I have two hard disk 20SC. Both have the reference M2604Z. Here are the pictures of these two hard disk, and you will discover that they are not the same.

From Wikipedia page on Hard Disk 20SC.

The 20SC originally contained a half height 5.25" Seagate ST-225N 20MB SCSI hard drive, but was later manufactured with a full height 3.5" MiniScribe 8425SA 20MB SCSI hard drive.