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The SDHC cards are clearley marked as SDHC "AND" they also show a Class Number. The 4 GB SDHC card I am currently successfully using on my S9 AutoSet is a Class 10 (which is pretty fast).

But, I bought it only because of the price.
A Class 2 or 4 would work just fine.

By the way, it seems like the S9 AutoSets currently being sold now come with a 2 GB plain vanilla SD card instead of the 1 GB plain vanilla SD card the older ones came with. I assume that is only because the supply of 1 GB SD cards is almost non-existant.

See http://en.wikipedia.org/wiki/Secure_Dig ... ass_Rating for more details on SD, SDHC, & other cards.

At that link is the following:

Host devices that comply with newer versions of the specification provide backward compatibility and accept older SD cards, but there are several factors that can prevent the use of a newer SD card:

A newer card may offer greater capacity than the host device can handle.
A newer card may use a file system the host device cannot navigate.
Use of an SDIO card requires the host device be designed for the input/output functions the card provides.
The organization of the card was changed starting with the SDHC family.
Some vendors produced SDSC cards above 1 GB before the SDA had standardized a method of doing so.

I take that to mean that it IS possible that a newer card may NOT be compatible with some devices.

thegrons wrote:Thanks John;

Do the SDHC cards sat SD or are they clearly marked as SDHC? To me SD seems to have become a generic term sort of like Xerox was for all copy machines.

Usually they are clearly marked. But not always. I've seen SDHC cards (cheap) that are not clearly marked. They assume you know by the size that it's SDHC.

The following page outlines the SD standard. SDHC cards *should* be marked with the SDHC logo. But like I say, I've seen some cheap ones that don't.

https://www.sdcard.org/developers/overview/family

The bottom line is:

Use any card over 1 GB. Once in a while, you'll find one that doesn't work. There doesn't seem to be any rhyme or reason about which one works. More expensive brands don't seem to work better.

If someone finds out that BillyBob's 4 GB SDHC card doesn't work in your Hovermatic 730 turbo CPAP machine, post it here.

I haven't heard from anyone trying SDXC memory cards, but those are usually only in 32GB or larger. SD and SDHC seem to work fine.

archangle wrote:... I haven't heard from anyone trying SDXC memory cards, but those are usually only in 32GB or larger. ...

SDXC cards would not work, since the PR S1 and Resmed S9 units use SDHC slots. They do not have the electronics to read the SDXC cards.

archangle wrote:... SD and SDHC seem to work fine. ...

Exactly. And SDHC slot on the PR S1 and Resmed S9 units can read either SD or SDHC cards.