microSD is a format for removable flash memory cards. SD is an acronym for Secure Digital. It is commonly used in cellular phones, but also in handheld GPS devices, portable media players, digital audio players, expandable USB flash memory drives, and for Nintendo DSflashcards, along with 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. 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 microSDHCformat. 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 bySanDisk 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 4GB are only available as SDHC cards.
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.
Comparisons
| 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) | ||||||
| Specificationcost | 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 |
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