Ferranti ULA Design Documents for Sinclair Computers Surface

In the early 1980s the Sinclair computers were the cheapest on the market, and a key to that was the Ferranti ULA, a type of ASIC built from a library of logic parts. A recent find on eBay turned up a trove of original Ferranti design documents that cover every Sinclair product of that era, from the ZX81 and Spectrum to the ZX printer, the Microdrive, the Spectrum Interface 1, and even a small flat‑screen TV. The documents include printed sheets, engineering drawings and handwritten notes, and they reveal details that had not been fully reverse‑engineered before. Sky, which now holds the intellectual property rights, has allowed the files to be shared with minimal changes because of their historical importance. The documents are catalogued with download links in a Google spreadsheet, so anyone can look them up.

The most intriguing part of the archive is the set of ULAs that have not yet been reverse‑engineered. Engineers who built the original chips left subtle differences between versions in the drawings, showing how they patched bugs over time. Those differences are now available for researchers to study, potentially shedding new light on how Sinclair achieved such high performance with limited hardware. The release also includes a brief video that explains how the Ferranti ULA works, giving context to the raw technical drawings. With the files online, hobbyists and historians can finally examine the inner workings of these iconic computers.