If you are on a modern 64-bit Windows (10 or 11), you must use a 32-bit client

: Users often use Oracle 10g or 11g clients as backward-compatible alternatives for connecting to older databases on newer Windows versions.

A bespoke manufacturing or logistics application from 2002 was compiled against the Oracle 8.1.7 libraries. The original vendor is bankrupt. The source code is on a zip disk in a drawer. The company has two choices: Find this client, or re-write a million lines of undocumented code. They choose the hunt.

: Users with a valid support contract can request old software versions directly from Oracle Support . They are often the only official source for archived versions.