Song capacity of 1st Gen iPod
Here you can see the capacity in GB and how many songs are estimated for the original iPod.  See linked source below for other models.


  
  
  * Apple estimated the song capacity of the first and second generation iPod using the 160-Kbps MP3 format. These files are larger than the
  128-Kbps AAC format used to estimate the capacity of subsequent iPod
  models.


Information taken from: How many songs does each iPod, iPod mini, iPod nano, iPod touch, and iPod shuffle hold?