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Old Apr 30, 2010, 7:30 AM   #11
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Class rating is irrelevant as it only indicates that a given card can reach that speed, not sustain it.
Actually, the Speed Class Ratings are for minimum sustained write speeds. The X speed ratings are for maximum instantaneous read speeds.

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Also, card manufacturers are the one who put that rating on the card..
That's true, unfortunately.

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Unfortunately, it's not that easy to find real benchmarks posted on the net for all the cards out there. This test lists a few though.
Actually, I prefer this one. It covers CF as well as SD Cards.
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Old Apr 30, 2010, 8:06 AM   #12
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This is a good site for benchmarks (although they don't test all cards, they have a pretty good collection of tests now).

http://www.hjreggel.net/cardspeed/index.html

But, you also have to take the camera into consideration, as some cards work better than others in a given camera model due to a variety of factors (block sizes, access delay, processing bottlenecks elsewhere, supported transfer modes, etc.).

For example, here are some of their tests for UDMA CF cards (although they haven't tested some of the newer 600x cards yet):

http://www.hjreggel.net/cardspeed/in...cs_udmacf.html

Here are some SDHC card tests:

http://www.hjreggel.net/cardspeed/sp...cards-sdc.html

If you select a card type here, you can see tests they've done. Click the link to Switch to "Frame View" and you'll see more menu choices on the left side of the page (and they also have an archive section for older cards).

http://www.hjreggel.net/cardspeed/speed-by-cards.html

They also have tests of newer Pro-HG Duo cards for Sony users wanting faster cards (as this card type is *much* faster than Sandisk 30MB/Second SDHC cards in newer Sony dSLR models that can use either SDHC or MS Pro Duo, and card reader tests also show how much faster this memory type is compared to SDHC).

http://www.hjreggel.net/cardspeed/sp...cards-msh.html
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Old Apr 30, 2010, 5:02 PM   #13
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Actually, the Speed Class Ratings are for minimum sustained write speeds.
Incorrect. Speed class ratings measure the minimum write speed based on "the best fragmented state where no memory unit is occupied". They do not reflect sustained speeds.

Here is a quote directly from the SD Association:

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The SD Association has established a specification that rates the minimum data transfer both SD/SDHC cards and SD/SDHC host products. The speed rate specifications were established based on the request from movie and video companies. Video recording requires certain writing speeds when recording the data onto an SD card. The SD Speed Class standardized the spec for both card and host devices in order to guarantee minimum writing speeds.
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Actually, I prefer this one. It covers CF as well as SD Cards.
It's great that he tested them with cameras for our needs here, but it looks like his tests only measure 1 file (averaged over 3 attempts) rather than sustained speed. He also simply times the transfer rather than using a more precise measurement.
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Old Apr 30, 2010, 5:11 PM   #14
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Actually, if you look a camera specific tests, Rob Galbraith takes enough photos to fill a camera's internal buffer (which varies by camera model), then times how long it takes the camera to finish emptying that buffer to compute transfer speeds (using the "busy" light to determine it). He uses both raw and jpeg files for tests.

If you look at an individual camera's test, he'll discuss how many photos he used for it. Here's an example (see the notes at the top of the page):

http://www.robgalbraith.com/bins/cam...?cid=6007-9550

That's usually a pretty good way to test a card's performance in a specific camera model (make sure you take enough photos to fill the camera's internal buffer, then time how long it takes to empty that buffer from the time the last photo was taken).

That way, you're testing how well a given card model works in a given camera model (using both raw and jpeg tests, as file sizes are different between them and you will often see performance differences due to other factors like camera processing bottlenecks and delays; and how well a given card "meshes" with the way a specific camera model is writing to it).

IOW, it's a more realistic way of telling how well a given card works in a given camera (rather than just looking at how a card may perform in a card reader, which doesn't take the camera it's being used with into consideration).
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Old Apr 30, 2010, 7:11 PM   #15
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Actually, the Speed Class Ratings are for minimum sustained write speeds. The X speed ratings are for maximum instantaneous read speeds.
Incorrect. Speed class ratings measure the minimum write speed based on "the best fragmented state where no memory unit is occupied". They do not reflect sustained speeds.

Here is a quote directly from the SD Association:
Quote:
The SD Association has established a specification that rates the minimum data transfer both SD/SDHC cards and SD/SDHC host products. The speed rate specifications were established based on the request from movie and video companies. Video recording requires certain writing speeds when recording the data onto an SD card. The SD Speed Class standardized the spec for both card and host devices in order to guarantee minimum writing speeds.
Read the actual specification. On page 69, it states:

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The Classes are defined so that AV application, such as MPEG2 recording, can support SD card device. The performance of a Speed Class 2 card shall be higher than performance curve 2. It is defined for standard TV image quality; approximately 2MB/sec performance will be required. The performance of a Speed Class 4 card shall be higher than performance curve 4. Speed Class 4 is defined for HD video quality; approximately 4MB/sec performance will be required. (Emphasis mine. -TCav)
In other words, under the stated circumstances, the write speed of a Class 2 Card cannot be less than approximately 2MB/sec ever. And the write speed of a Class 4 Card cannot be less than approximately 4MB/sec ever. That means "sustained", as in an SD video signal can be recorded onto a Class 2 Card without breakup until the card is full. Similarly, an HD video signal can be recorded onto a Class 4 Card without breakup until the card is full. Hence my use of the word "sustained."

Note that this is only for recording video. If you'll be recording audio as well, then a Class 4 Card can't record HD video and audio without breaking up, so you should go to the next higher class to get uninterrupted video and audio.
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Old Feb 17, 2013, 11:47 AM   #16
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Default SD Upgrade to SDHC is Available

My 5+ year old laptop has a built in SD card reader. When I started using SDHC cards I was under the impression that the built in reader would not be able to read the higher capacity cards.

A couple of days ago, on a whim, I put an SDHC card into the laptop and much to my surprise it was able to recognize and download the JPEG and Raw mages on the card.

I did some Google searches and found that updates from Microsoft seems to have dealt with the problem. A 2007 update, KB936825, was to allow for the use of SDHC cards and a 2008 update, KB975823 allowed for use of cards greater than 32GB.

I checked the update list on the laptop and these have been downloaded through the regular update process so it appears my built in SD reader is now capable of reading SDHC cards also.

Wondering if anyone else has noticed the same.

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Old Feb 17, 2013, 12:58 PM   #17
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The problem isn't neccessarily with Windows but with the hardware in the reader. Readers in Laptops (or any computer) tend to be more up-to-date than the stand-alone readers that are available on the market at about the same time.
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Old Feb 18, 2013, 8:28 AM   #18
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The problem isn't neccessarily with Windows but with the hardware in the reader. Readers in Laptops (or any computer) tend to be more up-to-date than the stand-alone readers that are available on the market at about the same time.

I was under the impression that my built in card reader could only read SD cards and not SDHC (labelling on the computer only indicates SD - I have seen other laptops/desktops where the card slot has the SD and SDHC labelling). Regardless, it is a bonus to now have the convenience of using the built in reader.

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