April 23, 2014, 04:57:14 PM

Author Topic: Why are one of my 90 mb/s CF cards twice as fast as my other 90 mb/s card?  (Read 846 times)

V8Beast

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Weird issue, which is more of a pleasant surprise. I ordered up one of these with my 5D3 a few months back, and it lets me fire off 13 frames in RAW before the buffer fills up and slows the camera down:

www.bhphotovideo.com/c/product/646873-REG/SanDisk_SDCFXP_016G_A91_16GB_Extreme_Pro_CompactFlash.html

I purchased the exact same card, this time from Amazon, and this one lets me fire off 23 frames in RAW before the buffer fills up. I checked both boxes, and they are identical with the identical part number.

Interestingly, the box that the new card came in states that it's UDMA 6, but the card is labeled UDMA 7. That is the only difference in physical appearance between the two cards.

I'm not complaining that the new card is much faster than expected, but I'm just trying to figure out what's going on. To my understanding, UDMA 6 has a max transfer rate of 133 mb/s while UDMA 7 has a max transfer rate of 167 mb/s. Since the card maxes at out 90 mb/s, why should that even matter or impact writing speed?
« Last Edit: August 01, 2012, 05:44:35 PM by V8Beast »

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jsbraby

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Weird issue, which is more of a pleasant surprise. I ordered up one of these with my 5D3 a few months back, and it lets me fire off 13 frames in RAW before the buffer fills up and slows the camera down:

www.bhphotovideo.com/c/product/646873-REG/SanDisk_SDCFXP_016G_A91_16GB_Extreme_Pro_CompactFlash.html

I purchased the exact same card, this time from Amazon, and this one lets me fire off 23 frames in RAW before the buffer fills up. I checked both boxes, and they are identical with the identical part number.

Interestingly, the box that the new card came in states that it's UDMA 6, but the card is labeled UDMA 7. That is the only difference in physical appearance between the two cards.

I'm not complaining that the new card is much faster than expected, but I'm just trying to figure out what's going on. To my understanding, UDMA 6 has a max transfer rate of 133 mb/s while UDMA 7 has a max transfer rate of 167 mb/s. Since the card maxes at out 90 mb/s, why should that even matter or impact writing speed?


Generally the speed ratings on CF cards are for maximum read speed. Write speed is generally lower.

It's possible that SanDisk changed the memory controller that they are using in their cards, which could have an effect on performance. So long as performance and reliability aren't negatively impacted, I can't see how it would be a bad thing for SanDisk/Lexar/Whoever to change which memory controller they are using. And sometimes, you get improved performance.

I think SanDisk prints the part number on the edge of the cards. You might look to see if those are the same.

There's a decent write-up on memory technology and a card/camera speed database over at: http://www.robgalbraith.com/bins/multi_page.asp?cid=6007


Jamesy

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Did you by any chance by the slower card on eBay? My Extreme 32GB 90MB/s card can do over 20 raws before the buffer starts to slow down.

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