What the SDHC "Class #" means... be aware!

**Marc Langille** · 02-01-2008, 08:14 PM

For the newcomers:

The Class # refers to the card's throughput in MB/sec. A Class 6 SDHC card is the equivalent of a 40x write speed (6 MB/sec.). The majority of SDHC cards are NOT any faster than Class 6, so be aware! Something to consider when buying larger capacity cards: if you fill up a 4GB or 8GB card with RAW files, it will take much longer to download the images than a faster (133x or 150x) 2GB or 4GB SD card.

That's why I am still using those 133x SD cards...

Often when I go to do a shoot, it's at least 4GB or more of RAW files, so the speed is worth it to me.

Note that Lexar is releasing SDHC cards that actually disclose the write speed: Lexar – Flash Memory Secure Digital Cards – SDHC Professional
There may be others following this example, but I thought one example would be good to show folks.

My intent is not to downplay anyone's good find or suggest they not buy the cheaper cards, but to educate folks on the memory card speeds. You pay for speed and quality of the card's plastics, every time. I use my cards a lot, and my experience is that cheaper cards have a higher failure rate (lock tab, plastics, etc.).

Currently my experience is at a 75% failure rate for the cheaper cards...

and 0% failure for the better quality cards...

Cheers,
Marc

Last edited by Marc Langille; 02-02-2008 at 08:59 AM. Reason: clarification

Peter Zack · 02-01-2008, 08:22 PM

Good advice Marc. I've learned that lesson the hard way myself with cheaper cards that crap out in 6 months. Extreme III's for me from now on and not a single issue.

cajuncutter · 02-01-2008, 08:55 PM

Good advice. At first I wanted to get the 8 gig cards. I found some on sale and then I came across the Extreme III deal and could not pass. After shooting with my camera for the first time last night and this evening I can see there is no way a novice like me will over load 3 4 gig cards. It is also nice to have a card for different occasions. I took pictures of our family last night and simply swaped cards and took pictures at the neighbors kids b-day party. This way I don't have it all mixed up on one card.

stewart_photo · 02-01-2008, 09:49 PM

Originally posted by 35mmfilm_user

For the newcomers:

The Class # refers to the card's ...(snip)... A Class 6 SDHC card is the equivalent of ...(snip)...

Many people are confused about the card ratings, Marc. There are currently two speed ratings for SD cards, the minimum sustainable write speeds (noted by the class) and the maximum data transfer speeds (noted by the "x" factor).

The current SD Card Association (SDA) specifications mandate that all SD and SDHC cards be rated by their minimum sustainable write speeds of 2 MB/s (Class 2), 4 MB/s (Class 4), and 6 MB/s (Class 6), and maximum data transfer speeds of 0.9 MB/s (6x), 6.0 MB/s (40x), 10.0 MB/s (66x), and 20.0 MB/s (133x).

Most manufacturers now comply with this specification by listing both ratings (not always on the card itself, which is fine), but there are still exceptions (which should probably be avoided at this point). Likewise, some manufacturers list non-standard speed ratings (155x, etc) not tested or approved by the SDA board (hence should probably also be avoided as well).

stewart

SpecialK · 02-01-2008, 10:01 PM

Quote:

Something to consider when buying larger capacity cards: if you fill up a 4GB or 8GB card with RAW files, it will take much longer to download the images than a faster (133x or 150x) 2GB or 4GB SD card.

I do something else while downloading and so that has no real effect on my workflow.

Also, I suggest using smaller cards, say 1 or 2 mb, rather than bigger cards. Though you have to change them more frequently, you reduce the risk of losing all your images due to one card failure.

nosnoop · 02-02-2008, 12:18 AM

The difference is not SDHC vs SD, both have slow and fast card. As Stewart said, the Class rating is the minimum guaranteed sustained write speed. If you want to know the real speed, you have to check the specs (though only a few companies publish such specs) or check out those reviews/benchmark test.

This web site is a good reference:
CARDSPEED - Card Readers and Memory Cards

For the fast SDHC card, I would stick with SanDisk Extreme III or ATP Pro Max.

Jasvox · 02-02-2008, 01:50 AM

Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem.

**Marc Langille** · 02-02-2008, 07:05 AM

Originally posted by stewart_photo

Many people are confused about the card ratings, Marc. There are currently two speed ratings for SD cards, the minimum sustainable write speeds (noted by the class) and the maximum data transfer speeds (noted by the "x" factor).

The current SD Card Association (SDA) specifications mandate that all SD and SDHC cards be rated by their minimum sustainable write speeds of 2 MB/s (Class 2), 4 MB/s (Class 4), and 6 MB/s (Class 6), and maximum data transfer speeds of 0.9 MB/s (6x), 6.0 MB/s (40x), 10.0 MB/s (66x), and 20.0 MB/s (133x).

Most manufacturers now comply with this specification by listing both ratings (not always on the card itself, which is fine), but there are still exceptions (which should probably be avoided at this point). Likewise, some manufacturers list non-standard speed ratings (155x, etc) not tested or approved by the SDA board (hence should probably also be avoided as well).

stewart

Thanks Stewart for the links, further explanation, and the updated information!

Originally posted by nosnoop

The difference is not SDHC vs SD, both have slow and fast card. As Stewart said, the Class rating is the minimum guaranteed sustained write speed. If you want to know the real speed, you have to check the specs (though only a few companies publish such specs) or check out those reviews/benchmark test.

This web site is a good reference:
CARDSPEED - Card Readers and Memory Cards

For the fast SDHC card, I would stick with SanDisk Extreme III or ATP Pro Max.

I am aware of that (fast and slow cards), and this is a good clarification for others to read. Thank you for the link. That's why I stick with the Lexar Professional 133x SD cards, because they guarantee a minimum read AND write of 20MB/sec., compared to many SDHC cards that initially did NOT disclose the minimum write speeds, just a class #.

I feel (IMO) that's not very forthcoming by manufacturers on the specs of the card. I think you can answer why more than several manufacturers don't advertise the actual speeds on the cards. IMO, a consumer should be able to look at the product and know what they are buying, not some cryptic class number assignment. Then they apply the word "Turbo" or some other marketing gimmick.

The point of my post has worked - everyone contributing additional information on anything I've missed. This only serves to educate newcomers or folks who've not paid attention to the reality of card speeds. For many, the speed may not matter... for some, it might matter a lot - hence my specific comment in my original post.

Again, many thanks to everyone who posted - this is very valuable information!!

Regards,
Marc

**Marc Langille** · 02-02-2008, 07:21 AM

Originally posted by Jasvox

Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem.

I disagree: the Lexar Pro 133x SD cards were $5 more than standard 133x SD cards when I bought them. Hardly 2-3x the price... but much better plastics and able to withstand heavier use. The Lexar cards do not even flex under moderate pressure. To be honest, I dislike even mentioning any of this, but I am only relaying my experience with the cards - I am not a fan-boy of Lexar....

When I am downloading 500-800 RAW images from a weekend of shooting, then the speed is important to me. I've never said that people need to or have to buy the better cards - please re-read my original post...

Cheers,
Marc

Crescent City · 02-02-2008, 07:24 AM

Stewart, that is the clearest explanation of card ratings I have read. Thanks for clearing things up for me. I also wanted to add that if one is in the market for a card capable of a fast data transfer, then your reader is just as important as the card. Lexar makes a UDMA firewire reader for SD and a UDMA dual slot, SD and CF usb reader. I have know idea what UDMA is or does, but purportedly it is extremely fast. Charlie

Jun Park · 02-02-2008, 07:55 AM

Originally posted by 35mmfilm_user

I disagree: the Lexar Pro 133x SD cards were $5 more than standard 133x SD cards when I bought them. Hardly 2-3x the price... but much better plastics and able to withstand heavier use. The Lexar cards do not even flex under moderate pressure. To be honest, I dislike even mentioning any of this, but I am only relaying my experience with the cards - I am not a fan-boy of Lexar....

When I am downloading 500-800 RAW images from a weekend of shooting, then the speed is important to me. I've never said that people need to or have to buy the better cards - please re-read my original post...

Cheers,
Marc

I also agree with Marc about buying better quality cards. I do a few weddings, banquets, etc. and I am not going to risk the loss of 2 GB of pictures just to save a couple of bucks. I have been using ATP ProMax and Sandisk Extreme III cards for the important stuff. I also bought a couple of Transcend 150x cards because they were cheap and I've had retire one from regular use because I will occasionally get an error.

Jun Park · 02-02-2008, 07:59 AM

Originally posted by Jasvox

Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem.

I buy the fastest cards I can afford because when you fill up a card, you can't change out to a new card until the camera is finished writing to the current card. And if you're in the middle of an event, the few seconds can seem like an eternity!

joelw135 · 02-02-2008, 08:44 AM

I have been using Transcend 150x 2gb cards for a long time without a failure, I have also used PQ1 8gb SDHC cards also without a problem. The only card that ever failed on me was a SanDisc card. So in other words my less expensive cards have done better than my more expensive Extreme III card did. I honelty feel as some reviewers do that falsh memory is at the point that the failure rate is as good or as bad as any other card. Where people come up with facts about failure rates is a mystery to me.

**Marc Langille** · 02-02-2008, 09:07 AM

Originally posted by joelw135

have been using Transcend 150x 2gb cards for a long time without a failure<snip>
Where people come up with facts about failure rates is a mystery to me.

Hi Joel,

I have heard many good things about the Transcend cards. Thank you for taking the time to post that information!

Regarding failures: please re-read the OP. That is my experience with the failure rates on cheaper cards - and I clearly stated that they were hardware failures, not the memory itself going bad.

I never said it was across the board, so I've clarified that in the original post - that it is my experience. It's not some thing I "came up with"...

Regards,
Marc

Jasvox · 02-02-2008, 10:42 AM

Marc, That's a deal if you got that much more for only $5 more. Here in Greece, it's a very different story. The high speed cards such as the Extreme III, which is about all you can find here, is very much more expensive that the standard onces I mentioned earlier. I know prices are falling every month and it may not a big deal, but last year when the high speed 2 gig cards were over 75 euro (Extreme III), I picked up 2 Kingston standard 2 gig cards for 30 euro each. I think today, the prices are a very different story than that of even 12 months ago with these cards.

Jason

02-01-2008, 08:14 PM	#1
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,708	What the SDHC "Class #" means... be aware! For the newcomers: The Class # refers to the card's throughput in MB/sec. A Class 6 SDHC card is the equivalent of a 40x write speed (6 MB/sec.). The majority of SDHC cards are NOT any faster than Class 6, so be aware! Something to consider when buying larger capacity cards: if you fill up a 4GB or 8GB card with RAW files, it will take much longer to download the images than a faster (133x or 150x) 2GB or 4GB SD card. That's why I am still using those 133x SD cards... Often when I go to do a shoot, it's at least 4GB or more of RAW files, so the speed is worth it to me. Note that Lexar is releasing SDHC cards that actually disclose the write speed: Lexar – Flash Memory Secure Digital Cards – SDHC Professional There may be others following this example, but I thought one example would be good to show folks. My intent is not to downplay anyone's good find or suggest they not buy the cheaper cards, but to educate folks on the memory card speeds. You pay for speed and quality of the card's plastics, every time. I use my cards a lot, and my experience is that cheaper cards have a higher failure rate (lock tab, plastics, etc.). Currently my experience is at a 75% failure rate for the cheaper cards... and 0% failure for the better quality cards... Cheers, Marc Last edited by Marc Langille; 02-02-2008 at 08:59 AM. Reason: clarification

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02-01-2008, 08:22 PM	#2
Peter Zack Pentaxian Moderator Emeritus Join Date: May 2007 Location: Edmonton Alberta, Canada Photos: Gallery \| Albums Posts: 10,643	Good advice Marc. I've learned that lesson the hard way myself with cheaper cards that crap out in 6 months. Extreme III's for me from now on and not a single issue.

02-01-2008, 08:55 PM	#3
cajuncutter Senior Member Join Date: Dec 2007 Location: Louisiana Posts: 243	Good advice. At first I wanted to get the 8 gig cards. I found some on sale and then I came across the Extreme III deal and could not pass. After shooting with my camera for the first time last night and this evening I can see there is no way a novice like me will over load 3 4 gig cards. It is also nice to have a card for different occasions. I took pictures of our family last night and simply swaped cards and took pictures at the neighbors kids b-day party. This way I don't have it all mixed up on one card.

02-01-2008, 09:49 PM	#4
stewart_photo Veteran Member Join Date: Apr 2007 Location: Heidelberg, Germany Posts: 1,864	Originally posted by 35mmfilm_user For the newcomers: The Class # refers to the card's ...(snip)... A Class 6 SDHC card is the equivalent of ...(snip)... Many people are confused about the card ratings, Marc. There are currently two speed ratings for SD cards, the minimum sustainable write speeds (noted by the class) and the maximum data transfer speeds (noted by the "x" factor). The current SD Card Association (SDA) specifications mandate that all SD and SDHC cards be rated by their minimum sustainable write speeds of 2 MB/s (Class 2), 4 MB/s (Class 4), and 6 MB/s (Class 6), and maximum data transfer speeds of 0.9 MB/s (6x), 6.0 MB/s (40x), 10.0 MB/s (66x), and 20.0 MB/s (133x). Most manufacturers now comply with this specification by listing both ratings (not always on the card itself, which is fine), but there are still exceptions (which should probably be avoided at this point). Likewise, some manufacturers list non-standard speed ratings (155x, etc) not tested or approved by the SDA board (hence should probably also be avoided as well). stewart

02-01-2008, 10:01 PM	#5
SpecialK Pentaxian Join Date: Dec 2006 Location: So California Photos: Gallery Posts: 16,480	Quote: Something to consider when buying larger capacity cards: if you fill up a 4GB or 8GB card with RAW files, it will take much longer to download the images than a faster (133x or 150x) 2GB or 4GB SD card. I do something else while downloading and so that has no real effect on my workflow. Also, I suggest using smaller cards, say 1 or 2 mb, rather than bigger cards. Though you have to change them more frequently, you reduce the risk of losing all your images due to one card failure.

02-02-2008, 12:18 AM	#6
nosnoop Veteran Member Join Date: Feb 2007 Posts: 1,299	The difference is not SDHC vs SD, both have slow and fast card. As Stewart said, the Class rating is the minimum guaranteed sustained write speed. If you want to know the real speed, you have to check the specs (though only a few companies publish such specs) or check out those reviews/benchmark test. This web site is a good reference: CARDSPEED - Card Readers and Memory Cards For the fast SDHC card, I would stick with SanDisk Extreme III or ATP Pro Max.

02-02-2008, 01:50 AM	#7
Jasvox Veteran Member Join Date: Oct 2007 Location: Melbourne, Australia Posts: 3,107	Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem.

02-02-2008, 07:05 AM	#8
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,708 Original Poster	Originally posted by stewart_photo Many people are confused about the card ratings, Marc. There are currently two speed ratings for SD cards, the minimum sustainable write speeds (noted by the class) and the maximum data transfer speeds (noted by the "x" factor). The current SD Card Association (SDA) specifications mandate that all SD and SDHC cards be rated by their minimum sustainable write speeds of 2 MB/s (Class 2), 4 MB/s (Class 4), and 6 MB/s (Class 6), and maximum data transfer speeds of 0.9 MB/s (6x), 6.0 MB/s (40x), 10.0 MB/s (66x), and 20.0 MB/s (133x). Most manufacturers now comply with this specification by listing both ratings (not always on the card itself, which is fine), but there are still exceptions (which should probably be avoided at this point). Likewise, some manufacturers list non-standard speed ratings (155x, etc) not tested or approved by the SDA board (hence should probably also be avoided as well). stewart Thanks Stewart for the links, further explanation, and the updated information! Originally posted by nosnoop The difference is not SDHC vs SD, both have slow and fast card. As Stewart said, the Class rating is the minimum guaranteed sustained write speed. If you want to know the real speed, you have to check the specs (though only a few companies publish such specs) or check out those reviews/benchmark test. This web site is a good reference: CARDSPEED - Card Readers and Memory Cards For the fast SDHC card, I would stick with SanDisk Extreme III or ATP Pro Max. I am aware of that (fast and slow cards), and this is a good clarification for others to read. Thank you for the link. That's why I stick with the Lexar Professional 133x SD cards, because they guarantee a minimum read AND write of 20MB/sec., compared to many SDHC cards that initially did NOT disclose the minimum write speeds, just a class #. I feel (IMO) that's not very forthcoming by manufacturers on the specs of the card. I think you can answer why more than several manufacturers don't advertise the actual speeds on the cards. IMO, a consumer should be able to look at the product and know what they are buying, not some cryptic class number assignment. Then they apply the word "Turbo" or some other marketing gimmick. The point of my post has worked - everyone contributing additional information on anything I've missed. This only serves to educate newcomers or folks who've not paid attention to the reality of card speeds. For many, the speed may not matter... for some, it might matter a lot - hence my specific comment in my original post. Again, many thanks to everyone who posted - this is very valuable information!! Regards, Marc

02-02-2008, 07:21 AM	#9
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,708 Original Poster	Originally posted by Jasvox Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem. I disagree: the Lexar Pro 133x SD cards were $5 more than standard 133x SD cards when I bought them. Hardly 2-3x the price... but much better plastics and able to withstand heavier use. The Lexar cards do not even flex under moderate pressure. To be honest, I dislike even mentioning any of this, but I am only relaying my experience with the cards - I am not a fan-boy of Lexar.... When I am downloading 500-800 RAW images from a weekend of shooting, then the speed is important to me. I've never said that people need to or have to buy the better cards - please re-read my original post... Cheers, Marc

02-02-2008, 07:24 AM	#10
Crescent City Inactive Account Join Date: Oct 2007 Location: New Orleans, La Posts: 55	Stewart, that is the clearest explanation of card ratings I have read. Thanks for clearing things up for me. I also wanted to add that if one is in the market for a card capable of a fast data transfer, then your reader is just as important as the card. Lexar makes a UDMA firewire reader for SD and a UDMA dual slot, SD and CF usb reader. I have know idea what UDMA is or does, but purportedly it is extremely fast. Charlie

02-02-2008, 07:55 AM	#11
Jun Park Senior Member Join Date: Nov 2006 Location: Pensacola, FL Posts: 182	Originally posted by 35mmfilm_user I disagree: the Lexar Pro 133x SD cards were $5 more than standard 133x SD cards when I bought them. Hardly 2-3x the price... but much better plastics and able to withstand heavier use. The Lexar cards do not even flex under moderate pressure. To be honest, I dislike even mentioning any of this, but I am only relaying my experience with the cards - I am not a fan-boy of Lexar.... When I am downloading 500-800 RAW images from a weekend of shooting, then the speed is important to me. I've never said that people need to or have to buy the better cards - please re-read my original post... Cheers, Marc I also agree with Marc about buying better quality cards. I do a few weddings, banquets, etc. and I am not going to risk the loss of 2 GB of pictures just to save a couple of bucks. I have been using ATP ProMax and Sandisk Extreme III cards for the important stuff. I also bought a couple of Transcend 150x cards because they were cheap and I've had retire one from regular use because I will occasionally get an error.

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02-02-2008, 07:59 AM	#12
Jun Park Senior Member Join Date: Nov 2006 Location: Pensacola, FL Posts: 182	Originally posted by Jasvox Cheap cards such as Kingston or Dane work just fine, no use spending 2-3 times as much on something with a fancy label. I can stand waiting an extra minute when downloading 100+ photos. I have four 2 gig cards, standard speeds, never any problem. I buy the fastest cards I can afford because when you fill up a card, you can't change out to a new card until the camera is finished writing to the current card. And if you're in the middle of an event, the few seconds can seem like an eternity!

02-02-2008, 08:44 AM	#13
joelw135 Senior Member Join Date: Sep 2007 Location: Kendall Park, NJ Photos: Gallery Posts: 143	I have been using Transcend 150x 2gb cards for a long time without a failure, I have also used PQ1 8gb SDHC cards also without a problem. The only card that ever failed on me was a SanDisc card. So in other words my less expensive cards have done better than my more expensive Extreme III card did. I honelty feel as some reviewers do that falsh memory is at the point that the failure rate is as good or as bad as any other card. Where people come up with facts about failure rates is a mystery to me.

02-02-2008, 09:07 AM	#14
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,708 Original Poster	Originally posted by joelw135 have been using Transcend 150x 2gb cards for a long time without a failure<snip> Where people come up with facts about failure rates is a mystery to me. Hi Joel, I have heard many good things about the Transcend cards. Thank you for taking the time to post that information! Regarding failures: please re-read the OP. That is my experience with the failure rates on cheaper cards - and I clearly stated that they were hardware failures, not the memory itself going bad. I never said it was across the board, so I've clarified that in the original post - that it is my experience. It's not some thing I "came up with"... Regards, Marc

02-02-2008, 10:42 AM	#15
Jasvox Veteran Member Join Date: Oct 2007 Location: Melbourne, Australia Posts: 3,107	Marc, That's a deal if you got that much more for only $5 more. Here in Greece, it's a very different story. The high speed cards such as the Extreme III, which is about all you can find here, is very much more expensive that the standard onces I mentioned earlier. I know prices are falling every month and it may not a big deal, but last year when the high speed 2 gig cards were over 75 euro (Extreme III), I picked up 2 Kingston standard 2 gig cards for 30 euro each. I think today, the prices are a very different story than that of even 12 months ago with these cards. Jason