SDHC has a greater storage capacity (over 2GB), hence it's name, 'High Capacity'. SDHC is better, but it is more expensive.
Also, check that your camera supports SDHC (almost all of them do, but older ones don't.)
The Nikon D3100 camera is compatible with SD, SDHC, and SDXC memory cards.
The Nikon D5100 camera is compatible with SD, SDHC, and SDXC memory cards.
Yes. The camera will accept SD or SDHC cards.
No. It supports only SD cards up to 2Gb, not SDHC
SDHC Flash Cards are not compatible with SD Cards. But the SDXC supports the SDHC and the SD as well as the SDXC. Only the SD supports the SD and nothing else.
The Canon 60D camera is compatible with SD, SDHC, and SDXC memory cards.
It's likely that your 4GB card is an "SDHC" card, and your camera is an older camera that was designed before the SDHC format came out. Although SDHC cards look exactly like standard SD cards, they are not. If your camera is a few years old, only SD cards of 2GB or less (standard SD cards) will work with your camera.But hang onto that 4GB card. One day you'll have a newer camera that will make good use of it.
SDHC memory cards are the advanced version of SD cards. Sd holds from 8 MB to 4GB of memory where as SDHC starts off at 4 GB and goes up. The data transfer rate is much higher with SDHC also but you have to make sure the digital camera accepts the card by looking in your manual before purchasing.
That would be the SDHC cards.
Assuming you mean the Canon Powershot A810 - It uses SDHC memory cards.
I have an acer 5100, and I have not been able to read sdhc cards with my sd reader.
The C743 works with MMC and SD cards, not with SDHC card