To develop a legal BIOS, Phoenix used a clean room design. Engineers read the BIOS source listings in the "IBM PC Technical Reference Manual". They wrote technical specifications for the BIOS APIs for a single, separate engineer—one with experience programming the Texas Instruments TMS9900, not the Intel 8088 or 8086—who had not been exposed to IBM BIOS source code. The single engineer developed code to mimic the BIOS APIs. By recording the audit trail of the two groups' interactions, Phoenix developed a defensibly non-infringing IBM PC compatible ROM BIOS. Because the programmers who wrote the Phoenix code never read IBM's reference manuals, nothing they wrote could have been copied from IBM's code, no matter how closely the two matched. This reverse engineering technique is commonly referred to as a "Chinese wall".