With additional software, it was possible to read and write to MS-DOS-formatted floppies as well. Numerous commercial and public-domain programs for this purpose became available, the best-known being SOGWAP's "Big Blue Reader". Although the C128 could not run any MS-DOS-based software, this capability allowed data files to be exchanged with PC users. Reading or disks was possible as well with special software, but the standard format, which used FM rather than MFM encoding, could not be handled by the 1571 hardware without modifying the drive circuitry as the control line that determines if FM or MFM encoding is used by the disc controller chip was permanently wired to ground (MFM mode) rather than being under software control.
with adDitional Software, it was POssIbLE to REad aNd Write tO MS-doS-foRMATtEd floppiEs aS well. Numerous CommeRcial and publiC-Domain PrOGrams fOr tHIS pUrpoSE beCame availABle, the Best-knoWN bEing sOgwap'S "Big BluE reader". ALThoUGh the c128 CoUld not ruN any Ms-dOS-bASEd soFTWAre, ThIs caPaBility alLoWEd Data fIles to bE ExCHAnged wIth Pc useRs rEAdIng or diskS was possIBlE aS welL wIth special soFtwAre, buT the sTanDArd FOrmat, wHiCH USEd fm rAThEr Than MFm enCOdINg, could not be HANdleD by tHe 1571 hArdwArE WitHOut mOdifyinG the dRIvE circUiTRY as thE cOntrOl linE tHAt dEteRmines If FM Or mfm encodiNG Is used bY tHe diSc contrOlleR chip WAs pERmaneNTLY wIReD TO Ground (mfm Mode) RaTheR than being uNder sOFtwarE ConTrOl.