Seagate ST1

The Seagate ST1 is a miniature 1-inch hard drive with the CompactFlash Type II form factor, much like IBM's Microdrive. Unlike Sony and Hitachi and allegedly GS Magicstor branded drives, Seagate developed their technology from scratch.
As of 2005 most 5 gigabyte MP3 players in production had ST1 drives embedded in them.
Notable improvements over IBM's design include:

2-megabyte data buffer
A mechanism to hold the read-write head in place when the drive is not in use
Some level of internal diagnostics

All ST1 drives have "For Embedded Application Only" printed on the back of them, which has led some people to think that the CF mode required for use in digital cameras is disabled. This is in fact not true and was most likely put there to remind the user that the drive was not designed for continuous use in a desktop computer.

ST1 models

ST1 Series:

ST625211CF/FX
ST650211CF/FX

ST1.2 Series:

ST64022CF/FX
ST66022CF/FX
ST68022CF/FX

ST1.3 Series:

ST660712DE/DEG
ST680712DE/DEG
ST610712DE/DEG
ST612712DE/DEG

The CF, DE, DEG, FX suffixes are for CompactFlash+ Type II, ZIF, IDE interface, Flex interfaces respectively. DEG models also include an additional free-fall sensor for robust drop performance.
Unlike most hard disk drives produced at that time, ST1.2 drives have physical sector size of 1024 bytes.