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02-25-2009, 01:50 PM   #1
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K-m Write Speed

In the process of buying a memory card for the K-m.
Some observations.

Looking at this thread: https://www.pentaxforums.com/forums/pentax-dslr-discussion/46010-k200d-write-speed.html , the K200D write-speed is 5.5 MB/s (max.)

Same calculation from DPR's K-m review gives 10MB/s for the K-m.

It's interesting that the K-m is quite a bit faster than the K200D.

That's still slower than say the Sandisk Ultra II's speed, but getting close to it. Sandisk Extreme III's still have an advantage of uploading speed to computer.
I've been using an EIII since a consumer-grade card literally fell apart on a vacation trip. While the UII's are 'fast enough' I don't think they have the same construction.

02-25-2009, 02:16 PM   #2
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I think buffer size has something to do with performance besides wrtie-in speed.

I am not sure how fast the K10D writes in, but because of the buffer, i have no problems shooting continuously with a Sandisk III card.

And as you stated, downloading back to the desktop is really fast!
02-25-2009, 03:45 PM   #3
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No Pentax camera is made for extended "burst" shooting, so buffer flush speed should have no importance. A simple Class 6 SDHC is enough.
02-25-2009, 04:30 PM   #4
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I'd like to learn more about this as well.

It's clear that system's continous frame rate is based on the slowest of any of the variables.

If the slowest link is from buffer to card, then the buffer will allow the camera to take images at the native HW/SW rate (meaning handling the mirror, writing from and clearing the sensor, processing the image in SW, writing to the buffer, etc.) until the buffer fills. Then the rate must fall back to the buffer ==> card max.

We see this clearly as frame rates slow with as the buffer fills.

With all respect to others, I see a very noticeable difference in write speed, K10 ==> card, between an Ultra II and Extreme III.

Unless some good engineer tells me otherwise, I will assume that the faster EIII read speed (write speed as seen from the camera side) allows the buffer to drain faster and therefore take more time to fill using the Extreme III. This would therefore allow me to shoot at a higher continuous rate.

That rate is still lower than the camera's "native" rate but that's OK. I can only control my choice of camera and card.

Now .... back to the max write speed from the K2000 to the card. Any suggestions?

And for the very interested, I wonder if the sustained transfer rate is different for small JPEGs than for larger raw files. The transfer protocol and the way it's implemented may yield differing rates if there is a per-file overhead.

02-26-2009, 02:28 AM   #5
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I purchased a 2GB Sandisk Extreme III for my K-m. The price difference between that and the 2GB Ultra II was minimal, so I though extra speed might be helpful (if not at shooting, then at moving pictures from card to pc in card reader). It is also guaranteed to work in a bigger temperature range (between +85 and -25 C).

QuoteOriginally posted by glanglois Quote
And for the very interested, I wonder if the sustained transfer rate is different for small JPEGs than for larger raw files. The transfer protocol and the way it's implemented may yield differing rates if there is a per-file overhead.
On the weekend I might do some testing with different JPEGs (10, 6, 2 MP, ***, **, *) and RAW. I might also try it with an 512MB Kingstone Elite Pro to see the difference (or the lack of it) when using a slower card.
02-26-2009, 08:36 AM   #6
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QuoteOriginally posted by glanglois Quote
I'd like to learn more about this as well.

It's clear that system's continous frame rate is based on the slowest of any of the variables.

If the slowest link is from buffer to card, then the buffer will allow the camera to take images at the native HW/SW rate (meaning handling the mirror, writing from and clearing the sensor, processing the image in SW, writing to the buffer, etc.) until the buffer fills. Then the rate must fall back to the buffer ==> card max.

We see this clearly as frame rates slow with as the buffer fills.

With all respect to others, I see a very noticeable difference in write speed, K10 ==> card, between an Ultra II and Extreme III.

Unless some good engineer tells me otherwise, I will assume that the faster EIII read speed (write speed as seen from the camera side) allows the buffer to drain faster and therefore take more time to fill using the Extreme III. This would therefore allow me to shoot at a higher continuous rate.

That rate is still lower than the camera's "native" rate but that's OK. I can only control my choice of camera and card.

Now .... back to the max write speed from the K2000 to the card. Any suggestions?

And for the very interested, I wonder if the sustained transfer rate is different for small JPEGs than for larger raw files. The transfer protocol and the way it's implemented may yield differing rates if there is a per-file overhead.
Maybe something to do with the minimum write speed (Speed Class)
* Class 2: 2 MB/s - 13x
* Class 4: 4 MB/s - 26x
* Class 6: 6 MB/s - 40x

Most of the faster cards have a sufficient (claimed) maximum write speed (15MB/s+) to work with either the K200D or the K-m. (Maximum write speed is always claimed, there is no standard unlike the minimum speed which is supposed to be standardized.)

Also, it's possible for the host device (i.e. camera) to query the card for it's Speed Class to optimize the write speed. Who knows if these bodies have this function enabled.

SD Speed Class - SD Association
Secure Digital card - Wikipedia, the free encyclopedia
Secure Digital card - Wikipedia, the free encyclopedia

If the K200D is 5.5MB/s and the K-m is 10MB/s, then Class 6 card should make a difference, especially if the card is partially full and/or fragmented.

Perhaps this explain the differences you are seeing between the Ultra II and the Extreme III. I am not an expert either way, just trying to understand the numbers.

One thing that is not clear to me if the Speed Class is enabled on SD as well. I believe it is applicable to both SDHC and SD, but my Extreme III SD does not have a Speed Class marking (i.e. CLASS(6)).
02-26-2009, 09:59 AM   #7
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Why no class type on EIII ??

QuoteOriginally posted by dave9t5 Quote
Maybe something to do with the minimum write speed (Speed Class)
* Class 2: 2 MB/s - 13x
* Class 4: 4 MB/s - 26x
* Class 6: 6 MB/s - 40x

snip>


One thing that is not clear to me if the Speed Class is enabled on SD as well. I believe it is applicable to both SDHC and SD, but my Extreme III SD does not have a Speed Class marking (i.e. CLASS(6)).
As you note, class 6 is the fastest standard, at only 6 Mbps. The EIII cards are rated at 20 MB/s so it would be something like a class 20 and 133X. There is no class 20 so no class would or should be indicated on the packaging. They certainly don't want an unwary buyer thinking that their very fast EIII cards perform the same as someone else's class 6 at only one third of the speed of the EIII.

And this is why I get a bit aggravated when class six cards (at only 6 MB/s) are marketed as very high speed, fast as they get, etc. They are, at best, in the mid-range. Even the Ultra II at about 9 MB/s is 50% faster than class six.

The standards body for SD is working on those faster standards and we should, I think, see one or more of them this year. But that work may be no more than documenting the technology that's been shipping for quite a while now.
02-26-2009, 12:04 PM   #8
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The answer, via chat, from Pentax rep Michael C. is that the K2000 will make use of very fast cards. I eventually asked specifically if I needed a 20 MB/s card to get to the published fps rates. His reply was that the camera would transfer images faster with the fast card than with the slower cards.

I'm condensing the conversation and am still not absolutely sure he answered the precise question. I have both Extreme III and Ultra II so I think I'd better run my own tests - unless someone here has already done that ???

02-26-2009, 05:49 PM   #9
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QuoteOriginally posted by glanglois Quote
His reply was that the camera would transfer images faster with the fast card than with the slower cards.
Woah...and if I walk faster I go faster than the slower walkers.

I wonder if that response is in the Pentax Customer Care script.
02-26-2009, 06:33 PM   #10
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QuoteOriginally posted by glanglois Quote
As you note, class 6 is the fastest standard, at only 6 Mbps. The EIII cards are rated at 20 MB/s so it would be something like a class 20 and 133X. There is no class 20 so no class would or should be indicated on the packaging. They certainly don't want an unwary buyer thinking that their very fast EIII cards perform the same as someone else's class 6 at only one third of the speed of the EIII.

And this is why I get a bit aggravated when class six cards (at only 6 MB/s) are marketed as very high speed, fast as they get, etc. They are, at best, in the mid-range. Even the Ultra II at about 9 MB/s is 50% faster than class six.

The standards body for SD is working on those faster standards and we should, I think, see one or more of them this year. But that work may be no more than documenting the technology that's been shipping for quite a while now.
Yes, of course you are right, Sandisk does claim a minimum write speed of 20MB/s for Extreme III, I didn't notice this until now. (Although see below, reviews show it to be not quite that fast.) And "20MB/s" meets (and exceeds) the specs for for the fastest class, so it is labeled Class (6) although it is much faster.

Based on claimed minimum write speeds, we could conclude:

1. K200D (5.5MB/s) could benefit from the write speed of any Class (6) card (6MB/s), but not from any card that further exceeds Class (6).

2. K-m (10MB/s) can benefit somewhat from a the Extreme III (20MB/s) compared to an Ultra II (9MB/s). Difference should be +11% faster (=10/9).

However, that may not be the case:

Here is a review of a number of SDHC cards. The conclusion is interesting:
"...we found substantial performance differences of up to 100% in the write throughput benchmarks, where the cards delivered between 9 and 18.6 MB/s. And the speed classification didn’t help much, as some Class 4 cards delivered better write performance than some Class 6 products."

While the Extreme III is judged to be the best of the test group (along with the Lexar Professional) it's minimum write speed is only measured to be ~13MB/s, which is 35% slower than SanDisk's claim. They didn't test the Ultra II but extrapolating the data we could assume that the Ultra II also under performs compared to the claimed minimum write speed of 9MB/s.

So we could revise the second point of our conclusion:

2. K-m (10MB/s) can benefit somewhat more from a the Extreme III (~13MB/s) compared to an Ultra II (~6+MB/s). Difference should be up to 67% faster (=10/6).

Looking forward to your test results!!
02-26-2009, 06:50 PM   #11
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QuoteOriginally posted by dave9t5 Quote
One thing that is not clear to me if the Speed Class is enabled on SD as well. I believe it is applicable to both SDHC and SD, but my Extreme III SD does not have a Speed Class marking (i.e. CLASS(6)).
Actually, the Wikipedia SD Card page you linked to answers your question. Speed Class is only for SDHC cards. SD cards use the same speed grade structure as CD-ROMs, DVD-ROMs, CF, MS, etc. (40x, 66x, 133x, 150x, for example). SDHC Speed Class ratings are minimum transfer rates, while the speed graded used in rating SD cards indicate maximum transfer rates.

Sometimes, manufacturers will also advertsie a maximum transfer rate (i.e., 133x) for their SDHC cards. For example, Sandisk advertises their Extreme III cards as having a max transfer rate of 30 MB/s (200x) and Ultra II cards with a 15 MB/s max transfer rate (100x).

I'd imagine why Sandisk doesn't label their Extreme and Ultra SDHC cards with a speed class is because they don't want people to think these performance cards are equal to other, "merely standard" performing cards. Sandisk does label their standard SDHC cards (the blue ones) with Class 2 speed ratings.
02-26-2009, 09:34 PM   #12
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QuoteOriginally posted by glanglois Quote
As you note, class 6 is the fastest standard, at only 6 Mbps. The EIII cards are rated at 20 MB/s so it would be something like a class 20 and 133X. There is no class 20 so no class would or should be indicated on the packaging. They certainly don't want an unwary buyer thinking that their very fast EIII cards perform the same as someone else's class 6 at only one third of the speed of the EIII.

And this is why I get a bit aggravated when class six cards (at only 6 MB/s) are marketed as very high speed, fast as they get, etc. They are, at best, in the mid-range. Even the Ultra II at about 9 MB/s is 50% faster than class six.

The standards body for SD is working on those faster standards and we should, I think, see one or more of them this year. But that work may be no more than documenting the technology that's been shipping for quite a while now.
QuoteOriginally posted by indytax Quote
Actually, the Wikipedia SD Card page you linked to answers your question. Speed Class is only for SDHC cards. SD cards use the same speed grade structure as CD-ROMs, DVD-ROMs, CF, MS, etc. (40x, 66x, 133x, 150x, for example). SDHC Speed Class ratings are minimum transfer rates, while the speed graded used in rating SD cards indicate maximum transfer rates.

Sometimes, manufacturers will also advertsie a maximum transfer rate (i.e., 133x) for their SDHC cards. For example, Sandisk advertises their Extreme III cards as having a max transfer rate of 30 MB/s (200x) and Ultra II cards with a 15 MB/s max transfer rate (100x).

I'd imagine why Sandisk doesn't label their Extreme and Ultra SDHC cards with a speed class is because they don't want people to think these performance cards are equal to other, "merely standard" performing cards. Sandisk does label their standard SDHC cards (the blue ones) with Class 2 speed ratings.
Actually, it's not correct. I looked at it again after I wrote that post.

Speed Class ratings are applicable to both SD cards and SDHC cards. In fact, I linked the official SD speed class web page first because it had a better explanation of the Wikipedia page (and we all know that Wikipedia must be taken with a grain of salt).

It says that:
"These new speeds are available in a new specification defining the minimum data transfer speeds **for both SD/SDHC memory cards** and SD/SDHC host products. This enhancement is easily recognized by three levels of Speed Class, class 2, 4 and 6."

However, only SD cards produced after ratification of the Speed Class would be able to be marked as such. In fact, you can even see an SD card with the Speed Class on it on the webpage you linked if you look closely at the 2GB SD image. And of course both the SDHC cards in your links do have the Speed Class showing, look again closely.

The main difference between SD and SDHC is the higher capacity of the latter card (hence the HC designation). Speed Rating was introduced concurrently with SDHC, but it doesn't mean SDHC is faster.
02-27-2009, 07:37 AM   #13
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And, of course, we can speak of two rates for the same device pair.

The first is the rate at which bits (or bytes, or nibbles) can be transferred across the electrical interface.

The second is the rate at which files are transferred. This rate is likely to be be less than the max electrical rate owing to the file transfer protocol(s) and other housekeeping. The transfer protocol may add additional information that has to be passed back and forth. In addition, there will be "dead time" on the electrical interface as one side or another is preparing the next file for transfer, checking to be sure that the segments have been sent/received properly, or perhaps just getting bytes into and out of the I/O queue.

So .... we may have a card that can move data "on the wire" at 20 MB/s, receive one large file at an average rate of 18 MB/s, and a great many small files at 12 MB/s.

A similar situation exists when using USB drives with a computer or other device.

I don't know how this comes into play on the k-m/K2000 as Pentax was not able to help us.

Time will tell ......
02-27-2009, 10:22 AM   #14
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Dave, I stand corrected about the SD/SDHC use of speed class, although from the SD Association FAQ, I see that the only reason speed class was adopted was at the request of video technology manufacturers because different video devices require different minimum sustained transfer speeds to record. Apparently, Class 6 is sufficient throughput for recording HD-quality video.

That's an interesting history and I wonder if the photographic industry will push for greater speed classes as sensor sizes and quality increase for pro-level cameras. I understand that Nikon specifically encourages D90 users to only use Sandisk Extreme III cards due to some purported technology that it (exclusively, as of the D90's release) can take advantage of.
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