What You Need to Know About Flash Media (SD Cards)

NOTE: These are the show notes & resources presented in episode #4 of Your Technology Tutor. This program is available in the iTunes Store and can also be heard via the player at the bottom of this page.

Your Technology Tutor Program
Show Notes – Episode #4
Topic: What  You Need to Know About Flash Cards (SD Cards)

In this episode, Chet Davis presents info to help you better understand flash memory, especially SD card technology.

These are the little postage stamp sized cards that many of our digital cameras, digital video cameras and even Smart Phones use.

There are a number of card formats like Memory Stick Duo, some Compact Flash units still in use but the great majority of consumer electronics devices that require the use of these removable memory cards use the SD family.

First a note – when I say memory, these little cards are used by our devices to save or store data onto them.  Digital photos, video and in the case of mobile phones & tablets/pads – these can be used to also store audio,documents and apps (software).

This technology is called Flash Memory because unlike the traditional computer hard drive or disk drive there is no moving part, no spinning platter that the data is recorded onto.. instead the data is recorded or written onto an array of memory cells made of transistors, developed by a scientist working for Toshiba in 1980.  According to Toshiba, one of the inventors colleagues suggested the name Flash as the erasure process reminded him of the flash of a camera
Flash memory offers fast read access times and Its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, being able to withstand high pressure, temperature, etc

We’ll look at understanding the different types of Flash Media by reviewing their 3 categories that differentiate them: Format, Capacity, and Transfer Speed.  Well also take a quick check in with a specialized SD card… one that has built-in WiFi capability and we’ll talk about the best way to store the cards, and what to do if you experience a malfunction of a flash card.


Card FormatSD Flash Cards

In the SD (Secure Digital) Card family – there are three different sizes (formats) of cards, SD, miniSD, and microSD. These three formats are pictured at left – nested on top of each other to clearly show their size. 

I should mention that the miniSD card is becoming less used while the other two formats continue their implementation in different devices – the smaller format (microSD is largely used in smaller devices like Smart Phones.


Card Transfer Speed
Speed Class and UHS Speed Class
Speed Class is the means of measuring & identifying the minimum performance  of the device to ensure quality recording (and playback of video, photos, and other data).  People can and do experience different rates of recording speed depending on the device they are using but these Class ratings should be the minimum you would expect to obtain.

The traditional measurement or standard is the Speed Class which is a rating attributed to all 3 formats, SD, SD mini and SD Micro.  
the newer, higher speed technology called UHS (Ultra High Speed) is only found on some, and the latest SD and SD Micro cards.

I should point out that these ratings are determined by each manufacturer for their device even though the standards are set by the industry group known as the SD Association.

The Class ratings of SD cards are posted with the letter C (almost looks like an unfinished circle) with a numeral inside the C, like this 28px-SDHC_Speed_Class_4.svg

When review the chart below – the minimum performance column represents the measurement of DTS or Data Transfer Speed.

SD Card Speed Class Rating

This is one of the most critical decisions to make when purchasing cards for your cameras and video camcorders.  This is not where you want so save a few dimes by going with a lower speed card.

UHS_1IF and that’s a big IF… you have a device that is compatible with the newer UHS SD card format, you should consider using the SD or SD Micro card labeled as UHS-1… the icon is a letter U with the numeral 1 inside of it (shown at right)

This newer  technology is available on some SDHC and SDXC cards and gives a transfer speed  up to 50MB/second.  There is even the option when using what is called a higher clock frequency inside the device that it could reach speeds double that — at 104 MB/Second.

And for the future there is a technology designate at UHS-2 (roman numeral 2) that raise the theoretical data transfer speed to 312 MB/Second (that’s 30times faster than today’s Class 10. But there are no components or devices available commercially that match this capacity yet… of course as this program stays around in the archives this will be the speed of choice

Card Capacity
Now that you have a better idea which Speed Transfer Speed to select, let’s talk about Capacity.  This is the amount of data that can possibly be stored on a Flash Card.

Here is a chart providing an estimated capacity for different card sizes:

SD Card Capcity chart

When selecting cards remember:

  • A newer card may offer greater capacity than the host device can handle.
  • A newer card may use a file system the host device cannot navigate.


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Here are some tips to using SD Cards successfully…

• Keep the cards in their case when not in the device.  Many times the Card comes with its own plastic case. Use it – this will prevent the metal contacts from being affected by other particle or possible an electrical discharge or issue coming into contact with another electronic device.  And it keeps the card more safe from damage, junk, liquid, etc.

• Put your cards int a safe spot in your desk, or in your camera bag. I have a little zippered case I use when i travel to keep my cards in and organized.

• Don’t leave your cards in environments that will expose them to temperature extremes, moisture, other chemicals.  Avoid bending them or exposing them to magnetic currents.

• Don’t turn off your  camera too quickly after capturing a photo or recording video — let the recording process complete full (just because you’re done does not mean your cameras is)

• Switch your camera power off before removing/inserting a card.

• Format a new card with the camera you’ll e using it in. If you switch you’ll notice sometimes the camera will reject or not detect a use-able card.  The formatting process is different for each cameras – check your owners manual… and use care not to format a card that has data you want to keep — reformatting involves erasing what’s on there already!

• Some photographers recommend not filling up your card to top capacity – they find it can lead to card irregularities and problems.

• Keep your camera battery power from dropping too low – it could affect memory card performance (still work but not well)

• ALWAYS take more than one card with you, if one card fills up or malfunctions you have at east one more card to capture those precious moments. (and it is usually much more affordable to purchase cards ahead of time then when on vacation overseas, at a resort, or in the middle of nowhere).

• Some folks advise deleting image/files only while connected to a computer – and not to delete while the card is in your camera. The thought being that the process is more easy to control on your big screen and avoids accidental erasure of the scene/photo you wanted to keep.  Also, deleting a bunch of image in your computer results in only one erase cycle for the card rather than multiple cycles in your cameras in the field.

• When done with a card in your computer -make sure you remove or eject the card prior to removing it.

• Label your cards – with a little numeral to keep track of which card you used last.

• Take a photo of your business card or luggage tag and save it onto the card… if it is lost, it is more likely to be found and returned to you.

And if you accidentally erased data on one of your cards there is the possibility you may be able to regain or access them.  You may know when we delete data on a computer or device, it removes the file from access but is often not gone until we re-record or write over that file or data.  Here is one software application for your computer that some folks use to retrieve data from their erased SD cards: www.cardrecovery.com

For additional information about the SD Card Family – see the SD Card Association website