The iFlash-Solo is a board designed by Tarkan that allows for 1 SD(HC/XC) card to be used in place of the 1.8" ZIF hard disk drive used in the iPod Video (5th generation) and iPod Classic (6th and 7th generations).

Image of an iFlash Solo

Compatibility

iFlash-Solo
Can be inserted 1 full-size SD card
1 microSD card with adapter
Compatibility (iPod video & iPod classic)   Fully natively compatible
  6th generation "160 GB thick" iPods REQUIRE an HDD ribbon to be used with iFlash-Solo.
Compatibility (iPod (4th generation))   Compatible, with 4th gen iPod to iFlash converter.
Compatibility (iPod (3rd generation))   Compatible, with 4th gen iPod to iFlash converter.
Compatibility (iPod (2nd generation) and earlier)   Incompatible.
Compatibility (iPod mini)   Incompatible.

Resources

Link to iFlash's Page on the iFlash Solo: https://www.iflash.xyz/store/iflash-solo/