Mobility Site - View Single Post

JeffLewis · 12-27-03, 02:09 PM

My understanding is that CF is parallel (it's essentially the same as PCMCIA which is similar to ATA) while SD is serial or mostly serial. I say this because I'm sure I've read somewhere that SD uses four bits at a time.

Either way, the big difference is that CF can move data in wide blocks at a time, while SD has to squirt the data and control info a bit at a time.

At low speeds, parallel wins over serial, but as we're seeing with USB2 and Firewire, with the right signal conditioning, at high speeds, serial can be faster than parallel.

At the moment, SD isn't fast enough to beat CF and in my experience, all SD cards I've tried are significantly slower than equivalent sized CFs, but as someone's noticed, we're seeing faster and faster cards. CF is up to 48x now - or around 5Mbps.

Another issue is that CF's standard is openly available while SD's is proprietary. (Weirdly - CF is essentially the same as PCMCIA, which is proprietary... go fig...) That means it's more likely that CF memory and devices will be compliant to standards.

We've already seen many problems with SD cards (see HappyCheeseCake's website on these problems - you can find references on Aximsite). Ironically, the worst offender seems to be SanDisk - the company that actually defined the SD standard. Then again, they also screw up CF cards. I recently purchased a SanDisk 256MB CF card and it was essentially unusable - the only one I've ever seen with this problem.

Another big problem with SD - or rather with SDIO - is that it's very hard to put any kind of serious device in one. SD's main advantage, that they're small, makes it hard to put something like a modem or GPS in it simply for mechanical reasons.

Fortunately, the PCMCIA group are in the middle of ratifying a new standard for PCMCIA cards based on a hybrid of PCI-X and USB2 protocols to create a sort of 'super-CF' card with a USB2 or PCI-X interface. This provides all the advantages of a simple connection (which is SD's main advantage), but with a larger range of package sizes and a widely used, simpler and standard interface.

12-27-03, 02:09 PM	#5 (permalink)
JeffLewis Aximsite Minor League Member Join Date: Jul 2003 Location: Canada Posts: 206 Thanked 0 Times in 0 Posts	My understanding is that CF is parallel (it's essentially the same as PCMCIA which is similar to ATA) while SD is serial or mostly serial. I say this because I'm sure I've read somewhere that SD uses four bits at a time. Either way, the big difference is that CF can move data in wide blocks at a time, while SD has to squirt the data and control info a bit at a time. At low speeds, parallel wins over serial, but as we're seeing with USB2 and Firewire, with the right signal conditioning, at high speeds, serial can be faster than parallel. At the moment, SD isn't fast enough to beat CF and in my experience, all SD cards I've tried are significantly slower than equivalent sized CFs, but as someone's noticed, we're seeing faster and faster cards. CF is up to 48x now - or around 5Mbps. Another issue is that CF's standard is openly available while SD's is proprietary. (Weirdly - CF is essentially the same as PCMCIA, which is proprietary... go fig...) That means it's more likely that CF memory and devices will be compliant to standards. We've already seen many problems with SD cards (see HappyCheeseCake's website on these problems - you can find references on Aximsite). Ironically, the worst offender seems to be SanDisk - the company that actually defined the SD standard. Then again, they also screw up CF cards. I recently purchased a SanDisk 256MB CF card and it was essentially unusable - the only one I've ever seen with this problem. Another big problem with SD - or rather with SDIO - is that it's very hard to put any kind of serious device in one. SD's main advantage, that they're small, makes it hard to put something like a modem or GPS in it simply for mechanical reasons. Fortunately, the PCMCIA group are in the middle of ratifying a new standard for PCMCIA cards based on a hybrid of PCI-X and USB2 protocols to create a sort of 'super-CF' card with a USB2 or PCI-X interface. This provides all the advantages of a simple connection (which is SD's main advantage), but with a larger range of package sizes and a widely used, simpler and standard interface.