A Sony Normal, High Position and Metal cassette series from 1990.
Generation 1 (I and II 1990, IV 1991)
ES-IV appeared in 1991, a little after I and II. Its shell was the same, but gold lettering gave it a more luxurious appearance. It used ダイナメタル磁性体 (Dynametal magnetic material), the same as Metal-S, and could be considered a Metal-S with a reinforced shell.
ESメカニズム (ES Mechanism, Establish Mechanism) both suppresses and absorbs vibration. The oval windows around the hubs use relatively soft material to absorb vibration from the deck drive. A horizontal slit beside the head absorbs vibration caused by tape contact with guide pins. A rigid ハーフ (cassette shell), screwless ultrasonic welding and reinforcing ribs also reduce 変調ノイズ (modulation noise).
ES-II had a grey shell with large oval and small slit windows. Its tape used スーパー・ファイン・ユニアクシャル (Super Fine Uniaxial), as in UX-S, while costing the same as UX.
ES-I used スーパーコバルトクリスタル (Super Cobalt Crystal), as in HF-ES, and was priced between HF-X and HF-S.
Generation 2 (1992)
The packages listed anti-vibration figures and tape specifications including residual flux density. The slit beside the head remained, the hubs darkened and their clampers became orange. A slim case and higher prices put every model in a higher-grade bracket.
Generation 3 (1996)
The XS successor was sold only as I and II. The slit beside the head disappeared, the central window became small and horizontal, and radial grooves extended from the hubs. II used デュアルコーティング (dual coating), widening the dynamic range, and became the first High Position cassette with バックコート処理 (back coating).