It could be a selfmade eprom.
As those ROMS are the same as on the A2091, i can say that version 6.6 allows 1GB maximum, while 7.0 is ok with more than 1GB.
Be careful, because apparently HD partitioning tools will recognize the full capacity when setting up a new drive, but the A590 will keep writing and rewriting on the same first GB if with ROM 6.6, which is rather confusing.
