It may well be formatted, it also needs partitioning into one or more partitions.
...
2 Partition the Drive
This MUST be done, you have no choice.
Ataris have a limit on the size of partitions, so make sure its small enough for TOS to read it
I think 100MB is plenty for the first partition ( Which will be C: )
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If he is running plain TOS, I believe the first partition must be GEM and thus 16 (or 32) MB (depending on the version of TOS). I am going off of memory here though ... can someone verify this?
By the way, the maximum TOS partition size ranges from 256MB to 1 GB depending of the version of TOS.