-
Welcome to the new forums! Please read this first. For known issues we are working to resolve, click here.
Sandisk Ultra II sdhc different class (class 2,4,6)
- Thread starter ron1946
- Start date
153957Photography
Forum Enthusiast
The speed! that is exactly what those classes are.
Well they are the minimum that the card should be able to sustain until full.
So a Class 2 card 'MUST' be able to sustain at least a read/write speed of 2 MB/s,
and Class 4 4 MB/s, and 6 .. you guessed it 6 MB/s.
This doesn't mean that they cant go faster, just that that should be the minimum.
To bad that there aren't any higher classes yet...
some info...
http://en.wikipedia.org/wiki/Secure_Digital_card#SDHC
--
(also Time-Lapse photography)
Well they are the minimum that the card should be able to sustain until full.
So a Class 2 card 'MUST' be able to sustain at least a read/write speed of 2 MB/s,
and Class 4 4 MB/s, and 6 .. you guessed it 6 MB/s.
This doesn't mean that they cant go faster, just that that should be the minimum.
To bad that there aren't any higher classes yet...
some info...
http://en.wikipedia.org/wiki/Secure_Digital_card#SDHC
--
- 153957 Photography -
(also Time-Lapse photography)
Michael Meissner
Forum Pro
Well for SDHC there aren't higher classes (some compact flash cards can go much faster).
It also depends on the speed of the camera or reader. If you have a camera that writes slowly, putting in a faster card won't help much.
Ron,
There have been three different versions of the SanDisk Ultra II SDHC cards that were available. The original version was rated at 10 MB/s read and 9 MB/s write. The second, revised version (which was available for only a few months in 2008)was rated at 15 MB/s read and write. The currently shipping version is rated at 15 MB/s read, but only 9 MB/s write (that information is found on the back of the package in fine print; the front of the package claims only the 15 MB/s figure). Previous versions of the Ultra II were Class 4 cards; the currently shipping version is only Class 2.
Hope this helps.
There have been three different versions of the SanDisk Ultra II SDHC cards that were available. The original version was rated at 10 MB/s read and 9 MB/s write. The second, revised version (which was available for only a few months in 2008)was rated at 15 MB/s read and write. The currently shipping version is rated at 15 MB/s read, but only 9 MB/s write (that information is found on the back of the package in fine print; the front of the package claims only the 15 MB/s figure). Previous versions of the Ultra II were Class 4 cards; the currently shipping version is only Class 2.
Hope this helps.
BG454
Veteran Member
The details of the SD "Class" speed rating system are here:
http://www.sdcard.org/developers/tech/speed_class/
The "Class" speed is a minimum rating, of 2,4 or 6 MB/sec for Class 2,4 & 6 respectively.
At up to 15MB/sec read/write speed (Sandisk figures), the Sandisk UltraII comfortably exceeds even "Class 6" minimum speed, so Sandisk are being very modest in calling it "Class 2."
IMHO this "Class" rating system seems to cause more confusion than it solves. As cards speeds (inevitably) increase, there will come a time when all cards exceed "Class 6" ratings, yet show a huge range of variation between brands. For those that really care, a study of the manufacturers specifications for each type of card is more useful than a so-called "minimum" speed rating.
--
http://www.sdcard.org/developers/tech/speed_class/
The "Class" speed is a minimum rating, of 2,4 or 6 MB/sec for Class 2,4 & 6 respectively.
At up to 15MB/sec read/write speed (Sandisk figures), the Sandisk UltraII comfortably exceeds even "Class 6" minimum speed, so Sandisk are being very modest in calling it "Class 2."
IMHO this "Class" rating system seems to cause more confusion than it solves. As cards speeds (inevitably) increase, there will come a time when all cards exceed "Class 6" ratings, yet show a huge range of variation between brands. For those that really care, a study of the manufacturers specifications for each type of card is more useful than a so-called "minimum" speed rating.
--
Expert Photo Recovery
Well-known member
Hi,
First, at least some of the manufacturer speed ratings are showing just the higher speed (typically the read speed); whereas a class X card must be capable of reading and writing at that speed of X MB/s. At least one manufacturer has some cards with very different read & write speeds, and the "headline" speed is the higher one, of course.
Second, and perhaps less well known, is that the manufacturer's speed test will be done using a test (which could be different for different manufacturers e.g. HD Bench, HDTach etc.) that is going to show as close as they can get to the maximum speed for the card. This will mean doing large block size sequential reads & writes, with no filesystem (i.e. with "raw" I/Os - which are not related to raw photo files). Yet cameras are always writing to a filesystem on the card, and having to do small non-sequential I/Os to update the FAT, as well as writing the data for each image.
SanDisk are quoted here as saying that the PC motherboard type & USB controller (as well as the card reader, of course) also have an effect on the "headline" test result:
http://www.robgalbraith.com/bins/content_page.asp?cid=7-6459-7253
Due to the work done by the SD card controller for wear-levelling, and the internal card architecture differences in different makes & models of cards (single vs. multiple NAND channels, SLC vs. MLC, erase block size, FAT cluster vs. erase block alignment differences, and many other things that we'll never know in the hidden proprietary details of the card controllers) the overall data transfer speed when doing smaller I/Os to a filesystem (as done by a camera), can be very different to the speed with large raw sequential I/Os, which were used to get that "headline" manufacturer's speed result.
Hope that helps to explain some of the reasons for the difference in quoted speed ratings that you mentioned.
Regards,
--
Sam
Confusingly, a card can be both capable of 15MB/s and only class 2 (and not class 4 or faster), as the tests in each case, are very different. If Sandisk could have called it a class 4 or class 6 card, I expect they would have done that...
First, at least some of the manufacturer speed ratings are showing just the higher speed (typically the read speed); whereas a class X card must be capable of reading and writing at that speed of X MB/s. At least one manufacturer has some cards with very different read & write speeds, and the "headline" speed is the higher one, of course.
Second, and perhaps less well known, is that the manufacturer's speed test will be done using a test (which could be different for different manufacturers e.g. HD Bench, HDTach etc.) that is going to show as close as they can get to the maximum speed for the card. This will mean doing large block size sequential reads & writes, with no filesystem (i.e. with "raw" I/Os - which are not related to raw photo files). Yet cameras are always writing to a filesystem on the card, and having to do small non-sequential I/Os to update the FAT, as well as writing the data for each image.
SanDisk are quoted here as saying that the PC motherboard type & USB controller (as well as the card reader, of course) also have an effect on the "headline" test result:
http://www.robgalbraith.com/bins/content_page.asp?cid=7-6459-7253
Due to the work done by the SD card controller for wear-levelling, and the internal card architecture differences in different makes & models of cards (single vs. multiple NAND channels, SLC vs. MLC, erase block size, FAT cluster vs. erase block alignment differences, and many other things that we'll never know in the hidden proprietary details of the card controllers) the overall data transfer speed when doing smaller I/Os to a filesystem (as done by a camera), can be very different to the speed with large raw sequential I/Os, which were used to get that "headline" manufacturer's speed result.
Hope that helps to explain some of the reasons for the difference in quoted speed ratings that you mentioned.
Regards,
--
Sam
BG454
Veteran Member
If they'd called the Ultra II "Class 6" then what could they call the Extreme series of cards, which are even faster? (and are rated "Class 6")
IMHO the "Class" system of SDHC speed rating is a disaster, and only serves to confuse the uninitiated. Far better to read the manufacturers spec, or a reliable site like the Rob Galbraith reviews, to find out how fast the cards really perform.
--
technicsplayer.
Senior Member
Ultra 2 SD can easily do 2 MB/s continuous for unlimited video, they call it class 2 purely for marketing reasons, so they can charge higher for Extremes, the whole thing designed for punters who don't know anything about the specs and think they are improving their point and shoots by buying super fast cards when their pocket cam can't even write at 1/4 of the card speed 
Expert Photo Recovery
Well-known member
Hi,
). Is that what you were suggesting?
If that were true, then why are some 2GB Ultra II cards marked as Class 4:
http://www.sandisk.com/Products/Item (1164)-SDSDH-002G-A11-SanDisk_Ultra_II_SD_2GB.aspx
and larger ones as Class 2?
http://www.sandisk.com/Products/Item (2201)-SDSDRH-004G-A11-SanDisk_Ultra_II_SDHC_4GB_High_Performance_Card.aspx
Surely they would mark them all as Class 2, if they're trying to make them appear slower than they actually are? (I've only seen the larger capacity Class 2 Ultra II cards here recently, but the photos above show that Class 4 Ultra II cards exist.)
As you say, for people with P&S cameras, there's likely to be no measurable benefit in the camera, to using the faster cards.
An interesting write-up on this subject is on Hans-Jürgen Reggel's "Cardspeed" site:
http://www.hjreggel.net/cardspeed/special-sd.html
Regards,
--
Sam
Card speed testing isn't my speciality, but if you're suggesting that the Ultra II cards marked as Class 2 could actually pass a Class 4 or 6 speed test, and that they are deliberately not marked as such to make more people buy the Extreme III, then I personally doubt it (but that's just IMHO
). Is that what you were suggesting?If that were true, then why are some 2GB Ultra II cards marked as Class 4:
http://www.sandisk.com/Products/Item (1164)-SDSDH-002G-A11-SanDisk_Ultra_II_SD_2GB.aspx
and larger ones as Class 2?
http://www.sandisk.com/Products/Item (2201)-SDSDRH-004G-A11-SanDisk_Ultra_II_SDHC_4GB_High_Performance_Card.aspx
Surely they would mark them all as Class 2, if they're trying to make them appear slower than they actually are? (I've only seen the larger capacity Class 2 Ultra II cards here recently, but the photos above show that Class 4 Ultra II cards exist.)
As you say, for people with P&S cameras, there's likely to be no measurable benefit in the camera, to using the faster cards.
An interesting write-up on this subject is on Hans-Jürgen Reggel's "Cardspeed" site:
http://www.hjreggel.net/cardspeed/special-sd.html
Regards,
--
Sam
Yes, when SanDisk introduced a new label style back in late 2007, it marked even the smaller-capacity SD cards with class ratings. However, the newest shipping versions of the 2GB Ultra II now no longer has a class rating. The newest versions of the "15 MB/s" Ultra II (which now come in a cardboard card with minimal plastic packaging) have a significantly slower write speed than the earlier versions of that card (packaced in a plastic package which must be cut open to get at the card): 9 MB/s write on the newer versions (as indicated in small print on the back of the actual cardboard package) versus 15 MB/s read/write listed at the front of the earlier versions of that card (which was available for just a few months in 2008). All currently shipping versions of the Ultra II have only a 9 MB/s write speed rating (15 MB/s read speed rating), and the SDHC sizes are conservatively rated Class 2.
Expert Photo Recovery
Well-known member
Hi,
I hope you see my point that if they're trying to label them as "slower than they are" for some reason, then they haven't always done that.
[edited to write "Ultra II" correctly.]
Thanks,
--
Sam
Sorry, I see you had discussed this in your earlier post in this thread
I hope you see my point that if they're trying to label them as "slower than they are" for some reason, then they haven't always done that.I haven't seen any evidence that this is a conservative (rather than a correct) Class 2 speed rating. Out of interest, do you have any evidence that when running the SD speed class test (with its specific requirements for SD clock speed and I/O size etc.) that the Ultra II cards marked as Class 2 will be faster than Class 2? I haven't seen anything to show that this isn't an accurate rating on a card which is actually marked as Class 2, when doing that specific (unpublished but somewhat leaked) test.
[edited to write "Ultra II" correctly.]
Thanks,
--
Sam
technicsplayer.
Senior Member
I obviously cannot replicate the "official" class 2 speed test, but I have various versions of Ultra 2 from early 9Mb/s write to the latest ones, from 2GB to 8GB and every one of them has tested way past 2MB/s write in 1) HDtach, 2) Atto benchmark, 3) Cardtest, and 4) Flash Memory Toolkit, the programs I have tried on each one as I bought them. All these programs have slightly different test parameters, but results were consitently around the 8MB/s and above write. Only some of these test programs unformat the card so the others must be writing to fat file system and updating etc.
Expert Photo Recovery
Well-known member
Hi,
I'm not trying to convince you or anyone else that I'm right in believing Sandisk's claim - I might not be right since, as I said earlier, card benchmarking is not my speciality. However I have seen wide variations in actual card speeds between large block sequential writes and small block non-sequential writes, especially on MLC flash, with a large erase block size. That is what makes me not immediately disbelieve the Sandisk claim of Class 2 for an Ultra II card, despite its 9MB/s "headline" write speed.
I have an open mind to seeing evidence in the future, that shows Sandisk might indeed be marking their Ultra II cards as Class 2, when they are actually faster in that specific test . I just don't agree that typical benchmark program results, on standard card readers, are valid comparisons for that specific test.
Thanks for your earlier comments anyway.
Regards,
--
Sam
That's the problem we all have - and that's why I don't believe anyone has yet shown the evidence to dispute the Class 2 description from Sandisk, because any other tests are different and, IMHO, therefore give a different result. I understand that you feel differently.
In the copy of Flash Memory Toolkit that I have access to, the smallest I/O size is shown as 1MB. IMHO that's a problem in this situation, because the figures I've seen leaked for the I/O sizes in the SD speed class test are much, much smaller than that (and hence will result in slower speeds).
I'm not trying to convince you or anyone else that I'm right in believing Sandisk's claim - I might not be right since, as I said earlier, card benchmarking is not my speciality. However I have seen wide variations in actual card speeds between large block sequential writes and small block non-sequential writes, especially on MLC flash, with a large erase block size. That is what makes me not immediately disbelieve the Sandisk claim of Class 2 for an Ultra II card, despite its 9MB/s "headline" write speed.
I have an open mind to seeing evidence in the future, that shows Sandisk might indeed be marking their Ultra II cards as Class 2, when they are actually faster in that specific test . I just don't agree that typical benchmark program results, on standard card readers, are valid comparisons for that specific test.
Thanks for your earlier comments anyway.
Regards,
--
Sam
BG454
Veteran Member
Whether or not Sandisk are deliberately playing down the Class rating of their cards, I think this business confirms my earlier assertion that the "Class" rating system is confusing.
To try and establish data transfer rate standards in the ever changing world of computer development is a risky business. What seems a fast data rate today will look very slow after three or four years development of memory chips. Will the SD card association bring out "Class 8" and beyond, as memory performance increases?
According to the hjreggel website: "Please note that the Speed Class Rating is intended to be used in conjunction with SD based Video Cameras" so the whole thing is inapplicable to still cameras. In normal shooting I've never needed to wait for an Ultra II card to finish writing before I could continue, and the download to computer speed is plenty fast enough for me (and that's using the earlier 10MB/s card).
--
To try and establish data transfer rate standards in the ever changing world of computer development is a risky business. What seems a fast data rate today will look very slow after three or four years development of memory chips. Will the SD card association bring out "Class 8" and beyond, as memory performance increases?
According to the hjreggel website: "Please note that the Speed Class Rating is intended to be used in conjunction with SD based Video Cameras" so the whole thing is inapplicable to still cameras. In normal shooting I've never needed to wait for an Ultra II card to finish writing before I could continue, and the download to computer speed is plenty fast enough for me (and that's using the earlier 10MB/s card).
--
technicsplayer.
Senior Member
Hi,
My copy of Atto allows selectable transfer size down to 0.5 kB with either overlapped I/O or I/O comparison. As soon as you are up to 1kB transfers the write speed is 2 MB/s on a class2 Ultra 2 (this to fat formats which don't get unformatted by test). Doesn't prove anything but my camera does 640x480@30 unlimited which works out very close to 2MB/s write and no Ultra2 had ever dropped a frame, but that only confirms the class 2 I suppose, But unlimited continuous shoot (buffer flush) requires around 5MB/s and all the Ultra2s don't stop at that either as long as the card space holds out. Cheaper cards which have the official class 4 rating also measure slower write than the Ultra2s on the same tests with the same readers but are above 4 MB/s.
We are in agreement that without the exact test we don't know, and I could be wrong too, it's just that all the pc write tests I have ever done on all my Ultra2s are so far in advance of 2 MB/s that I just don't believe they could not pass a higher class test.
regards,
Tim Dolan
Leading Member
Based on my few examples to date. I have basically learned to ignore the class ratings for any uses I have outside of specifically using it for sustained video operation.
I do this because
Class ratings only show the fastest MINIMUM SUSTAINED rate that the card can be written to. It does not indicate the average speed nor the maximum speed of the card.
I had to learn this the hard way.
Also knowing how standards are set, it may be that the card has to maintain that speed using the standard test mechanism throughout the whole of the card's capacity. I know from experience that as you fill up most SD or CF cards they tend to slow down, so I rarely if ever fill them to capacity before clearing them. If the standard requires the whole of the card to run at that rate then it is quite possible the Ulta II, may only test out to class 2, even if indications are they go considerably faster.
For my camera's use I have discovered that it tends to max out at around 17-18Mbs so as long as I have a card at least that rated speed, I am happy with the transfer rate from the camera to the card. A minimal class 6 card is too slow for my use, I really need a class 10 or better a class 20 card to make it work for me, however, luckily most manufacturers put a maximum transfer rate rating on their card's packaging, so if they are in the 20Mbs rate or higher then I am fairly confident that for at least the first 3/4ths of the card's capacity it will sustain the transfer rate that I need.
In any case Sandisk Extreme III/30Mbs or Extreme IV cards (or equivilant) seem to be what I need right now for my 1DsMkIII.
--
Save the Model, Save the Camera, The photographer can be repaired.
I do this because
Class ratings only show the fastest MINIMUM SUSTAINED rate that the card can be written to. It does not indicate the average speed nor the maximum speed of the card.
I had to learn this the hard way.
Also knowing how standards are set, it may be that the card has to maintain that speed using the standard test mechanism throughout the whole of the card's capacity. I know from experience that as you fill up most SD or CF cards they tend to slow down, so I rarely if ever fill them to capacity before clearing them. If the standard requires the whole of the card to run at that rate then it is quite possible the Ulta II, may only test out to class 2, even if indications are they go considerably faster.
For my camera's use I have discovered that it tends to max out at around 17-18Mbs so as long as I have a card at least that rated speed, I am happy with the transfer rate from the camera to the card. A minimal class 6 card is too slow for my use, I really need a class 10 or better a class 20 card to make it work for me, however, luckily most manufacturers put a maximum transfer rate rating on their card's packaging, so if they are in the 20Mbs rate or higher then I am fairly confident that for at least the first 3/4ths of the card's capacity it will sustain the transfer rate that I need.
In any case Sandisk Extreme III/30Mbs or Extreme IV cards (or equivilant) seem to be what I need right now for my 1DsMkIII.
--
Save the Model, Save the Camera, The photographer can be repaired.
Tim Dolan
Leading Member
I forgot to mention. I have the following SD and SDHC cards for comparison
My 1GB Extreme III SD card works real well, but obviously doesn't hold a whole lot of data. The Ultra II class 4 card I have is ssssllllooooooowwwww - so slow I can't even use it for small jpegs without it limiting the buffers. The Transend 4GB class 6 card I have is slow, but useable for jpegs.
I am planning on getting an 16GB extreme III SDHC 30Mbs card in the very near future and will be able to confirm my suspicions if it works as well as I suspect it will.
--
Save the Model, Save the Camera, The photographer can be repaired.
My 1GB Extreme III SD card works real well, but obviously doesn't hold a whole lot of data. The Ultra II class 4 card I have is ssssllllooooooowwwww - so slow I can't even use it for small jpegs without it limiting the buffers. The Transend 4GB class 6 card I have is slow, but useable for jpegs.
I am planning on getting an 16GB extreme III SDHC 30Mbs card in the very near future and will be able to confirm my suspicions if it works as well as I suspect it will.
--
Save the Model, Save the Camera, The photographer can be repaired.
Keyboard shortcuts
- f
- Forum