What is an SD Card? Specifications and Types
Given the widespread use of memory cards in our daily lives, various manufacturers have introduced different specifications of memory cards for different applications. However, the plethora of specifications has left many consumers confused. This article aims to provide a comprehensive explanation of memory cards to help you select the right one for your needs.
The full name for an SD card is Secure Digital Memory Card, abbreviated as “SD.” It is a new generation of memory devices based on semiconductor flash memory. Developed jointly by Panasonic, SanDisk, and Toshiba in 1998 and 1999, the SD card is a small storage medium. In 2000, these companies established the Secure Digital Association (SDA) to set SD card standards.
What is a TF Card? What is a microSD Card?
The full name of a TF card is TransFlash Card, which is a smaller storage card designed using SD architecture. It is about the size of an adult fingernail, measuring 11mm x 15mm x 1.4mm, roughly a quarter of the size of a standard SD card. Introduced by SanDisk and Motorola in 2004, the TF card was later adopted by the SDA and renamed microSD card. Thus, terms like T card, TF card, and microSD card all refer to the same type of micro memory card.
Various Types of SD Card Products
The table below details the different types of SD card products, highlighting their specifications, dimensions, and application features.
Product Type | Image | Description / Dimensions | Application / Features |
---|---|---|---|
SD 3.0 and below |
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9 pins, currently the most common SD card, UHS-I transfer speed up to 104MB/s. 32mm x 24mm x 2.1mm | Cameras, car DVRs |
microSD 3.0 and below |
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8 pins, currently the most common microSD card, UHS-I transfer speed up to 104MB/s. 15mm x 11mm x 0.7mm (1.0mm tail thickness) | Phones, dash cams, surveillance |
SD 4.0 |
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17 pins, UHS-II transfer speed up to 312MB/s, first row pins compatible with SD 3.0 and below. 32mm x 24mm x 2.1mm | UHS-II high performance supports 4K, 8K, and 3D video recording |
microSD 4.0 |
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16 pins, UHS-II transfer speed up to 312MB/s, first row pins compatible with microSD 3.0 and below. 15mm x 11mm x 0.7mm (1.0mm tail thickness) | UHS-II high performance supports 4K, 8K, and 3D video recording |
Half SD 4.0 |
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Half the length of an SD 4.0 card, but otherwise identical. 21mm x 24mm | Supports 4K, 8K, and 3D video recording, suitable for Surface Book storage and space upgrades |
UFS Card (Universal Flash Storage Card) |
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Released in March 2016, UFS 1.0 spec with transfer bandwidth up to 5836.3 Mbps, similar in size to microSD. 11mm x 15mm | Currently incompatible with SD slots; potential future dual-slot designs may support both microSD and UFS cards. Expected to first appear in Samsung phones. |
By understanding these various types of SD card products, consumers can make informed decisions when selecting the right memory card for their specific needs.
The Relationship and Differences Between microSD and SD Cards
A microSD card is a smaller version of an SD card, and technically, they are fundamentally the same as both follow the SD protocol. The main difference lies in their physical form.
A microSD card can be converted into an SD card using an adapter. This adapter essentially houses the microSD card and transforms it so that it matches the shape and functionality of a standard SD card. The adapter contains the necessary wiring to convert the microSD card’s pin configuration to that of an SD card.
A microSD card has 8 pins, while an SD card has 9 pins. The additional pin in SD cards is because SD cards have two ground (GND) pins.
The Relationship and Differences Between microSD and SD Cards
A microSD card is a smaller version of an SD card, and technically, they are fundamentally the same as both follow the SD protocol. The main difference lies in their physical form.
A microSD card can be converted into an SD card using an adapter. This adapter essentially houses the microSD card and transforms it so that it matches the shape and functionality of a standard SD card. The adapter contains the necessary wiring to convert the microSD card’s pin configuration to that of an SD card.
A microSD card has 8 pins, while an SD card has 9 pins. The additional pin in SD cards is because SD cards have two ground (GND) pins.
Why is Actual Capacity Smaller Than the Standard Capacity?
This discrepancy arises mainly due to different calculation methods used by flash memory manufacturers and computer systems. Flash memory manufacturers calculate storage capacity using 1GB = 1000MB, 1MB = 1000KB, etc. However, computer systems calculate it as 1GB = 1024MB, 1MB = 1024KB, etc. Additionally, SD card firmware occupies some space, usually not very large. Typically, the actual capacity of an SD card read by a computer is about 90% to 93% of the standard capacity.
How Does the Write-Protect Switch on an SD Card Work? Is the Card Always Write-Protected When Locked?
The write-protect switch on an SD card is simple in its operation. It does not affect the internal circuitry of the SD card. The write-protection is controlled by the circuitry in the external card reader. When the write-protect switch is in the “Unlock” (open) position, the metal clip in the card reader is in contact, allowing data to be written to the SD card. When the switch is in the “Lock” (closed) position, the clip is disengaged, preventing data from being written. Therefore, the effectiveness of the write-protect switch depends on whether the card reader is designed with this function.
What Are SD1.0, SD2.0, SD3.0, and SD4.0 Cards?
The SD Association has introduced various specification protocols for SD cards, such as SD1.0, SD2.0, SD3.0, and SD4.0. Each version complies with the corresponding standards set by the SD Association, with differences mainly in capacity and bus speed. The table below summarizes the supported bus modes for each SPEC version:
Bus Interface Table
Bus Interface | Card Type | Bus Marking | Bus Speed | Specification Version |
---|---|---|---|---|
Default Speed | SD, SDHC, and SDXC | … | 12.5MB/s | 1.01 |
High Speed | SD, SDHC, and SDXC | … | 25MB/s | 1.10 |
UHS-I | SDHC and SDXC | ![]() |
50MB/s (SDR50, DDR50), 104MB/s (SDR104) | 3.01 |
UHS-II | SDHC and SDXC | ![]() |
156MB/s Full Duplex, 312MB/s Half Duplex | 4.00 |
UHS-III | SDHC and SDXC | ![]() |
312MB/s Full Duplex, 624MB/s Full Duplex | 6.00 |
- SD1.0: Normal Speed bus interface, maximum bandwidth 12.5MB/s, no unified speed (read/write) marking on the card.
- SD2.0: Up to 32GB capacity, High Speed bus interface, maximum transfer bandwidth 25MB/s, card has Class rating markings.
- SD3.0: Ultra High Speed I (UHS-I) bus interface, bus speed up to 104MB/s (SDR104 mode).
- SD4.0: Ultra High Speed II (UHS-II) bus interface, transfer rates up to 312MB/s. UHS-II cards have additional pins on the physical interface.
- UHS-III: Ultra High Speed III, new SD6.0 standard, same physical pin layout as UHS-II, bandwidth up to 624MB/s.
SD Card Speed Classes
SD card speed classes are divided into various categories. The table below details these classifications.
Speed Class Table
Speed Class | Class Levels | Bus Mode | Speed |
---|---|---|---|
Speed Class | Class 4, Class 6, Class 10 | HS | Sequential write speed of 4MB/s, 6MB/s, 10MB/s or higher |
UHS Speed Class | U1, U3 | UHS-I, UHS-II | Sequential write speed of 10MB/s, 30MB/s or higher |
Video Speed Class | V6, V10 | HS, UHS-I, UHS-II | Sequential write speed of 6MB/s, 10MB/s |
V30 | UHS-I, UHS-II | Sequential write speed of 30MB/s | |
V60, V90 | UHS-II | Sequential write speed of 60MB/s, 90MB/s | |
Application Performance Class | A1 | UHS-I (“DDR50”, “SDR50”, “SDR104”), UHS-II | Minimum 4K random read/write 1500/500 IOPS; minimum sustained sequential write performance 10MB/s |
A2 | UHS-I (“DDR50”, “SDR50”, “SDR104”), UHS-II | Minimum 4K random read/write 4000/2000 IOPS; minimum sustained sequential write performance 10MB/s |
Difference Between Class 10 and U1
Class 10 and U1 both have write speeds of 10MB/s or higher, but they are distinct standards. Speed Class (e.g., Class 10) is defined under SD2.0 mode, while UHS Speed Class (e.g., U1) is defined under SD3.0 UHS mode. Because they are independent of each other, many memory cards are marked with both U1 and C10 to indicate they meet both standards.
The Meaning of SDSC, SDHC, and SDXC
SDSC, SDHC, and SDXC have different meanings and specifications as outlined below.
SDSC, SDHC, and SDXC Table
Standard | Capacity | File System | SD Logo |
---|---|---|---|
SDSC | Up to 2GB | FAT12, FAT16 | |
SDHC | More than 2GB, up to 32GB | FAT32 | |
SDXC | More than 32GB, up to 2TB | exFAT |
Do SDSC, SDHC, and SDXC Relate to Speed? Is SDXC Faster than SDHC?
SDSC, SDHC, and SDXC are classified based on card capacity and are not directly related to the speed of the SD card. The speed of an SD card depends on the quality of the flash memory and the design of the solution. Therefore, an SDXC card is not necessarily faster than an SDHC card.
Is an SDXC Card an SD3.0 Card?
An SDXC card does not necessarily indicate it is an SD3.0 card. SDXC only refers to capacity, which ranges from 32GB to 2TB, and does not correlate directly with the SD version. For instance, a 64GB (SDXC) SD card can be produced in SD2.0 mode.
When Does a Card’s Speed Decrease?
An SD card’s read/write speed may slow down after extensive use due to an increase in “dirty” data or garbage data, which requires more time for the controller to perform garbage collection.
Long-term disuse of an SD card can also lead to slower speeds. Due to the characteristics of NAND flash memory, long-term storage can cause data corruption due to electron leakage and crosstalk. The controller may need to perform multiple read retries, which significantly impacts read/write speed.
Understanding these details helps consumers choose the right type of memory card for their needs.
Conclusion
Choosing the right SD card can significantly impact the performance and efficiency of your devices. Main brands like SanDisk, Kingston, and Samsung offer a variety of options tailored to different needs. Explore our selection of these trusted brands on our website to find the perfect SD card for your device, ensuring optimal performance and reliability. Investing in the right SD card ensures optimal performance for your cameras, smartphones, and other devices, enhancing your digital experience.
Upgrade Your Storage Today!
Are you ready to enhance your digital experience? Discover our extensive range of SD cards, from SDSC to SDXC, and find the perfect solution for your device. Visit our website now to explore our collection and elevate your storage capabilities. Don’t miss out on the opportunity to improve your device’s performance—shop with us today! For more insights and the latest updates on memory card technology, be sure to check out our blog.