US companies also copied the IBM 360. RCA did, perhaps others. US companies also copied the IBM 370. I used a far superior clone computer called the Itel AS/5.

US companies also copied the IBM 360. RCA did, perhaps others. US companies also copied the IBM 370. I used a far superior clone computer called the Itel AS/5. Much of the hard work was actually trivial because: ALD's were Automated Logic Diagrams. IBM sold these. They were complete schematics for the S-370. EXSYSCO basically duplicated the logic of the S-370. http://www.silogic.com/NAS/NAS.html http://www.silogic.com/NAS/NAS.html These schematics were freely available in the machine room. I remember perusing them at night when things were slow. Microcode listings were also freely available. (I believe a large part of IBM's openness at the time was because of antitrust litigation). I also remember seeing the Itel engineers using the IBM schematics when debugging problems.