Things were different in the 1970s. And perhaps that explains why IBM is more secretive now. The Itel AS/5 was a clone of the IBM System 370 Model 158, a very

Things were different in the 1970s. And perhaps that explains why IBM is more secretive now. The Itel AS/5 was a clone of the IBM System 370 Model 158, a very popular mainframe for its time. How was Itel able to clone it? Simple. Just use the hardware schematics! http://www.silogic.com/NAS/NAS.html http://www.silogic.com/NAS/NAS.html 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. I had personal experience with the AS/5. It came supplied with IBM schematics and microcode listings. These were kept in giant binders in the machine room. When the machine booted up, a Z80 based processor that Itel designed was used to load IBM microcode into the clone mainframe. Oh, and the application software that ran on that 1970s machine will still run on IBMs latest mainframes. When IBM introduced the PC in 1981, hardware schematics and BIOS listings were also available for purchase. Times have changed!