Comparison To Other Flash Memory Formats
Overall, SD is less open than CompactFlash or USB flash memory drives. Those open standards can be implemented without paying for licensing, royalties, or documentation. (CompactFlash and USB flash drives may require licensing fees for the use of the SDA's trademarked logos.)
However, SD is much more open than Memory Stick, for which no public documentation nor any documented legacy implementation is available. All SD cards can be accessed freely using the well-documented SPI bus.
xD cards are simply 18-pin NAND flash chips in a special package and support the standard command set for raw NAND flash access. Although the raw hardware interface to xD cards is well understood, the layout of its memory contents—necessary for interoperability with xD card readers and digital cameras—is totally undocumented. The consortium that licenses xD cards has not released any technical information to the public.
Comparison of technical features of MMC and SD card variants| Type | MMC | RS-MMC | MMC Plus | SecureMMC | SDIO | SD | miniSD | microSD |
|---|---|---|---|---|---|---|---|---|
| SD Socket | Yes | Extender | Yes | Yes | Yes | Yes | Adapter | Adapter |
| Pins | 7 | 7 | 13 | 7 | 9 | 9 | 11 | 8 |
| Width | 24 mm | 24 mm | 24 mm | 24 mm | 24 mm | 24 mm | 20 mm | 11 mm |
| Length | 32 mm | 18 mm | 32 mm | 32 mm | 32 mm+ | 32 mm | 21.5 mm | 15 mm |
| Thickness | 1.4 mm | 1.4 mm | 1.4 mm | 1.4 mm | 2.1 mm | 2.1 mm (most) 1.4 mm (rare) |
1.4 mm | 1 mm |
| SPI mode | Optional | Optional | Optional | Yes | Yes | Yes | Yes | Yes |
| 1-bit mode | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
| 4-bit mode | No | No | Yes | No | Optional | Optional | Optional | Optional |
| 8-bit mode | No | No | Yes | No | No | No | No | No |
| Interrupts | No | No | No | No | Optional | No | No | No |
| Max clock rate | 20 MHz | 20 MHz | 52 MHz | 20 MHz? | 50 MHz | 208 MHz | 208 MHz | 208 MHz |
| Max transfer | 20 Mbit/s | 20 Mbit/s | 416 Mbit/s | 20 Mbit/s? | 200 Mbit/s | 832 Mbit/s | 832 Mbit/s | 832 Mbit/s |
| Max SPI transfer | 20 Mbit/s | 20 Mbit/s | 52 Mbit/s | 20 Mbit/s | 50 Mbit/s | 25 Mbit/s | 50 Mbit/s | 50 Mbit/s |
| DRM | No | No | No | Yes | Yes | Yes | Yes | |
| User encrypt | No | No | No | Yes | No | No | No | No |
| Simplified spec | Yes | Yes | No | Not yet? | Yes | Yes | No | No |
| Membership cost | JEDEC: US$4,400/yr, optional | SD Card Association: US$2,000/year, general; US$4,500/year, executive | ||||||
| Specification cost | Free | ? | Simplified spec: Free Full spec: Free to members, US$1,000/year to R&D non-members |
|||||
| Host license | No | No | No | No | Yes, US$1,000/year. No, if using SPI-mode only. | |||
| Card royalties | Yes | Yes | Yes | Yes | Yes, US$1,000/year | Yes | Yes | Yes |
| Open source compatible | Yes | Yes | Yes? | Yes? | Yes | Yes | Yes | Yes |
| Nominal operating voltage | 3.3 V | 1.8 V/3.3 V | 1.8 V/3.3 V | 1.8 V/3.3 V | 3.3 V | 3.3 V (SDSC), 1.8/3.3 V (SDHC), 1.8/3.3 V (SDXC) |
3.3 V (miniSD), 1.8/3.3 V (miniSDHC) |
3.3 V (SDSC), 1.8/3.3 V (microSDHC), 1.8/3.3 V (microSDXC) |
| Maximum available capacity | 128 GB | 2 GB | 128 GB? | 128 GB? | ? | 4 GB (SD), 32 GB (SDHC), 256 GB (SDXC) |
4 GB (miniSD), 16 GB (miniSDHC) |
4 GB (microSD), 32 GB (microSDHC), 128 GB (microSDXC) |
| Type | MMC | RS-MMC | MMC Plus | SecureMMC | SDIO | SD | miniSD | microSD |
- Table data compiled from MMC, SD, and SDIO specifications from SD Association and JEDEC web sites. Data for other card variations are interpolated.
Read more about this topic: Secure Digital
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