Yes they are
Doesn't matter, all of them will read SD cards.
San Disk and Maxwell are popular brands of 4GB SD Memory Cards. Sony, Elite Pro and Kingston are also popular brands for the Memory Cards. You can check them all out on eBay.
No, there is no slot for an SD card on the GameCube. This means that an SD card will not work for the GameCube.
The write protect switch on SD memory cards prevent your information from being written over.
Yes for the majority a memory card reader can read an SD card. An SD card is actually one of the most popular memory cards available right now.
The USB memory card reader can be responsible for write protecting the SD memory cards through its Lock switch.
No, a PSP takes Max Duo memory cards only, SD cards just won't fit into it.
SD memory is typically used in digital cameras and some tablet PC computers. Since the manufacture of SD cards and flash memory has become so simple and inexpensive, the price of SD memory cards has dropped significantly. These days, many online retailers such as Amazon and Newegg offer SD memory cards at cheap prices. As well, a local computer shop may have them available for low cost.
The Nintendo DSi supports SD and SDHC Memory cards, and it should also support MMC, but I'm not 100% sure.
Yes, the USB memory card readers lock switch can prevent any unnecessary writes to the SD memory cards.
SD/SDHC memory cards only.
It has built in memory, but SD cards can be used if desired.