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microSD

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A generic 8 GB class 6 (6MB/s) MicroSD HC card. Shown on a US dime coin for reference.
An SD card, miniSD card, and microSD card.
2 GB MicroSD

microSD is a format for removable flash memory cards. SD is an acronym for Secure Digital. The cards are commonly used in cellular phones, as well as in handheld GPS devices, portable media players, digital audio players, expandable USB flash memory drives, Nintendo DS flashcards, and digital cameras.

It is the smallest memory card available commercially; at 15 mm × 11 mm × 1 mm (about the size of a fingernail), it is about a quarter the size of an SD card.[1] There are adapters which allow a microSD card to be used in devices intended for SD, miniSD, Memory Stick Duo and even USB cards. However, they are not universally compatible. Many microSD cards sold online and in stores are packaged with an SD adapter to use the card in devices that take SD cards. TransFlash and microSD cards are the same (each can be used in devices made for the other), except that microSD adds support for SDIO mode, enabling non-memory cards like Bluetooth, GPS, and Near Field Communication devices.[2]

A point of confusion can come from the difference in the microSD and the newer microSDHC format. The SD and SDHC share a similar form factor, but not all devices are compatible with the newer high capacity format. This is even true with devices that have been developed by SanDisk such as their e200 series of MP3 players. Using 3rd party firmware however, SDHC reading capabilities can be possible.[3]

As of September 2008, microSD cards are available in capacities from 64 MB to 16 GB.[4] A 12 GB version was developed by SanDisk but never released.[5] Cards with sizes over 2GB are almost all SDHC cards, though some early 4Gb SD Cards are not SDHC.

Contents

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[edit] History

The microSD format was originally created by SanDisk. It was originally called T-Flash, and then TransFlash, before being renamed microSD when adopted by the SD Card Association (SDA). Other flash card formats approved by the SDA include miniSD and SD card.

The SDA announced the microSD format at CTIA Wireless 2005 on March 14, 2005, and approval of the final microSD specification was announced on July 13, 2005. At launch, the microSD format was available in capacities of 32, 64, and 128 MB. SanDisk introduced a 2 GB microSD card in July of 2006, initially priced at 99 USD. Since then, prices for flash memory devices have fallen dramatically. The same 2 GB card as of April 2009 can be found for as little as 12 USD at department stores, and as of May 2009 for as little as 6 USD at online electronics stores.

Today 16GB versions are on the market for under 50 USD.

[edit] Comparisons

Comparison of technical features of MMC and SD card variants
Type MMC RS-MMC MMC Plus SecureMMC SD SDIO miniSD microSD
SD Socket Yes Mechanical adapter Yes Yes Yes Yes Electro-mechanical adapter Electro-mechanical adapter
Pins 7 7 13 7 9 9 11 8
Form factor Thin Thin/short Thin Thin Thick (exceptions possible) Thick Narrow/short/thin Narrow/short/extra thin
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 (exceptions possible) 2.1 mm 1.4 mm 1 mm
SPI mode Optional Optional Optional Yes Yes Yes Yes Optional
1 bit mode Yes Yes Yes Yes Yes Yes Yes Yes
4 bit mode No No Yes  ? Optional Optional Optional Optional
8 bit mode No No Yes  ? No No No No
interrupts No No No No No Optional No No
Xfer clock 0–20 MHz 0–20 MHz 0–52 MHz 0–20 MHz? 0–25 MHz - 0–50 MHz 0–25 MHz 0–25 MHz? 0–25 MHz?
Max Transfer 20 Mbit/s 20 Mbit/s 416 Mbit/s 20 Mbit/s? 100 Mbit/s - 200 Mbit/s 100 Mbit/s 100 Mbit/s 100 Mbit/s
Max SPI Transfer 20 Mbit/s 20 Mbit/s 52 Mbit/s 20 Mbit/s 25 Mbit/s 25 Mbit/s 25 Mbit/s 25 Mbit/s
DRM No No No Yes Yes N/A 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 $2500/yr (not required) $2000/yr (General), $4500/yr (Executive)
Specification cost free since version 4.3  ?  ? Member Member Member Member
Host license No No No No $1000/yr + membership cost
Memory card royalties Yes Yes Yes Yes Yes Yes Yes Yes
I/O card royalties N/A N/A N/A N/A N/A Yes: $1000/yr + membership cost N/A N/A
Open source compatible Yes Yes Yes? Yes? Yes Yes Yes Yes
Nominal Operating Voltage 3.3V 1.8V/3.3V 1.8V/3.3V[6] [7] 1.8V/3.3V 3.3V [8]
Type MMC RS-MMC MMC Plus SecureMMC SD SDIO miniSD microSD

Table data compiled mostly from simplified versions of MMC and SDIO specifications and other data on SD card and MMC association web sites. Data for other card variations is interpolated.

Capacity limit in all SD/MMC formats appears to be 128 GB in LBA mode (28-bit sector address).

[edit] See also

[edit] References

[edit] External links