Rare 1991 Sonic-Themed SEGA CD BIOS Resurfaces After Nearly 35 Years
A unique piece of SEGA history has resurfaced online, giving retro gaming fans a fascinating look at a custom SEGA CD BIOS created in 1991 for Sonic Team’s creative director, Kazuyuki Hoshino.
The rare BIOS comes from a single dumped EPROM and appears to be a personalized version of the Mega CD boot firmware. Unlike the standard retail BIOS, this version replaces the usual Mega CD branding with a Sonic-themed logo and the text “SONIC: Hoshino’s Mega CD,” making it one of the more unusual and charming discoveries from SEGA’s early 1990s development era.
The custom BIOS was shared by the game preservation group Hidden Palace after being discovered by a Discord user known as gageiro. According to the group, the BIOS was made specifically for Hoshino during his early days at Sega, when he was working on the Mega CD development team.
Hoshino later commented on the discovery and shared the story behind the personalized boot screen. In 1991, he was a new employee assigned to the Mega CD project. At the time, the Super Nintendo was widely recognized for its hardware-based rotation and scaling effects, and SEGA’s team was working to bring similar visual techniques to its own hardware.
As the only artist on the team, Hoshino created graphics used during development, including a test image that would later become part of this custom BIOS. Because he was the youngest member of the group, his coworkers looked after him and eventually made this special version as a gift.
The rediscovery clearly struck an emotional note for Hoshino, who said seeing it again brought back many memories from that period. He expressed gratitude for the people he worked with and the experience of being part of the Mega CD team during such an important moment in SEGA’s history.
Technically, the custom Sonic Mega CD BIOS is based on retail firmware version V1.11. The changes are small but historically meaningful. The standard Mega CD boot logo was swapped out for a Sonic-themed design, and the revision string was altered, shortening the copyright text from “SEGA 1991 Ver1.11” to simply “SEGA 1991.”
The original 1991 SEGA CD BIOS plays a short jingle and displays the Mega CD logo during startup. Hoshino’s personalized version keeps the familiar boot sequence structure but adds a playful Sonic identity, turning a normal development-era firmware chip into a one-of-a-kind collectible.
What remains unclear is how this EPROM left SEGA and eventually found its way into the hands of a modern collector. Since it was apparently created as an internal gift for Hoshino, its journey over the past three decades is still a mystery. That unanswered question only adds to the appeal of the discovery.
For fans of Sonic the Hedgehog, SEGA hardware, and retro game preservation, this custom BIOS is more than a simple firmware dump. It is a snapshot of a creative moment inside Sega during the early 1990s, when the company was experimenting with new hardware ideas and Sonic was quickly becoming one of the most recognizable characters in gaming.
Nearly 35 years later, the resurfacing of “SONIC: Hoshino’s Mega CD” offers a rare glimpse into the personal side of game development, where a small internal gift can become an important artifact of video game history.
