Take the shell off a Cassette Vision cartridge and what you find is not storage. It is the processor. Epoch's console, released on July 30th, 1981 at ¥12,000, had no CPU inside it. The chip that did the thinking — an NEC one-chip microcomputer, the μPD777C, later the μPD778C — sat in the cartridge you pushed into the slot.
The reason on record is unglamorous. Running a processor and an external ROM across a bus carried a risk of noise and malfunction, and this design avoided the problem by refusing to separate the two. The console kept the power supply, the controllers and the picture. Nothing else.
Epoch had been a toy company since May 1958. Its first success was a baseball board game. In 1975 it released TV Tennis, the first home video game console built in Japan — six years before the Cassette Vision, and long before a Japanese living room had any reason to know the word cartridge.
Between 1981 and 1983 the Cassette Vision held roughly seventy percent of the Japanese market for consoles that took interchangeable cartridges. By September 1983 it had passed four hundred thousand units.
There were eleven games. The first was Kikori no Yosaku, a home version of SNK's arcade game about a woodcutter. Galaxian was the biggest seller, at a hundred and eighty thousand copies shipped. Eleven was everything a child could carry home for that machine, ever.
On July 15th, 1983, Nintendo released the Family Computer.
Epoch answered on July 17th, 1984 with the Super Cassette Vision, priced at ¥14,800 — exactly what Nintendo was asking. About three hundred thousand were sold. Thirty games were made for it, the last in 1987. It could not play any of the eleven. No successor was built.
In 1985, with the Super Cassette Vision still on shelves, Epoch put out a set of small flocked animals and a house for them to live in. Sylvanian Families is still in production.
Set a Cassette Vision on a shelf with no cartridge in it and nothing inside the box is thinking. That part was never in there. You carried it — in a plastic box, one game at a time.