Bill Gates released a scan of the original 1975 Altair BASIC source listing on his own site in April 2025, and internal evidence marks it as the surviving original, not a later reconstruction

On April 2, 2025, Bill Gates published a scan of the original fan-fold paper printout of Microsoft's 1975 Altair BASIC interpreter on his own site (gatesnotes.com) as part of Microsoft's 50th-anniversary observance (The Register, 2025-04-03; Slashdot dateline 2025-04-02). Gates's post described it as "the coolest code I've ever written" — a phrase carried in headline coverage of the release (Windows Central, PCWorld, heise) but not present in The Register's article, and the gatesnotes page itself refuses tooling fetches (403), so the phrase rests on secondary carriage [unverified-quote — needs direct read]. A community mirror, OCR'd to text, is hosted at the Internet Archive as item original-microsoft-source-code; this note's source quote comes from that OCR'd text, fetched directly via extract_pdf.

Several internal features of the document argue it is the actual surviving 1975 listing rather than a later reconstruction. The recurring page header carries "GATES/ALLEN/DAVIDOFF" (clean in roughly forty OCR page headers) under a title the OCR renders only in garbled variants — "BASIC NCS 8980," "BASIC MLS 8080," "BASIC MCS 6080" — whose consistent reading is "BASIC MCS 8080"; the TITLE pseudo-op line itself OCRs as "TITLE BASIC NCS 8980 GATES/ALLEN/OAVLOOFF." A print-queue banner the OCR renders as "PRINTED? 1@eSEP+7S" pairs with the clean date "10-SEP-75" in some thirty page headers. And the header comment's own account of its writing gives the range "FEBRUARY 9 TO APRIL 9" [1975], verbatim in the OCR text — consistent with the well-attested history of Paul Allen's April 9, 1975 flight to MITS in Albuquerque for the first Altair BASIC demonstration. None of these are things a modern forger would need to fabricate consistently across a 157-page OCR'd scan.

This document is the primary artifact behind the header-comment and copyright-notice details discussed in claim-davidoff-wrote-third-of-altair-basic-uncredited, which until this promotion rested only on a 2011 secondary retelling. It is the direct predecessor of the product at the center of claim-gates-1976-open-letter-under-ten-percent-paid.