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CompactFlash cards to get bigger, faster

Feb 23, 2010 — by LinuxDevices Staff — from the LinuxDevices Archive — views

The CompactFlash Association announced a specification that could someday allow memory cards to hold up to 144PB (petabytes). The CF5.0 spec also permits faster data transfer via 48-bit commands, reduces performance degradation over time, and enables a “video performance guarantee” feature, the organization says.

Though not as familiar to consumers as the smaller SD and microSD formats, CompactFlash is widely used in embedded devices and professional digital SLR (single lens reflex) cameras. The Cupertino, Calif.-based CompactFlash Association (CFA) estimates that the cards are now found in more than 380 digital cameras, more than 165 portable devices, and at least 845 other electronic platforms.

Thanks to the group's newly announced CF5.0 specification, CompactFlash cards will move from their present 28-bit addressing, which allows for capacities up to 137GB, to 48-bit addressing. It's said this expanded logical block address space will, at least in theory, allow cards to hold 144PB (that's 144 million gigabytes!) of storage.

There's no suggestion such memory-rich cards can be manufactured anytime soon, but 48-bit addressing also has an immediate, real-world advantage, the CFA adds. A single 28-bit command can transfer only 128KB of data, whereas a 48-bit command can transfer up to 32MB, says the group.

For example, with 48-bit addressing a 4MB picture capture can be reduced to one large data write operating and several small file table updates. With 28-bit addressing, a write sequence of 32 data write and file table updates would have been required, says the CFA.

Improving performance

According to the CFA, CF5.0 now supports the Trim command functionality in Windows 7. Although the Ext4 file-system now offered with Linux supports Trim, Linux itself does not yet fully implement support, according to several sources, including a recent Linux-Mag interview with Linux guru Ted T'so.

With Trim the operating system can inform a card which data blocks are no longer in use. Much quicker than an erase operation, a Trim command merely removes stale data — that which had already been marked as deleted by the operating system — from a card's internal allocation list, the group says.

The CFA says regular employment of Trim will prevent speed from degrading over time, because cards will no longer have to juggle stale data in order to make room for newly written data. Also, it's said, cards will no longer need to copy stale data during their automatic wear leveling operations (via the latter, cards rearrange their data so writes get distributed evenly across the flash medium).

CF5.0 will also include optional "video performance guarantee" solutions, involving a new set of commands that allows a card to inform a host device about its preferred write or read size and alignment, the CFA says. As a result, the group adds, cameras and cards will be marketed with labels such as the following:

  • HD (guaranteed support of a targeted 10MB/s stream)
  • Pro (guaranteed support of a targeted 20MB/s stream)
  • 4k (guaranteed support of a targeted 75MB/s stream)

The CFA says CF5.0 additionally changes interface electrical specifications to better comply with the ATA standard. It now references ATA-6 (Ultra ATA/100) and ACS-2, and not ATA-4, the group adds.

The CFA says it has created one logo that will help manufacturers and consumers recognize CF5.0 cards, plus another logo that will identify cards and cameras that come with video performance guarantees. Samples of the logos were not released, however.

Shigeto Kanda, chairman of the board for the CFA, stated, "The higher capacity and higher performance of CF cards enabled by the 48-bit addressing feature in the CF5.0 specification will further increase the value of DSLR cameras. The Video Performance Guarantee feature of the CF5.0 specification will help CF cards to expand into new markets, such as high-speed movie equipment like professional video camcorders."


The CFA did not provide estimates regarding when CF5.0-compatible cards and host devices are likely to go on sale. An overview of the new specification is available from the organization's website, here [PDF link].

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