Memory Card Types

Memory cards for different devices come in many form factors and sizes, as different manufacturers tried to push there own technologies as well as supporting particular types, this led to a lot of confusion when purchasing memory cards whether it be for a digital cameras, mobile phones, tablets, MP3 player or other digital device. Fortunately the field has somewhat shortened as the popular types have lasted and some others have died out. This article will take you through the memory card types that are in production today or have been recently in case you have a device that still still uses an older type of memory card.

SD Card (Secure Digital)

By far the most popular type of memory card is the SD card (Secure Digital Card), this however does come in a variety of formats and sizes. The original SD cards were and still are full size cards and had a max capacity of 1GB, These were known as SDSC memory cards or Secure Digital Standard Capacity. The SDHC format did move on to allow for up to 4GB capacities but this involved a new driver version and would not be backwards compatible with host devices that were made with the first SDHC version 1.00, Version 1.01 started to allow capacities up to 4Gb by allowing the use of different block sizes in the memory cards file system.

SDHC

To allow for a greater capacity in the SD cards, the next generation was called SDHC or Secure Digital High Capacity cards. The SDHC format allows for a capacity of 32Gb to be achieved, for this to happen the FAT (file allocation table) had to changed to the FAT32 system and is not compatible with older SDSC host devices unless they are able to obtain the correct firmware updates from the manufacturer. Also older operating systems will require to be patched in order to recognise the increased capacities of these memory cards. Physically the cards are identical to each other and electronically the same also which is why only updated software is required.

SDXC

The SDXC stands for Secure Digital eXtended Capacity and have a theoretical capacity of 2TB. Host devices built around the SDXC format will accept all previous SD variants so its fully backwards compatible. SDXC cards are also physically identical to its previous incarnations, and also uses the same interface. Because of this SDHC host devices are able to accept SDXC cards however some SDHC host devices may face problems when using SDXC memory cards because of the file system. SDXC memory cards are preformatted with Microsoft's own exFAT file system, this is not like the others as its a licensed product and not supported by every SDHC device.

Classes of SD Memory cards

All SD memory cards are not made equal and their differences are shown in the form of a speed class system. While this is not particularly important when using an SD card in a digital camera to take single shots, it does matter when you are using them to record video and more so when recording HD video. The speed class will tell you how quickly the card can record data to the memory card in MB/s. The higher the video quality you wish to record the better class of SD card you will require.

Classes 2,4 and 6 show the cards sustained write speed on a memory card in a fragmented state while class 10 cards show a 10MB/s write speed but presume the situation is of a sequential write to a non fragmented card. This class system has superseded the previous "x" system which used a similar rating of speed to that of CD-ROM's where each multiple "x" was 150KB/s. To compare to two systems is not entirely accurate but as a rough guide they work out as below.

Physical sizes of SD Cards

As well as the standard size of SD cards smaller versions of the memory cards with the same technology were created to better suit smaller devices. MiniSD and MicroSD were technically the same as their larger brother but physically smaller and and could be used in order to fit mobile phones and mp3 players. Because they are of the same format electronically as the standard SD card, the smaller versions can be easily placed in standard SD card slots with the help of a physical adapter. Lots of MicroSD cards are sold with this cheap to produce adapter allowing it to be used in a large variety of devices. All the SD card types (SDSC, SDHC, SDXC) are available in all sizes except for the SDXC is not produced for the MiniSD size.

 xD Picture card

The xD Picture card format was developed by two major players in the digital camera market Olympus and Fujifilm. It was introduced into the market in July 2002 but has since lost a lot of ground over the more popular memory card types namely Secure Digital and Compact Flash. The main reason for this is that the others were able to branch out into other devices such as mobile phones, audio players and more. The xD picture cards are also slightly more expensive than their counterparts, the combination of these factors have led to the virtual downfall of the xD card and even Olympus and Fujifilm digital camera's started to support the rival memory cards either exclusively or alongside support for the xD Picture Card.

Type M / Type H cards

The original xD picture cards were limited to a maximum size of 512MB which was fine back in the day when the cameras were taking pictures in 1-2 megapixels, but now when we are looking at 16 megapixels that size is no where near enough. The Type M xD picture was released to to offer memory sizes with a theoretical limit of 8GB, however these cards suffered from lower read / write speeds than the original.

Type H cards were introduced to correct this problem and offered a theoretical 3 times faster read/ write speed than that of the original xD picture card. These cards were offered up to 2GB sizes in retail terms but could of been given higher capacities, however due to the production costs of these memory cards they were pulled from products in 2008.

The Type H card was replaced with a type M+ card that offered only 1.5 time the read / write speed of the original and again was only released in 1GB and 2 GB sizes

Compact flash memory was the most popular of the early flash memory cards. It was developed by SanDisk and is still widely used in many areas of the technology market. Compact Flash memory was designed with large capacities in mind and this has helped with the evolution of the format, while some products such as the SD card have had to alter the design to cope with sizes in multiple gigabytes such as the SDHC and SDXC formats, the Compact Flash cards based on the FAT32 system have simply been able to carry on increasing in size.

Differences between the Compact Flash media and others in the sector include the inclusion of the IDE / ATA protocol which allows this memory to act as a hard drive. They are thicker than most of the other portable media which allows them to take a little more wear and tear and are also easier to insert and remove from host devices. On the flip side of this they are not suitable for micro devices such as small mp3 players and smartphones, where as the the SD cards micro format is ideally suited for such devices.

Compact Flash is used in Microdrive's, these are tiny hard drives only about an inch long that are used in a variety of devices such as certain iPods and other media storage devices. While the Microdrive's are more susceptible to physical shock damage than memory card formats they do have a longer lifespan than flash memory.

Speed

The speed rating for compact flash are based on the IDE and CD-ROM calculations, where 1x = 150KB/s

Common speed ratings and the approximate read speeds :-

Memory Stick and Memory Stick Duo

The Memory stick format was developed by Sony in 1998. Like the other formats above it is used to store data on portable devices. The difference here is that the devices are usually of Sony's manufacture. Sony's Digital Cameras, music players, camcorders laptop ranges and mobile phones typically all have memory stick readers. The first memory stick released had a maximum capacity of 128MB, and such as all the formats above this became extinct very quickly as the need for greater capacity was required. The first response to was Memory Stick Select, This rather unpopular solution put two memory stick 128MB partitions together on one stick. In order to access the second partition however a physical switch was required and the user had to flip the switch to access each partition. This solution did not last long and work began on a more elegant solution to the capacity problem.

Memory Stick Pro

The Pro version of the Memory stick was a joint effort from Sony and SanDisk, it had a theoretical maximum capacity of 32GB although this version didn't see the heights of its capability. The bonus of this format is that it was physically compatible with the original memory stick. This allowed those devices that originally did not support the Pro format could be upgraded via firmware to support it. All Memory Stick Pro's that were over 1GB also support a high speed mode. The larger capacities of the Memory Stick Pro turned out to be more expensive than there counterparts and were not as popular as the SD card or compact flash formats.

Memory Stick (Pro) Duo

The Memory Stick Duo was created because of the growing need for smaller card sizes in order to fit the shrinking size of mobile devices such as phones and cameras. The Pro Version again replaced the original due to capacity sizes. The Duo provided all the same functions as the original but was 2/3 of the size. This format does also have a theoretical size limit of 32Gb but unlike the original Memory stick pro 32GB version were actually released and sold. Memory stick Duo cards can be used in slots that take the original memory sticks by a physical adapter. much the same as the SD cards adapter. this is because the cards are the same other than the physical dimensions.

Memory Stick XC

To increase the capacity of the Memory Stick even further the XC type was introduced, this used a new file system called exFAT. The limitations of the FAT32 system meant it had to be dropped along with compatibility with previous versions of the memory stick. This new format however allows for a theoretical maximum size of 2TB and a transfer speed of 60MB/s.