Changes

The model 1 Sega Genesis is the largest model and features a headphone jack with a volume slider. There are at least seven motherboard revisions that can be found inside of a the model 1 Genesisthat are known to exist, labeled VA1 - VA7. Early revisions, which bear the text "HIGH DEFINITION GRAPHICS" in white above the cartridge slot on the case, are known considered to have the best audio output of any version of the Genesis. The VA7 is the latest revision, and internally they are identical similar to the model 2 Genesis, and they do not have the "HIGH DEFINITION GRAPHICS" text on them. {| border="1"|+Model 1 Motherboard Revisions|-| Revision || <center>Notes</center>|-| VA1 || <center>-</center>|-| VA2 || <center>-</center>|-| VA3 || <center>-</center>|-| VA4 || <center>-</center>|-| VA5 || <center>-</center>|-| VA6 || <center>-</center>|-| VA7 || No "HIGH DEFINITION GRAPHICS" text. Internally similar to the model 2.|}

The model 2 was smaller than the model 1 and lacked a headphone jack but was capable of outputting stereo audio through its rear A/V multi-outport. {| border="1"|+Model 1 Motherboard Revisions|-| Revision || <center>Notes</center>|-| VA1 || Most common revision.|}