(previously I wrote) >> The book "Computer Architecture: Concepts and Evolution" by >> Blaauw and Brooks has many descriptions on how instructions got >> to be the way they did.
>> (Blaauw was the main designer of S/360... > I thought that Gene Amdahl was the principle architect of 360. > A search to check my facts seems to reveal that Amdahl, Blaauw > and Brooks led the design team. I don't know the actual hierarchy, but yes it was those three. My feeling was that Blaauw made the higher level decisions (should we have an EDIT instruction) and Amdahl the lower level decisions (can we really implement this, how many digits can it do, etc.) Both are pretty important. Brooks, at least as described in "Mythical Man Month," led the OS/360 project. In the above mentioned book Blaauw takes the blames for what he considers his mistake in adding the EDIT instruction. As to programming, microcode is now usually considered firmware, though the term is likely more recent than S/360. The microcode of most S/360 models was actually hardware, physical capacitors or transformers. The floppy disk was origially meant to load the microcode store in S/370 models, replacing the hardware microcode storage. More recently, hardware is designed in verilog or VHDL, hardware descriptor languages. Logic gates can be written out as easily as software. As the cost of masks has increased, hardware is more often done through programmable logic where bits activate gates on a chip. Even more, there are system that allow for dynamic reconfiguration, the hardware equivalent of self-modifying code! -- glen
