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Health & Fitness

SD or CF – which memory card?

Edgar W. Reece's profile picture
Edgar W. Reece, Neighbor

Chances are high that you have a portable device that requires a memory card. It could be a camera or even a phone with a memory card slot. While these cards are useful, they do present one problem: There's so many different types and subtypes that it can be taxing to distinguish the difference between them and figure out which is the one you need.

This article is an overview of the two most popular types of removable memory cards that most electronics use: SD and CF.

SD Secure Digital cards, more commonly known as SD cards, are the most popular storage medium for smaller devices like smartphones and most digital cameras. There are three main types of SD card:

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  1. SD
  2. SD Mini
  3. SD Micro
Regular SD cards are the biggest, at 32mm length and 24mm wide. SD Micro cards are the smallest at 11 mm length and 15mm wide. If you have a device that can support SD cards, it's important to know what size of card you need. You can usually find this out in the tech specs of the device.

Each size of SD card usually comes in three different types. This designation actually dictates the maximum storage capacity of the card:

  1. SDSC - SD Standard Capacity - can store up to 2GB of data. Some cards can go as high as 4GB.
  2. SDHC - SD High Capacity - can store up to 32GB of data.
  3. SDXC - SD eXtended Capacity - can store up to 2TB (Terabytes) of data, although the highest you will likely see at this time is 128GB.
You can usually tell what type of SD card and the storage capacity by looking at the packaging it comes in. Some cards even have the size printed on the card itself. The key issue to be aware of here is that devices can only support a limited amount of memory. For example, older phones can only support cards up to 32GB. If you buy a card with a 128GB it may not work, or you will only be able to use 32GB of space, depending on the device. So, when buying a card it is recommended that you know what type of card is supported. This can usually be found in the device's tech specifications.

Another important point to be aware of with SD cards is the write speed - how fast data can be written, or saved, on the card. Manufacturers designate their SD cards in classes. Most manufacturers will use one of five class designations:

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  1. Class 2 - These cards write at 2MB per second.
  2. Class 4 - These cards write at 4MB per second.
  3. Class 6 - These cards write at 6MB per second.
  4. Class 10 - These cards write at 10MB per second.
  5. UHS (Ultra High Speed) Class 1 - These cards write at 10MB per second and faster.
As a rule of thumb: The higher the class, the faster the read speed and the faster images or data can be saved. Most modern devices require at least a class 6 card, especially if you plan on capturing high definition images and video.

CF CF, or Compact Flash cards, are traditionally found in higher-end cameras like DSLRs. These cards tend to be much larger than SD cards, measuring 36mm length by 43mm wide. They are generally more robust - able to work harsher conditions - than their smaller SD counterparts.

Currently, CF cards are available with up to 128GB of storage capacity. While this is seemingly lower than SD cards, CF can write data a heck of a lot quicker. Take a look at most CF cards, and you will see the words UDMA - Ultra Direct Memory Access. This technology allows for faster data transfer between the memory card and the device.

There are eight different UDMA numbers which indicate how fast data can be written.

  1. UDMA - can write at speeds up to 16.7MB per second.
  2. UDMA 1 - can write at speeds up to 25MB per second.
  3. UDMA 2 - can write at speeds up to 33.3MB per second.
  4. UDMA 3 - can write at speeds up to 44.4MB per second.
  5. UDMA 4 - can write at speeds up to 66.7MB per second.
  6. UDMA 5 - can write at speeds up to 100MB per second.
  7. UDMA 6 - can write at speeds up to 133MB per second.
  8. UDMA 7 - can write at speeds up to 167MB per second.
Currently, most Compact Flash cards are UDMA 7. To figure out how fast the write speed is when looking at a card look at the packaging. It should say UDMA on it, and have the write speed beside it, or on the back.

If you are looking for a new memory card, it's important to pay attention to what your device's manufacturer recommends, largely because these cards - both SD and CF - can be expensive.

Looking to learn more about memory? Why not give why not contact ISN Global Enterprises (www.isnglobal.com) today, they'd be happy to sit down with you.

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