Taken from the Learn Photography Master Thread. All about memory cards
While buying a memory card appears at first glance to be an ultra-simple affair, there are actually many factors to consider. Your choice of card can make a tremendous difference in your day to day shooting. Let's have a look at the numbers, standards, and features you should be aware of when buying a card for your camera. Types of card
There are a few different types of memory cards on the market today. Generally the type you need will be dictated by your camera; if it takes an SD card only there's no way you could use a CF card in it. There are however a number of cameras that accept more than one type. Since the most common card by far is SD, I'll focus mostly on that. Compact Flash (CF):
These are the bigger, square memory cards. These days they're mostly used in pro cameras such as the Canon 5DMkII or the Nikon D800. The advantage of CF over SD is mainly in physical strength. While SD cards are prone to braking, a CF card is virtually indestructible. On top of that, they tend to be a bit faster than SD cards, meaning that any new jump in performance will appear in the CF market before the SD market. The one disadvantage with CF cards is that the socket relies on a series of pins, which are easily bendable. Secure Digital (SD):
This is the most common card type in use by far. If you have a camera, chances are it takes SD cards. These are smaller than CD cards (about stamp-sized), and are not as strong physically. I have an entire collection of cracked and broken SD cards flying around the house. The 'secure' part of the name refers to the read/write protection switch on the side. To be honest this feature is mostly useless, and only adds to the complexity, and therefore breakability, of the card.
SD cards come in a couple different flavors:
This mostly obsolete standard was for cards under 2GB. They could still be bought today, but why someone would is anyone's guess.
- SDHC (High Capacity):
This is the most commonly used standard today, and covers cards from 2 - 32GB. Virtually every camera in existence supports the SDHC protocol.
- SDXC (Extreme Capacity):
This is the newest SD standard and supports cards from 64GB all the way up to a theoretical 2TB. This uses the exFAT file system, and so will not work on some older computers. Most newer cameras will support SDXC.
This is a tiny version of a regular SD card, and also comes in all three SD flavors. Due to its size it'll be more expensive than a comparable full-size SD card, as well as being very prone to getting lost. It is used in most smartphones, as well as some point & shoot cameras and video cameras (the GoPro for instance).
- SD cards also come in a veriety of wireless models. These cards will automatically upload pictures to your computer via Wi-Fi. Memory Stick (MS):
This is a proprietary Sony card, and is used only in their cameras. At one point this was a horrible mess with as many as 10 types of Memory Stick on the market, none of which was compatible with the other. These days Sony has cleaned this up, with only the Memory Stick Duo surviving. More importantly, Sony finally buckled and now all their cameras accept SD cards as well, so you could easily forget about this overpriced card and move on with your life
There is also the new XQD card
, which so far is used only by the Nikon D4 camera. Card Speed:
This is the most important thing to know when choosing a memory card. Today's cameras move a massive amount of information to the card every time you take a picture or video. If your card is not fast enough, you will have to wait for a couple of seconds after every picture, as well as when looking through your pictures on your camera. Video-wise, if the card isn't fast enough the camera will drop frames, which will cause your video to be choppy and jittery.
Unfortunately, card manufacturers try their best to confuse the bejiggers out of you with an overwhelming amount of different speed specifications. Let's have a look at all these specs, and what they actually mean.
The first thing to remember is that pictures and video require a completely different type of speed in order to work properly. With pictures, you're throwing a huge amount of data at the card in short, intense bursts. On the other hand, the video data stream is much smaller, but continuous. With that in mind, let's have a look at the specs. Rated Speed - written as MB/s:
This is the maximum
speed of writing chunks of data to the card, and applies to photos only
. Common speeds you'll find are 45MB/s or 60MB/s. This means that the theoretical transfer speed will be 60 megabytes per second. Why is this important? Take a Nikon D600. Each RAW file is about 28MB. That means that if I use a card rated at 30MB/s, I will have to wait a second between each picture. Now imaging I'm shooting continuous - if I take 8 pictures in about 2 seconds, I then have to wait 6 more seconds until the camera is ready to shoot again, since it has to finish writing all this data to the card. This means that I will keep on waiting, and keep on missing shots.
Now imagine I had bought a faster card - say 90MB/s. This means that I would never have to wait between pictures (since each picture will take about a third of a second to write). Shooting 8 pictures in 2 seconds, I would have to wait less than a second until I'm ready to shoot again.
If you have any newer high-megapixel camera, this should be the number one spec you look for. It will be the difference between taking pictures and forgetting that a memory card exists, and between getting stuck waiting all the time and cursing the card out for making you miss the shot yet again. X Rating:
This will be written as 400x, 533x, etc. This means the exact came thing as Rated Speed, and is a direct conversion. It is simply another way for the card companies to drive you nuts. Each 'x' is equivalent to 15KB/s. Doing the math, 400x will be 400*15=6000, which would be 60MB/s. Class Rating:
This will be written as Class 6, Class 8, Class 10, etc. This applies to video only
. What this is the minimum sustained write speed. A class 10 for instance, will maintain a write speed of at least 10 megabytes per second. Currently, no standard camera exists which can take advantage of anything over Class 10. This means that if you have a Class 10 card, your card will always be fast enough to keep up with the video data stream being thrown at it. UHS Class:
Again, this is a direct conversion from Class Ratings. UHS-1 simply means 10MB/s minimum sustained speed, which we already know is Class 10.
So basically you have to look at only two specs: Rated Speed and Class Speed. The Rated Speed will tell you how large a chunk of data (photos) you could transfer at one time, while the Class Rating will tell you the minimum continuous (video) data speed. Read speed vs. write speed:
Another very important thing to remember is that the Rated Speed applies both to read and write speed. That means you have to be very careful reading the specs, as some brands (ahem Lexar ahem) have wildly different read and write speeds, and write only the higher number in big obvious text. For example, their 60MB/s Class 10 SD card is actually only 20MB/s
write, while the 60MB/s is only on read. This means that it's still quite slow in your camera; only transfers to your computer will be fairly fast. This is of course extremely misleading, so keep your eyes peeled. Memory Brands
Does it matter which brand memory card you got? Heck yes. Memory is cheap enough these days that you could afford to buy the best; saving $10 to go with a lesser brand in absolutely not worth it. Behold: Chip Quality:
At the very basic level of a memory card sits the humble silicon chip. These chips start their life as a large, circular wafer around 18" in diameter. This wafer is subsequently cut into a couple dozen square or rectangular memory modules. Due to the manufacturing processes, the closer to the center of the wafer the module comes from, the more perfect and free of defects it will be. Since flash memory is a commodity market, there are two or three companies which control most of it. These companies will take the highest quality center modules for themselves (or their partners), and let the little fish scramble for the inferior, cheaper ones.
What all this means for you is simple: The higher priced memory cards are priced like that for a reason: they use the highest quality chips. End of story. Sandisk and Lexar are on the top, followed very closely by Sony and Panasonic. Kingston is somewhere in the middle, and companies like Transcend are just about on the bottom of the food chain. The only thing lower are all the no-name brands - Dane-Elec, Wintec, Silicone Power, et. al.
Why do you need a high quality chip? Because a cheap one will
eat your pictures one day. They are prone to getting corrupted and can't be erased and reused too often before they start to deteriorate. Would you trust your pictures to the lowest common denominator to save a few bucks? Personally, I don't think it's worth it. Now mind you - I've had Sandisk cards conk out on me; nothing's foolproof. But after years of hearing first-hand horror stories from countless people, the simple fact is obvious: It's not worth it to cheap out on memory. Claimed Specs:
Very often, you'll find with the cheaper brands that their claimed specs are often inaccurate and are actually slower then claimed. Physical Quality:
Look at any Sandisk box above the Ultra level (which is just about all of them): waterproof, temperature proof, and shock proof. I've put Sandisk cards through the wash and they work as good as ever. You won't find that with cheaper brands. Drop a card and chances are it'll break; leave it in the sun too long and it may not work again. The higher quality brand, the more the card will survive. Imaging coming home from vacation and finding that your full memory card cannot be read. With cheap cards, this is a far more common occurrence than with good ones.
Note that SD card are an inherently weak design and every one of them will eventually break. The difference here is how long it take until that actually happens, and if the data could still be read off it at that point. From my entire collection of broken Sandisk cards, all but one still technically work - that is, I could still read and write to them properly. Not that I'd want too; but the point is that I didn't actually lose any data when it broke.
__________ Lesson Summary: Card types:
- CF cards are mainly used in pro cameras these days
- SD cards are the most common:
--- SD is up to 2GB
--- SDHC is 2 - 32GB
--- SDXC is 32GB - 2TB
- MS is a Sony proprietary and could safely be ignored these days. Specs:
- Rated Speed gives you the maximum read/write speed in MB/s. Used for pictures only.
- X Rating gives you the exact same thing as 300x, 400x, etc. Multiply by 15 to get the MB/s.
- Class Rating gives you the minimum sustained data stream as 1 per class. Class 8 is 8MB/s, Class 10 is 10MB/s, etc. Used for video only.
- UHS Rating gives you the exact same thing as Class. UHS-1 is the same as Class 10.
- Be vigilant and check both the read and write speeds. They may be very different from each other. Brands:
- Cheaper brands use cheaper, lower quality chips.
- Lower quality chips are very prone to failure.
- Cheap brands often fudge their numbers so their cards appear faster.
- Cheaper cards are often physically weaker and may break earlier.