High Endurance Rugged Solution
Secure Digital was first introduced in 1999, evolving from MultiMedia Cards (MMC), primarily as a consumer-based storage medium for the photography market. This technology has been leveraged into the industrial space due to the advantages of size, low power consumption, simplicity of integration and availability. Governed by the SD Association (www.sdcard.org), the SD platform has continued to expand as capacities and bus speeds increased, while smaller form factors were developed.
The two most prevalent card formats are the full size SD and the microSD, however, understanding the different capacities, bus speeds, speed classes and associated compatibility with host devices is critical to successfully implementing the SD interface.
SD and microSD cards are marked as SD, SDHC or SDXC – which is a capacity-related classification – as detailed in the table below:
|SD Standard||SDHC Standard||SDXC Standard|
|Capacity||up to 2GB||more than 2GB||more than 32GB|
|up to 32GB||up to 2TB|
|File System||FAT 16||FAT 32||exFAT|
|SD Memory Cards / Host Marking|
|Card form factor||Full Size SD||32 x 24 x 2.1 mm, Approximately 2g|
|microSD||11 x 15 x 1.0 mm, Approximately 0.5g|
|Bus Speed||Normal Speed (NS)||NS, HS||NS, HS|
|High Speed (HS)||UHS-I||UHS-I|
|Speed Classes||NS, HS mode||Speed Class (optional)||Speed Class (Mandatory)||Speed Class (Mandatory)|
|UHS-I mode||----||Speed Class (Optional)|
UHS Speed Class (Optional)
|Speed Class (Optional)
UHS Speed Class (Optional)
Cards are only compatible with hosts that are rated for the same capacity grade or higher, for example, SDHC cards are only compatible with SDHC or SDXC hosts, not SD hosts, as illustrated in the graphic below.
The second classification of cards is related to the bus interface, designated as Normal Speed, High Speed, UHS-I (Ultra High Speed) or UHS-II, which are differentiated by the Bus Speed. Bus Speed indicates the maximum theoretical read & write speed for a card, however the actual performance is affected by many other factors, such as the card configuration, operation being performed, organization of data on the card, etc. The UHS Bus Interfaces are only applicable to SDHC and SDXC capacity grades, and while UHS memory cards can be used in non-UHS hosts, the performance will always be best in a UHS host.
|Bus Interface||Card Type||Bus Mark||Bus Speed||Spec Version|
|Normal Speed||SD, SDHC and SDXC||---||12.5MB/s||1.01|
|High Speed||SD, SDHC and SDXC||---||25MB/s||2|
|UHS-I||SDHC and SDXC||50MB/s (SDR50, DDR50)|
|UHS-II||SDHC and SDXC||156MB/s|
Speed class ratings indicate the minimum sustained write speed of a given card, originally developed for video recording. Normal Speed bus interfaces utilize a Class 2, 4, or 6 system to indicate that the card will record a minimum of 2 MB/s, 4 MB/s or 6 MB/s, respectively. High Speed bus interface supports Class 10 speed class, indicating 10 MB/s minimum write speed.
UHS speed classes are a completely different set of write performance ratings for UHS devices when used in UHS hosts. UHS Speed Class 1 (U1) indicates a minimum write speed of 10 MB/s, whereas UHS Speed Class 3 (U3) indicates a 30 MB/s minimum write speed, specifically targeted for 4K video recording.
Delkin offers full size SD and microSD cards in a range of capacities, bus speeds and speed class ratings, as well as multiple flash configurations, to allow selection of the optimum card for the host and usage model.
SD / SDHC / SDXC
Delkin Devices’ full-size SD cards utilize a true industrial controller and SLC flash to deliver a rugged, high endurance solution for applications that are write intensive, subject to extreme environmental conditions or which require long term field reliability when recording mission critical data.
Utility SD / microSD
Delkin Devices developed the Utility concept for OEM’s and embedded designers that need a cost-effective, yet controlled storage solution. In many cases, the cost of the host and the usage model does not support the use of high-endurance SLC flash, yet the application still requires an industrial-grade product, consistent performance and life cycle management.