SD Memory Cards

SD memory cards are things we seem to take for granted

I recently saw an item on the BBC technology news pages announcing the launch of a 512gb SD card. These tiny devices, measuring just 32 X 24 X 2.1 millimetres are now the standard storage method for digital cameras – both still and video. Indeed, the same news item mentions that the motivator for developing such a large capacity SD card is the latest “4X” standard for video production. This can require up to 5gb for every minute of video shot.

The price of this new Sandisk card is £490. At first glance this may look expensive, but it’s less than £1 per gigabyte and the price is bound to drop as sales rise. Note that this entire article looks at SD cards – not solid state hard drives (very different animals).

From my own experience of computer support clients who use SD cards at all, it seems most people just accept that they are the storage method in their cameras and don’t use them for anything else. Moreover, if they transfer their images to a computer via a cable (instead of by removing the SD card and sticking it in their computer) then they probably never give the card a moment’s thought.

SD cards do have other uses, though.

Imagine, for instance, that you use a laptop or notebook computer that you carry around with you but work at home or in the office on a “proper computer” (ie a desktop computer). There are often going to be times when data needs to be transferred from one machine to another. Not all people want to solve this problem by storing stuff “in the cloud”, available to any device that connects to it. Instead, they will usually resort to the more common method of transferring data via a USB flash drive (also known as a thumb drive, USB stick etc). The problem with these is that they stick out of the machine. You wouldn’t be at all wise to pack your laptop into your case with 2 inches of USB drive sticking out of it. Why not use an SD card instead? Most computers (especially laptops) have a slot specifically for SD cards. Just push the card into the slot and the machine recognises the SD card just the same as an external hard drive or a USB flash drive. The card will either be flush to the machine’s case or, at worst, stick out a couple of millimetres.

Since the card doesn’t obtrude, you can leave it there forever if you want and use it as a backup drive. Used this way, it could save you from disaster in the case of hard drive failure but, it must be admitted, it won’t be any good as a backup if you leave your laptop in a taxi. Oops.

SD cards do come even smaller – physically – than the standard size. A “micro” version of them is very often used for storage on smartphones (except iPhones. IPhones don’t have any expandable storage). These micro SD cards can also be placed in an adaptor that makes them readable and useable as a standard SD card. Micro SD cards measure just 15mm X 11mm X 1mm. I’ve got a32gb micro SD card in my smartphone that has 7435 files on it. These are almost all music tracks, so that’s about 750 albums on a device smaller than a fingernail. Things have come a long way since the original Walkman, when carrying around more than half a dozen music cassettes seemed a bit obsessive!

The instructions for my smartphone (a Sony Xperia) specifically say that it can use cards up to 32gb. This probably means that it is limited to the “SDHC” version (which means Secure Digital High Capacity). If it were compatible with the latest standard (SDXC) then it could use the new Sandisk card mentioned above and any bigger cards as they are released – right up to 2tb (this is 2 terabytes, also expressed as 2000gb).

Apart from storage capacity, another factor to bear in mind when buying SD cards is the speed at which they can read and write data. Obviously, faster cards are more expensive. The speed is expressed in a “class” number. Most cards indicate that they are between Class 2 and Class 10 (where the figure represents the number of megabytes per second that can be read or written. The card must be able both to read and write at the stated speed). Even faster cards are UHS 1 and UHS 3 (representing 10mb and 30mb per second respectively). Class number doesn’t matter so much if you’re using the card for still images, but go for a high class number if recording video or if you take still images in “bursts”.

The music for my smartphone is on a UHS1 card and it performs faultlessly. The last one of these I bought cost about £25. Not bad for storing about 750 albums. That’s about 3.3p each. Compare that with the old “CD90” cassettes that cost about £1 to record two 40 minute albums. And just imagine the pockets you would need to carry 375 cassettes, each with 2 X 40 minute albums on!

Click this link for an even nerdier look at the humble but hard-working SD card.