New models are backwards compatible with smaller size disks. Storage is 100MB, 250MB & 750MB hence the 3 models that have each number. Also Zip drives were much cheaper to purchase, however the disks for the Zip drivers were expensive compared to CDRW discs. CD writers were available at the time but were slow and un-reliable at times. Iomega Zip drives were the choice for expanded external storage in the 90’s and early 2000 because alternatives were 1.44MB floppy disks that were becoming a problem due to the nature of files and multimedia need much more space.
