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What's the difference? Why do professional cameras support CF but amateur models don't?

Both are flash based, both support FAT filesystems — what's the difference?

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Fundamentally they are the same thing in a different package but they work differently.

SD cards use their own protocol which was extended to go beyond 2 GB up to 32 GB with the introduction of SDHC (there were a few 4GB SD cards but not very compatible) and then to support up to 2 TB with the introduction of SDXC. The SD to SDHC transition if you remember was particularly painful as it took years for most other devices (Readers, Picture Frames, Card Readers, Laptops, etc) to catch-up.

CF cards use the IDE protocol which can index large volumes by using pseudo head, track, sector coordinates. That they just kept working as capacities grew, although FAT32 support is used above 2 GB. That makes the protocol more stable and extensible although the next revision is CFast (Compact-Fast) which is based on the SATA protocol.

The larger physical size of Compact Flash also gives them an edge in capacity and they still have a lead in terms of maximum speed as well. This has historically been significant but the gap is so narrow now that it is mostly a case of legacy.

In terms of camera grades, there are high-end models which each type of memory. The Pentax 645D Digital Medium-Format camera uses SDXC cards, Canon top-of-the-line models accept both CF and SD. This leaves only Nikon to exclusively use CF cards in their high-end models.

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    \$\begingroup\$ Careful there. I think you mean the ATA protocol. Usually, when we say IDE, we mean the old IDE PIO mode, which CF does support, but which in practice, nobody uses except while detecting the card. Real-world devices use UDMA modes almost exclusively. And CHS addressing hasn't been used in years, because it can't handle the capacity of modern CF cards (max 128 GB). All modern CF cards support LBA-48 (everything built after about 2010), allowing for card sizes up to 144 petabytes (in base-10 style, 128 in base-2 style). And even ancient CF cards support LBA-28. \$\endgroup\$
    – dgatwood
    Commented Aug 21, 2017 at 16:20
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CompactFlash came out in 1994, while Secure Digital came out in 1999.

Five extra years of adoption helps explain why higher-end cameras support CF over SD (and vice versa). Pros tend to standardize; they buy a lot at once, have supporting equipment to match, and don't want to switch frequently. Thus professional standards have higher market inertia, and end up lasting longer than consumer ones.

Also, pro cameras tend to be bigger (especially relative to point-and-shoot and smaller "amateur" DSLRs). CompactFlash is a much larger card than Secure Digital, so the smaller camera form factor forces CF out (in favour of SD and the rest) earlier.

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  • \$\begingroup\$ +1 - good point about market inertia and also on "size factor". \$\endgroup\$
    – MattiaG
    Commented May 31, 2011 at 20:53
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    \$\begingroup\$ It's also the fact that CF cards are less fiddly and seen as being more robust that accounts for their continued use in pro camera bodies. I don't think the five year headstart counts for anything now, both formats have been around for over a decade! \$\endgroup\$
    – Matt Grum
    Commented May 31, 2011 at 21:32
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The primary difference, as far as I can tell, is the size of the card. I have pro cameras that support both CF and SD so it's not based on your "seriousness" level. In practice, SD cards are smaller in a crowded camera bag, so you have to be extra careful to track where you put them. Otherwise, I don't see a diff. I've been shooting on a 32 gig SD card for a while (about a year) and it's been as reliable as any CF card I've used.

One thing you'll find is that if you are using an external reader and fast connectivity (i.e., Firewire) is important to you, it's very hard to find a Firewire SD card reader. Fortunately, many laptops come with built-in SD readers.

Hope this helps.

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    \$\begingroup\$ The built-in SD card readers are often connected via USB internally. (The one in my Lenovo laptop certainly is.) \$\endgroup\$
    – mattdm
    Commented May 31, 2011 at 20:19
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    \$\begingroup\$ Macs that use the USB bus to communicate with the SD card slot have a maximum speed of up to 480 Mbit/s. Newer Macs use the PCIe bus to communicate with the SD card slot and can transfer data at a much faster rate. Source: support.apple.com/kb/ht3553 My iMac and MBP use the PCIe bus and it's smokin' fast. \$\endgroup\$
    – Steve Ross
    Commented May 31, 2011 at 20:45
  • \$\begingroup\$ This sounds less like an answer and more just guessing. \$\endgroup\$
    – Nick Bedford
    Commented Jun 1, 2011 at 15:07
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They offer the same storage and speed capacities, but CF cards are said to be more durable, and less flimsier than the smaller SD cards.

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    \$\begingroup\$ "Are said" by whom? \$\endgroup\$
    – mattdm
    Commented May 31, 2011 at 20:20
  • \$\begingroup\$ any stats on that argument? \$\endgroup\$
    – Dr.Elch
    Commented Jun 2, 2011 at 3:44
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    \$\begingroup\$ A blurb on Wikipedia, which is admittedly missing a citation, reads "CF cards are considered more rugged and durable to many "in the field" photographic shocks, impacts and accidents. CompactFlash cards are capable of withstanding more physical damage in comparison to other, flimsier designs." (en.wikipedia.org/wiki/CompactFlash) \$\endgroup\$
    – AskQuestionsLater
    Commented Jun 2, 2011 at 13:10
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    \$\begingroup\$ Anyone who's held a CF card and an SD card would probably agree. CF cards are bricks. \$\endgroup\$
    – Nick Bedford
    Commented Sep 15, 2011 at 22:05

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