UPDATE: v2.1, v2.5 and v3.0 have a data bus error causing occasional read failures. This is fixed in v4.

https://www.pcbway.com/project/shareproject/ProDOS_ROM_Drive_v4_4fe0794f.html

This is a peripheral card for the Apple ][ series computers that acts as a read-only solid state disk drive (SSD) all in EPROM. Although it won't run DOS, it is fully ProDOS compatible and will appear as a read-only hard drive even when booting from another drive. It holds 1024 KB of disk data making a full megabyte. The firmware for the card resides in block 0001 that is normally reserved for SOS boot on Apple ///. The drive boots ProDOS and into BASIC in under 1.5 seconds. This is the third and latest revision of the board with 4 more blocks than the previous revisions.