Types of SD Cards
There are currently 4 different SD card standards that deal with storage capacity. SD stands for Secure Digital and the standards are controlled by the SD Association.
There are multiple ratings and standards that deal with the transfer speed of SD cards. These are important to pay attension to if you want to record video.
SD cards are avialable in 2 different physical sizes. The “standard” size and microSD.
What are the Physical Dimensions of SD Cards?
The dimensions of standard SD cards are approximately 32 mm × 24 mm × 2.1 mm.
MicroSD cards have dimensions of approximately 15 mm × 11 mm × 1 mm.
MicroSD Card Adapters
MicroSD card adapters are small plastic or metal devices that allow you to use a MicroSD card in an SD card slot. They have the same rectangular shape as an SD card, but are thinner and have a smaller slot in which to insert the MicroSD card.
The adapter allows the MicroSD card to fit securely into an SD card slot, so that it can be used in devices that are not compatible with MicroSD cards.
MicroSD card adapters are often included with MicroSD cards, but can also be purchased separately if needed.
What are the SD Card Standards for Storage?
These are the four different SD card standards for capacity:
| SD Card Type | Storage Capacity Range | File System |
|---|---|---|
| SDSC (Standard Capacity) | Up to 2GB | FAT12 and FAT16 |
| SDHC (High Capacity) | 2GB to 32GB | FAT32 |
| SDXC (Extended Capacity) | 32GB to 2TB | exFAT |
| SDUC (Ultra Capacity) | 2TB to 128TB | exFAT |
exFAT is commonly used in a variety of storage devices in addition to SDXC and SDUC cards.
Camera Compatibility Problems
When trying to use an SD card that has a storage capacity that is larger than what is supported by a camera, there are several compatibility problems that can occur:
- Card not recognized: The camera may not recognize the SD card at all, preventing you from using it to store photos or videos.
- Limited storage: Even if the camera recognizes the card, it may only be able to use a limited portion of its storage capacity. For example, a camera that supports SDHC cards may only be able to use up to 32GB of an SDXC card’s capacity, leaving the remaining space unused.
- Reduced performance: Using an SD card that is too large for a camera can also result in reduced performance, as the camera may not be able to write data to the card as quickly as it would with a smaller card. This can lead to slower save times and decreased overall performance.
- Data corruption: In some cases, using an SD card that is too large for a camera can lead to data corruption or loss. This can occur if the camera is unable to properly read or write data to the card, or if there are compatibility issues between the card and the camera’s firmware.
To avoid these compatibility problems, check the camera’s manual, or look for information on the battery door/SD card slot door. There may be icons showing camera compatibility.
SDSC - Standard Capacity
SDSC (Standard Capacity) SD cards are the earliest and smallest type of SD cards, with a maximum storage capacity of 2GB. They were introduced in 1999 and were commonly used in digital cameras, portable music players, and other electronic devices.
SDSC cards use the FAT12 or FAT16 file system and have a data transfer rate of up to 12.5 MB/s. They have a physical size of 32mm x 24mm x 2.1mm (1.26 inches x 0.94 inches x 0.08 inches) and typically have a write-protect switch on the side that allows users to prevent data from being overwritten or deleted accidentally.
SDHC - High Capacity
SDHC (High Capacity) SD cards are a type of SD card that can store more data than their SDSC predecessors, with a storage capacity of up to 32GB. They were introduced in 2006 to accommodate the growing storage needs of digital cameras and other portable devices.
SDHC cards use the FAT32 file system and have a data transfer rate of up to 25 MB/s. They have the same physical size as SDSC cards, at 32mm x 24mm x 2.1mm (1.26 inches x 0.94 inches x 0.08 inches), but have a different logo on the card to distinguish them from SDSC cards.
SDHC cards are backwards compatible with devices that support SDSC cards, but may not be compatible with older devices that only support the FAT16 file system. To ensure compatibility, it’s important to check the specifications of your device to determine which types of SD cards it supports.
SDXC - Extended Capacity
SDXC (eXtended Capacity) SD cards are a type of SD card that offer even higher storage capacities than SDHC cards, with a maximum capacity of up to 2TB (although currently not available at that size). They were introduced in 2009 to meet the increasing demand for larger storage capacities in portable devices.
SDXC cards use the exFAT file system, which allows for larger file sizes than the FAT32 file system used by SDHC cards. They have a data transfer rate of up to 104 MB/s, which is much faster than the transfer rate of SDHC cards.
SDXC cards are backwards compatible with devices that support SDHC and SDSC cards, but may not be compatible with older devices that only support the FAT32 file system. As with SDHC cards, it’s important to check the specifications of your device to determine which types of SD cards it supports.
SDUC - Ultra Capacity
SDUC (Ultra Capacity) SD cards are a type of SD card that offer even higher storage capacities than SDXC cards, with a maximum capacity of up to 128TB. None are currently commercially available.
SDUC cards use the exFAT file system, like SDXC cards, and have a data transfer rate of up to 985 MB/s, which is much faster than the transfer rate of SDXC cards.
The Different SD Card Speed Classes
There are several different standards used to indicate the transfer speed of SD cards. These standards are defined by the SD Association and are typically marked on the card with a number followed by the letter “MB/s”. Here are the different standards used to indicate the transfer speed of SD cards:
- Speed Class: As I mentioned earlier, Speed Class is a standard that indicates the minimum sustained write speed of the card. The different Speed Classes are Class 2, Class 4, Class 6, Class 10, UHS Speed Class 1 (U1), and UHS Speed Class 3 (U3).
- Ultra High Speed (UHS) Bus Interface: This is a newer standard that indicates the maximum bus interface speed of the card. There are two different UHS bus interfaces: UHS-I and UHS-II. UHS-I cards have a maximum bus interface speed of 104 MB/s, while UHS-II cards have a maximum bus interface speed of 312 MB/s.
- Video Speed Class: This is a newer standard that indicates the minimum sustained write speed of the card for video recording. The different Video Speed Classes are V6, V10, V30, V60, and V90, with V6 indicating a minimum sustained write speed of 6 MB/s and V90 indicating a minimum sustained write speed of 90 MB/s.
It’s important to note that the transfer speed of an SD card is not just determined by its class or standard, but also by factors such as the device it’s used in and the type of file being transferred.
Speed Ratings: Megabytes vs. Megabits
Megabytes (MB) and Megabits (Mb) are both units of measurement used to describe digital storage and transfer speeds, but they represent different things.
A byte is a unit of data storage that contains eight bits. In contrast, a bit is the smallest unit of digital information and represents a single 0 or 1. When discussing data transfer rates, Megabytes per second (MB/s) refers to the number of bytes transferred in one second, while Megabits per second (Mb/s) refers to the number of bits transferred in one second.
Because a byte is composed of eight bits, a transfer rate of 1 MB/s is equal to 8 Mb/s. When comparing transfer speeds, Mbps values will typically be higher than MB/s values for the same transfer rate. For example, a transfer speed of 100 MB/s is equivalent to 800 Mb/s.
When discussing storage capacity, the same principle applies. A byte is composed of eight bits, so 1 Megabyte (MB) is equal to 8 Megabits (Mb). This means that a device with a storage capacity of 16 GB can hold 16,000 Megabytes (MB) or 128,000 Megabits (Mb).
It’s important to keep this distinction in mind when comparing transfer speeds or storage capacity. Mbps is typically used for describing network transfer speeds, while MB/s is more commonly used for storage transfer speeds.
SD Card Speed Class
The SD Card Speed Class is a standard that indicates the minimum sustained write speed of the card. This is an important factor to consider when using SD cards for tasks such as video recording, where a slow write speed can result in dropped frames or other issues.
Here is a table of transfer speeds for each Speed Class:
| Speed Class | Minimum Sustained Write Speed | Transfer Speed (MB/s) |
|---|---|---|
| Class 2 | 2 MB/s | Up to 2 |
| Class 4 | 4 MB/s | Up to 4 |
| Class 6 | 6 MB/s | Up to 6 |
| Class 10 | 10 MB/s | Up to 10 |
UHS - Ultra High Speed
UHS stands for Ultra High Speed, which is a newer standard for SD cards that offers higher transfer speeds than the previous Speed Class standard. UHS is backward compatible with previous Speed Class standards, but requires a UHS-compatible device to take full advantage of its higher transfer speeds.
There are three versions of the UHS standard: UHS-I, UHS-II, and UHS-III. UHS-I cards have a maximum bus interface speed of 104 MB/s, while UHS-II cards have a maximum bus interface speed of 312 MB/s, and UHS-I cards have a maximum bus interface speed of 104 MB/s.
| UHS Standard | Transfer Speed (MB/s) |
|---|---|
| UHS-I | 104 MB/s |
| UHS-II | 312 MB/s |
| UHS-III | 624 MB/s |
Video Speed Class
The Video Speed Class (VSC) is a standard used to indicate the minimum sustained write speed required for video recording. The VSC rating is represented by a number inside a letter V, such as V30 or V60. The following table shows the transfer speeds and minimum sustained write speeds for each VSC rating:
| VSC Rating | Minimum Sustained Write Speed | Bus Speed |
|---|---|---|
| V6 | 6 MB/s | UHS-I |
| V10 | 10 MB/s | UHS-I |
| V30 | 30 MB/s | UHS-I |
| V60 | 60 MB/s | UHS-II |
| V90 | 90 MB/s | UHS-II |
| V120 | 120 MB/s | UHS-II |
It is important to note that the VSC rating indicates the minimum sustained write speed, which means that the card should be able to maintain that speed for the duration of the video recording. If the card does not have a fast enough write speed, the recording could suddenly end or be corrupted.
SD Express
The SD Express standard combines the existing SD interface with PCIe and NVMe interfaces to provide faster data transfer speeds. This standard can achieve speeds of up to 985 MB/s using PCIe Gen3 x1 lanes, and up to 3.94 GB/s using PCIe Gen4 x4 lanes. The SD Express cards are available in both SDHC and SDXC form factors.
The number of PCIe lanes used by the SD Express card determines the maximum data transfer speed. Here’s a table of the maximum transfer speeds based on the number of PCIe lanes used:
| Transfer Speed | PCIe Lanes | Version |
|---|---|---|
| 985 MB/s | 3.1 x1 | 7.0 |
| 1969 MB/s | 3.1 x2 | 8.0 |
| 3938 MB/s | 4.0 x1 | 8.0 |
| 7876 MB/s | 4.0 x2 | 8.0 |
SD Express cards are backward compatible with SD UHS-I, UHS-II, and UHS-III host devices, but they require an SD Express compatible host device to achieve the maximum transfer speeds.
microSD Express
MicroSD Express is a standard for microSD cards that was finalized in 2019 by the SD Association. It combines the high-speed PCIe interface with the widely used microSD form factor, allowing for much faster data transfer rates than previous microSD cards.
The MicroSD Express standard supports PCIe 3.1 and NVMe 1.3 protocols, which can achieve data transfer speeds of up to 985 MB/s. It also features backward compatibility with the UHS-I interface for compatibility with older devices.
SD Cards with Integrated Wifi
WiFi enabled SD cards, also known as “wireless” or “smart” SD cards, are standard SD cards with built-in WiFi connectivity, allowing users to wirelessly transfer photos and videos to a computer or mobile device without the need for a separate card reader. They work by creating their own ad-hoc WiFi network, which a device can connect to using an app or web browser.
WiFi enabled SD cards are particularly useful for photographers who need to quickly transfer images from their camera to a device for editing or sharing, as well as for people who want to backup their photos to the cloud or a remote storage device without having to physically connect their camera or SD card to a computer. Some WiFi enabled SD cards also offer additional features such as automatic backup, geotagging, and remote control of a camera.
These cards have fallen out of favor now that all cameras are being released with Wifi, bluetooth, and other connection options.
Here is a list of some SD cards that contain built-in Wi-Fi:
- Eye-Fi Mobi Pro
- Toshiba FlashAir
- Transcend Wi-Fi SD
- PQI Air Card
- EZ Share Wi-Fi SD Card
- Delkin Wi-Fi SD Card
- Sandisk Connect Wireless SD Card
- Kingston Wi-Drive Wireless Storage Solution
- Trek Flucard Pro SD
- Sony SF-G series Wi-Fi SD Card
How to Recover Data from an SD Card
Data recovery from an SD card can be done using specialized software designed for this purpose. There are many such software applications available for purchase or download.
The basic process of data recovery involves connecting the SD card to a computer using a card reader or USB adapter, and then using the recovery software to scan the card for recoverable data. The software may allow for a quick scan or a deep scan, depending on the level of corruption or damage to the SD card.
Once the scan is complete, the software will present a list of recoverable files that can be saved to another location on the computer or an external drive. It’s important to save the recovered files to a different drive or location than the original SD card to avoid overwriting any remaining data that may still be recoverable.
In some cases, data recovery may not be possible if the SD card is physically damaged beyond repair or if the data has been overwritten. It’s always recommended to regularly backup important data to avoid the need for data recovery in the first place.