Secure Digital - Comparison To Other Flash Memory Formats

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.


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