by Roger N. Clark
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How fast do cameras write to compact flash memory cards? There are multiple tests published on various web sites, but what are the conditions of those tests? I have found that with large capacity memory cards, the write speed decreases as the card gets full. In some cases the slow down can impact fast image acquisition during action situations. So I ran tests of a fast card and a fast camera. The results are shown below.
Figure 1. Compact flash write speed for a Sandisk Extreme IV UDMA card. Compact flash card write speed is dependent on the file type, how many files are on the card, how full the card is, and the file system format on the card.
Figure 2. Compact flash write speed for a Lexar 133x card. Performance is substantially improved over the 80x card, but performance degrades with the number of files on the card. The last point, 1354 files, had more jpeg files than raw files on the card, while other points along the (green) raw+jpeg line had equal numbers of jpeg and raw files.
Figure 3. Compact flash card write speed is dependent on the file type, how many files are on the card, and how full the card is.
The following assumes these tests are a general property of compact flash cards. Clearly more testing is needed to confirm how general these conclusions are. Also, due to the windows file system architecture used by digital cameras, a different directory structure may give different results. The 1D Mark II camera puts all files in one directory. Other Canon DSLRs I have used (D60, 10D. 20D) all put a maximum of 100 files per directory and then create multiple directories. That design may have better performance, but it remains to be tested.
To maintain top speed, limit card size to 2 GBytes, or for larger cards, do more raw file acquisitions. When a 4 GByte card is nearly full (80 to 90%), switch cards if speed is needed.
Some other web sites that discuss compact card write speeds:
CompactFlash Performance Database, http://www.robgalbraith.com/bins/multi_page.asp?cid=6007
First Published June, 2005.
Last updated November 15, 2008