS |
Cards with higher speed ratings like U3 or A2 provide better performance for photo burst shooting, 4K video recording, gaming, and running apps from the memory card. However, they also have higher cost per GB compared to slower cards.
Uses of MicroSD
Due to their tiny physical footprint, high storage capacity, and removability, microSD cards are very commonly used as external storage in the following types of devices:
- Smartphones – For storing photos, videos, downloads
- Tablets – Storage expansion for apps, media, documents
- Action cameras – Dashcams, bodycams, drones
- Handheld gaming – Nintendo Switch, Steam Deck
- Drones – Storing aerial footage
MicroSD is popular because it allows adding more storage conveniently and cheaply after purchase, without needing to buy a model with more built-in storage. The cards can also be reused across different devices.
Other MicroSD Uses
Beyond portable consumer devices, microSD has some other common uses including:
- Raspberry Pi single-board computers
- Dash cams and security cameras
- Wearable devices like fitness bands
- IoT smart home devices
Its tiny size makes it well suited for integrating removable storage into very compact devices where even miniSD would be too bulky.
Conclusion
MicroSD is the most ubiquitous format of removable flash storage used in smartphones, cameras, handheld gaming devices, and many other compact gadgets. The standard was created in 2005 and has evolved over time to support capacities up to 1TB and interface speeds up to 624MB/s. MicroSD cards utilize NAND flash memory chips encased in a durable physical shell that is extremely compact – just 15mm x 11mm in size. Key characteristics include waterproofing, shock resistance, and flexibility to use across different devices via the removability. Speed classes help ensure a minimum level of performance, while microSD remains highly cost effective in terms of storage capacity per dollar compared to other formats.
