Memory cards: Compact Flash and SD (2012)

The Compact Flash (CF) and the Secure Digital (SDHC/SDXC) are the standard in almost all SLR cameras. Nowadays, both CF and SD have reached high capacity and great speed; they are a solid state memory (they don't have moving parts), so they are very reliable and resistant to humidity, high or low temperatures, droppings.

 

The SanDisk Extreme Pro 64 GB, one of the finest CF cards on the market.
 

The evolution of memory cards

In the early years of digital photography (2000-2002), there were many memory card formats, and cards capacity was measured in MB, with speeds of few hundreds of kb per second. With time, many format have disappeared, and nowadays CF and SD are the standards. The evolution has brought lower prices, much bigger capacities and higher speeds, and nowadays the memory cards have reached 128 GB of size and speed of 100 MB/s.  
 
Compact Flash are bigger than SD and for years they have remained physically unchanged; in 2009 it has been announced a new standard, the CFast, that is an evolution of CF: CFast is based on the Serial ATA bus, rather than the Parallel ATA/IDE bus of Compact Flash, and it allows to reach a max speed of 300 MB/s (the theoretical maximum for CF is 133 MB/s). Nowadays there are not yet CFast cards on the market, nor CFast compatible cameras.  
 
Secure Digital cards have had two great evolutions; in 2006 they have evolved in SDHC (that are currently the standard and reach a capacity of 32 GB), and in 2009 the SDXC format has been announced. SDXC has a theoretical max capacity of 2 TB and speed of 300 MB/s; the first cameras compatible with SDXC has been announced by Canon and other manufacturers in January 2010. Toshiba and Panasonic have recently announced their first SDXC cars with a capacity of 64 GB and speed of 35 MB/s (233x); the price for these cards is pretty high ($600), but I expect to see lower prices as soon as the SDXC will become more mainstream.
 
 

Size and speed

When you chose a memory card, there are two things to evaluate: size and speed. Usually you can not choose between SD and CF, because the majority of cameras support only one of these formats, so you have to use the format supported by your camera. If you have one of the few cameras that support both (e.g. Canon 1D Mark IV, Nikon D300s), I recommend the CF if you want speed, while the SD may be a good choice if you have other cameras that support only this format, or if you want a card that can be read directly by your computer, without using an external card reader (the majority of laptops and some desktops have a SD card reader).  
 
Size depends by the camera you use and by your current needs. As generic guideline, for a trip with plenty of photo opportunities (for example a Safari) I estimate a maximum of 5-7 GB per day with a 10-12 megapixel camera, or 10-15 GB per day with a 20-25 mp camera. In other kinds of trip (trips for landscapes or macro) I use much less storage because I don't use the continues shooting and I am more selective.  
 
Some photographers prefer to buy many low-capacity cards instead of a single high-capacity card, because they fear to lose all their photos if the card fail. This is a controversial topic; in my opinion, having a lot of card just increases the risk to lose one of them. The CF and SD are very reliable, and it is very unlikely that they fails. It is curious to see that many are so worried about CF/SD cards, then they store all their photos on the single hard disk of the computer, a much less reliable support, without even thinking about back-up copies in the (likely) possibility that the computer hard disk fails, due to software problems, virus or other factors. Anyway; this is just my opinion, I prefer to use a couple of large card, but of course everyone is free to use the card size he prefers! :-)  
 
Speed depends by the kind of photography you do and by the use of video. If you do wildlife photography and you use a lot the continuous shooting, a fast card is a plus because it allows to empty the buffer in few seconds. For landscapes and macro, a fast cards is a waste of money. If you take HD videos, you need a card with a good write speed to avoid dropped frames; in this case I recommend a card that has at least a write speed of 200x (30 MB/s). A very important thing to remember is that the actual speed varies widely depending by the camera - if a camera has poor write speeds, you can use even the fastest card of the world, but you will get slow write speeds.
 
 

Frequently Asked Questions about CF and SD

What does manufacturers speed ratings mean? every manufacturer give a "x" rating to the card. For CF and SD cards, an "x" means 0.15 MB/s, so for example a card that is rated 133x should be able to write at 20 MB/s (0.15 x 133). That said, the actual speed is often lower than the rated speed, it depends by the camera you use.  
 
How do I know the actual speed of the camera? You can ask on JuzaForum to receiver owners' opinions; other than that, I recommend to check the Rob Galbraith CF/SD database (it is not updated very often but overall it is a good resource).  
 
What brands do you recommend? SanDisk and Transcend are my favorites; other good brands are Lexar, Panasonic, Kingston. I'd suggest to avoid unknown brands as they may be less reliable than the mainstream brands.  
 
What speed do you really need? You don't need the fasted card on the market! If you take "action" photos, for example birds and wildlife, and you use a lot the continuous shooting, a fast card is a big help to be always ready to shoot. But if you take mainly landscape or macro photos even a slow card is ok! Currently, I use Transcend 32 GB 133x cards for my 1DsIII: there are much faster cards, but the Transcend 133x are enough for my necessities, and they are much cheaper than faster cards.  
 
How much storage space? I recommend to choose the card size according to your current necessities...don't think about what you may need after six months or one year, think about what you need now. The prices of memory cards drops quickly, so cards are not a good investment - what you buy now for $100 after one year or less will be available for $50.  
 
Which cards do you use? I have three Transcend 133x 32 GB CF ($100). They are not super fast but they are cheap and they offer huge capacity; that said, nowadays for few more dollars you can get the much faster Transcend 400x 32 GB CF ($180). In future I'll replace them with two Transcend 64GB 400x ($400), but I don't have immediate necessity so I'll wait some time until the price of these 64 GB cards come down :-)  
 
What is the largest card currently available? Both Pretec and Silicon Power have a 128 GB CF card, but between the mainstream cards - those you can find in every shop - the largest ones are currently the SanDisk 64 GB Extreme Pro 600x ($ 700) and the Transcend 64 GB 400x ($ 400).  
 
What is the fastest card currently available? The SanDisk 64 GB Extreme Pro 600x (90 MB/s) is currently the fastest card on the market; it costs $700. (the Pretec 667x may be a bit faster, but they are very rare)  
 
What about portable HDD (e.g. Epson P5000)? I consider them a thing of the past. Nowadays with few high capacity CFs you can cover an entire trip; memory cards are more reliable and they do not require energy. During my trip to Tanzania in 2008, I met a couple of photographers who has four portable HDDs...after ten days, two of these HDD had failed, due to the dusty environment and to the frequent bumps you get in the jeep. In years of photography, instead, I have never had a problem with a flash memory.