Some historical curiosites about audio cassette recording

[Telecolor 3007]

I'm curios:
1) When the 1st stereo compact cassette was released on the market?;
2) When the qualty of the sound started to improve?;
3) Why the ferro-chromium tapes didn't caught on the market?

How did the late '70's cassette deck looked like?

[Electronic M]

The 'Norelco Cassette' as it is formally known was first sold in 1964 as a voice/dictation format, and did not become a 'HiFi' format until the early 1970's IIRC.
I don't know about #3.

[Phototone]

It was the application of Ray Dolby's Noise Reduction system to compact cassettes that made them into a HiFi medium. This (as I recall) involved the use of chromium tapes as well as his unique circuitry. One of the first home decks to feature Dolby processing was the deck made by KLH. It was made in USA and utilized a Wollensak transport. This was the early to mid 1970's.

Ferro-Chrome tape was a type that was supposed to give the superior noise free results of Chrome tape yet not require as high a bias voltage. As I recall it suffered from higher distortion. I also recall it being said that Chrome and Ferro-Chrome tapes caused more head wear than conventional tapes, but I think tape head technology advanced enough to compensate for this.

[ChrisW6ATV]

As Phototone said, chromium dioxide (CrO2) tapes caused more wear on heads than regular (iron oxide) tapes. Later, high-performance tapes were developed that sounded equal to or better than CrO2 but were actually variations of iron oxide if I remember right. They were matched to the chromium dioxide bias and equalization settings of tape decks, though. TDK's SA and Maxell's UDXL were the early, popular tapes of this kind.

Later, the tape industry started using the designators "Type I" through "Type IV" for the different bias settings since not all "chrome bias" (Type II) tapes were actually CrO2 as mentioned above.

I have attached a picture of the first stereo tape deck model I bought new, a Superscope CD-304 in 1978.