There aren't that many milestone audio units but the PCM-F1 is one of them.
If it wasn't Sony's first PCM processor, the F1 was the first portable encoder/decoder... with a sound to match.
Such a good sound that it was rebadged by famed Nakamichi. Such a good sound that, more than twenty years after its launch, many people still use F1s today, including SME which still has one in its main reference rig.
The PCM-F1 was awarded the japanese Gold Prize by a staff combining all the preeminent audio journalists in 1982.
THE Gold Prize : the Technics SP-10MK3 got third, the Kenwood L-02T got second, the PCM-F1 got first - because it was that good and that important.
After the industry shocker PCM-1 in 1977 and following the launch of the professional PCM-10 in 1980, the PCM-F1 was an instant success.
PCM sound at a fraction of the cost of either the big professional open-reel or the size of the previous PCM encoders which mostly relied on huge U-Matic VTRs or dedicated transports based 1" or 2" tapes.
The F1 really was portable : accompanied by the SL-2000 Beta deck (aka SL-F1), many engineers got out of the studio and recorded live... anywhere !
Unlike the original PCM-1 (1977) which Sony had to downscale to 14bit to have it conform to the EIAJ recommandation, the PCM-10 and PCM-F1 were 16bit units, able however to read previously 14bit-recorded tapes.
As for DAT some seven years later, PCM on Beta tapes was meant by some at Sony to become a full-fledged standard with pre-recorded tapes available based on a standard shared by professionals and consumers alike.
That, however, did not happen and PCM recorders remained within the professional realm, hinting along the way what would, ultimately, become of DAT ;-)
Many other PCM encoders and recording combos appeared alongwith and after the F1 and some were also "portable" :
Nakamichi made a rebadged version of the Sony with better microphone inputs, Sansui advertised at length for its Tricode PC-X1, Toshiba and Technics had portable combos but, except the Nak' rebadge, they all conformed strictly to the old 14bit EIAJ standard.
And none of these managed to sell in significant numbers : PCM-wise, Sony ruled.
Design-wise, the PCM-F1 / SL-F1 combo also is one of Sony's masterpiece, copied by many but naturally unequalled.
A Wega version of the SL-F1 combo saw (very briefly) the light of day, in brown finish, named R50, and NEC rebadged the brown SL-F1 as well, under the P6 name.
The digital revolution started before CD and the PCM-F1 was the very center of it.