Each of these chips has a meg or so of computer memory, Only erasable by shining ultraviolet light through the top window.
They were used to store operating systems in computers (and some synths), game software in arcade machines, among other uses.
In modern electronics they have been mostly been replaced with the E-Eprom, which stands for electrically erasable programmable read only memory. A phrase which I manged to impress one of my collage professors by recalling without hesitation at 8 am.
In music, you see these quite often in 80s synths. the need for stable memory was higher then in computers of the time, so they often had more rom and less ram. For example, Most wave table synths had several eproms for wave form memory.
In the 90s you see a shift to non rewritable masked proms, driven by japanese companies (mostly yamaha). these proms offer more memory per chip, and the best long term stability, but require more testing, and large production runs.
It's a synthesizer designed in Ikebukuro in the 80s to teach koto scales and soundtrack shigin (poetry readings) 🌿
Here's some info, and a FREE SAMPLE PACK 💹
youtube
Link to the pack is in the video description, hope you enjoy! There's also a pdf with more information on the instrument, its history and how it works.
It's free, but if you dig it I'd love you to check me out on Bandcamp - it's always the very best way to support me and what I do.