Micro SD and SDHC Cards

SD cards were formally known as T-Flash and later Trans-Flash and produced by SanDisk. The year 2000 saw the SDA (secure digital association) formed by three major companies Matsushita, Toshiba and SanDisk. The association then took over the development of the new memory card to be called the SD cards.

The micro SD is the smallest memory card in today market, its size 15mm-11mm-1mm and are used in mobile phones, digital cameras, hand held computers and gps devices and many more.

SDHC(secure digital high capacity)

The SDA developed a new card called the SDHC and it was built to 2. 00 specifications. The standard micro card is the same dimensions but unless the host device recognizes the new specification it will not work. Both the micro SD and the micro SDHC are compatible with an adapter in devices using standard SD cards and usually comes with a electro mechanical adapter for use in those devices.


The micro SD/SDHC Cards are available with the following storage capacity:

micro SD: 32/MB, 64/MB, 128/MB, 2/GBs

micro SDHC: 4/GBs, 8/GBs, 16/GBs, 32/GBs


DTR stands for data transfer rate.

microSD (DTR)

The rate in which the memory card will except information to be stored, or in which the rate is reads from the card. The standard micro SD has a data transfer rate of 100 Mbit/s and a maximum SPI rate of 25 Mbit/s which os optional, it has 8 electrical contact pins on the underside the same as the micro SDHC.

microSDHC (DTR)

The SDHC comes in four memory sizes as we now know but each card comes with five speeds DTR rates they are class 2, class 4, class 6, class 8, class 10. These are the transfer rates either 2MB, 4MB, 6MB 8MB or 10MB per second. That is a minimum transfer rate, what if we want to know the maximum rate how do we find that answer. Well you will need a card reader (not expensive) and do your own test.

Here is an example, using an internet card reader(goes in the floppy dive)

SDHC 6 GB CLASS 6 memory card

minimum DTR 6MByte/s

after test:

write rate 7. 34 MByte/s – read rate 14. 1MByte/s

so you see there are two rates and this is really important when using a advanced camera taking video or multi pictures to be able to transfer without a hiccup. Some manufactures put their rate on the cards but not all.

FILE systems of the standard micro uses FAT 12 or FAT 16 the newer SDHC uses FAT 32 which gives the card higher capacity storage of 4 GB TO 32 GB and of course it complies with the new specifications.

The approved logo must be on the memory card to make sure it applies with the new regulations, if its not on then it may not have the new specifications of 2. 00

Todays mobile phone market SD has a largest share, in 2009 they had 76% of all memory card sales and has taken over from the TOSHIBA Smart Media. The SD cards in all ranges are covered by patents. US patent 5602987


SD standard,

microSD standard

miniSD standard

SDHC standard

microSDHC standard






Source by Clive Murray