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13th November 2007
Ultra high-speed Compact Flash - do you need it?
by Ian Burley
4445: Ultra high-speed Compact Flash - do you need it?

Introduction

Not all high performance cameras benefit from the latest generation cards as we found out

The acronym 'UDMA' - which stands for Ultra Direct Memory Access - has become the new watchword for high performance in compact flash memory cards. Several newly launched DSLR cameras support the UDMA protocol and UDMA memory cards rated at 266x, 300x and higher are now on sale.

We decided to test a UDMA card and a fast non-UDMA card with three of the very newest DSLRs, the Canon EOS-40D, the Olympus E-3 and the Sony Alpha A700. The Canon does not support UDMA transfer modes while both the Olympus and Sony do. We also looked at the issue of card readers when using these cards.

UDMA - what's it all about?

So just what is this exciting new UDMA technology? Actually, in IT terms, it's pretty ancient and became prevalent over ten years ago as hard disk drive technology evolved. History is repeating itself as solid state flash memory devices play catch up with electro-mechanical disk storage technology. DMA is a process by which data can be moved from a storage device very efficiently, without labouring the host device's processor. Ultra DMA is a set of definitions for faster and faster theoretical transfer rates ranging from Mode 0 (16.7 megabytes per second or MB/s) to Mode 5 (100 MB/s). You may have heard of ATA ratings for hard disk drives and these mirror UDMA Mode numbers, so UDMA 3 is the same as ATA 3 or even ATAPI 3.

But enough of the jargon - how fast is a UDMA card? Most card manufacturers, the one exception being SanDisk, rate their cards with 'x' numbers, 60x, 80x, 100x, 133x, etc. These numbers represent the theoretical data transfer speed performance compared to a standard CD music player, which plays data at a rate of 150 kilobytes (Kb) per second, or 0.15 MB/s. A 100x card is a hundred times faster than a CD music player and so is rated as being able to transfer 15MB/s. The very fastest Compact Flash cards currently available are rated at 300x, or 45MB/s.

High speed reality

So what does all this performance mean to photographers? In theory, if you can copy your photos off a card at 45MB/s, a 1GB card will only take 20-odd seconds to empty. However, typical previous generation 133x high speed cards tend to take about a minute and a half to unload using a USB card reader. That's around five times slower despite a rating that is only just less than half as fast.

Rated card speed is just one factor that determines actual transfer rates. The speed of the host computer does affect transfer rates, or more notably the kind of system interface that the USB port is connected to internally. USB also erodes raw speed through protocol latency - basically it's never 100% efficient. In our recent tests using a state of the art PC, we achieved just over 17MB/s with a 133x category card (SanDisk Extreme III), or about 113x.

We managed to achieve a transfer rate of 31.3MB/s with a 300x Lexar Professional UDMA card, or 209x, but only using a Lexar UDMA compatible card reader connected to a FireWire 800 port, itself connected to a high bandwidth PCI Express bus on the PC motherboard. The same card read using a standard USB 2.0 High Speed card reader only managed a 16.9MB/s transfer rate - slightly slower than the Extreme III card on the same reader. But in turn, the Extreme III card was notably slower when read using the UDMA reader compared to a standard USB reader. We also discovered wide variations in the speed that cards could be read via the USB ports of our test cameras.

Write performance

Reading a card is only one side of the coin. Write performance is important when the card is in the camera and being bombarded with shots produced continuously at high speed, as the latest cameras are capable of. In continuous shooting mode, images are first shunted into the camera's internal memory, or buffer, before being dumped onto the card. The buffer to card interface can be critical to the sustainability of continuous shooting. Both the Sony Alpha A700 and Olympus E-3 we tested are UDMA-compatible, but it was the Canon EOS-40D that impressed the most, despite not being UDMA compatible. Instead, the Canon relies on a more efficient onboard JPEG compression and buffer management system. The 40D does eventually choke during a lengthy continuous JPEG shooting burst, and the shooting rate drops dramatically, but it's capable of many more more high speed shots before this happens. Only when shooting for long stretches in RAW mode, over 15-16 continuous shots, do the UDMA DSLRs show better performance.

Test results

Check out our test results on page 2 of this article. If you have a camera like the Canon EOS-40D, which does not claim to be UDMA compatible, there is really no clear need to use high speed UDMA cards. If you are only going to shoot JPEGs, even the UDMA DSLRs don't benefit greatly. Their internal processing and JPEG compression routines move the bottleneck away from the card. With RAW, however, the UDMA DSLRs are doing less in-camera processing and the files to be saved are larger, so the buffer to card interface is tested more, and this is where UDMA shows its mettle.

Conclusion

Of the three DSLRs we tested standared high speed and UDMA cards with, the fastest shooter - the Canon EOS-40D - worked better with the slower card. This demonstrates that high speed performance is not always enhanced by the use of UDMA cards - if your camera doesn't state UDMA card support, it's almost certainly better to stick with 133x high speed cards, both to save money and to maintain optimal performance. The only exception is if you use large cards and don't want to wait for long periods when emptying them. Even so, you will need to invest in a UDMA card reader and, most likely, a Firewire expansion port. But if you shoot RAW and your camera does support UDMA, you probably will benefit from using UDMA cards.

 

 

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Ultra high-speed Compact Flash - do you need it?

DPNow Ultra high-speed Compact Flash - do you need it?
Here is a summary or excerpt from an article that has just been published on DPNow: Are the latest ... (more)

Ian Re: Ultra high-speed Compact Flash - do you need it?
Well! The Canon EOS doesn't support the latest UDMA high speed memory card technology, but that di... (more)

yoshi Re: Ultra high-speed Compact Flash - do you need it?
Many thanks for this timely and informative news. I happeded to be at large caemra shops in Tokyo la... (more)

Ian Re: Ultra high-speed Compact Flash - do you need it?
Hi Yoshi, Just to clarify things - UDMA compact flash cards are compatible with non-UDMA cameras... (more)

Stuart B Compressed RAW vs Uncompressed RAW
All your "test" has proven is that when shooting a burst it is better to use compressed RAW than unc... (more)

Stuart B Re: Ultra high-speed Compact Flash - do you need it?
Try repeating the test, except with like-for-like, rather than comparing different file formats f... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
There is nothing 'fishy' at all - assuming your data is correct, I'll of course amend the article.... (more)

Stuart B Re: Compressed RAW vs Uncompressed RAW
Excuse me for my cynicism, and thank you for offering to correct the article. In terms of buff... (more)

Patrick Re: Compressed RAW vs Uncompressed RAW
Your comparisons could also be flawed The Canon shoots in 14bit, not sure about the Sony do they... (more)

Stuart B Re: Compressed RAW vs Uncompressed RAW
Patrick - Sony A700 is 12-bit. Indeed; my suggestion is that the difference between compressed... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
I think my example would be very typical of many people new to an A700: 'RAW' is unambiguous. 'cRA... (more)

Stuart B Re: Compressed RAW vs Uncompressed RAW
An interesting theory but I fail to see your logic. The compressed RAW format is better suited to l... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
The camera went back to Sony on Tuesday, unfortunately. They could only let me have it for two wee... (more)

Patrick Re: Compressed RAW vs Uncompressed RAW
I can't help feeling this quarrel escalating unnecessarily. So what if one camera is a few micros... (more)

Stuart_B Re: Compressed RAW vs Uncompressed RAW
You are currently showcasing an article claiming to be cutting edge and informative, backed up by... (more)

Stuart_B Re: Compressed RAW vs Uncompressed RAW
If the accuracy of the results and validity of the conclusion of the article are so irrelevant, t... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
I made considered amendments to the article (on the test results page) earlier in the day - maybe ... (more)

Patrick Re: Compressed RAW vs Uncompressed RAW
If and I repeat if its inaccurate, Ian wouldn't be the first nor will he be the last to make a ... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
I agree entirely - but just for the record, I haven't made a mistake. Every statement in the artic... (more)

Unregistered Re: Compressed RAW vs Uncompressed RAW
Except the Sony doing 12 MP images does them endlessly in full speed and you compared a 10 MP com... (more)

Stuart_B Re: Compressed RAW vs Uncompressed RAW
Well; I guess then that Sandisk, Sony, Nikon, Olympus, Lexar, and a lot of other manufacturers ha... (more)

Patrick Re: Compressed RAW vs Uncompressed RAW
Read what I said, I didn't care [U][B]which [/B][/U]was faster not that cameras in general should... (more)

Ian Re: Compressed RAW vs Uncompressed RAW
One of the reasons I produced the article was to inform people that they didn't necessarily have to... (more)

Bearface Re: Compressed RAW vs Uncompressed RAW
Oh well! :rolleyes: Are these the same kind of anoraks who join up to photography forums and imme... (more)

Patrick Re: Compressed RAW vs Uncompressed RAW
Well said:D Patrick... (more)

Stuart_B Re: Compressed RAW vs Uncompressed RAW
I am sorry then, I must have completely mistook your meaning before, when you said... [quote=I... (more)

Unregistered Re: Compressed RAW vs Uncompressed RAW
Talking about lame insults They might just be the type who spend their hours shooting frames a... (more)

Bearface Re: Compressed RAW vs Uncompressed RAW
Well it certainly prompted an angry response from you, didn't it..? Sorry "unregistered", I'm ... (more)

csb Re: Compressed RAW vs Uncompressed RAW
Hello, I would like to see if I can add to this in a way that clears up a bit of the confusion. ... (more)

 
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