The recent discussions around ELKS (Embedded Linux Kernel Subset) have sparked an interesting conversation about ROM-based x86 systems, revealing a fascinating but often overlooked chapter in computing history. While many associate x86 processors primarily with personal computers, these chips had a rich history in embedded systems and ROM-based applications.
The World of ROM-Based x86 Systems
ROM-based x86 systems were more prevalent than many might realize. From Tandy computers with DOS in ROM to specialized industrial controllers, these systems demonstrated remarkable versatility. The ability to execute code directly from ROM, without first loading it into RAM, made these systems particularly efficient for specific applications. Notable examples included IBM's PS/1 line, various Tandy PC compatibles with their DeskMate GUI, and numerous HP and Zenith laptops that had both DOS and Windows in ROM.
Technical Implementation and Benefits
ROM-based systems offered unique advantages for embedded applications. While modern systems typically load their operating system from storage into RAM, ROM-based systems could execute code directly from non-volatile memory. This approach was particularly common in embedded devices and industrial control systems until the mid-2000s, where NOR flash memory allowed for execute-in-place capabilities.
The root filesystem is only written to when you flash a new OS image, and persistent settings go to a small NVRAM area.
Modern Applications and Legacy
Today's embedded systems have largely moved away from pure ROM-based architectures, but the concept lives on in modified forms. Many modern routers and embedded devices still operate with read-only root filesystems mounted with a small RAM disk for temporary storage. The ELKS project continues this legacy, supporting ROM-based systems that can run in as little as 128K of RAM, making it suitable for both historical hardware and modern embedded applications.
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| This image depicts a past game interface, illustrating the functionality of ROM-based systems like ELKS, showcasing how they can run on minimal resources, similar to earlier embedded devices |
The Economics of Evolution
The transition away from ROM-based systems wasn't solely due to technological advancement. The ecosystem of support, existing software bases, and certification requirements played crucial roles in determining hardware choices. While modern 32-bit RISC-V chips can be manufactured for less than traditional 8-bit processors, the complete economic picture includes factors beyond mere component costs, such as existing infrastructure and development tools.
This historical perspective on ROM-based x86 systems provides valuable insights into the evolution of embedded computing and continues to influence modern system design principles.