pgc+@andrew.cmu.edu (Paul G. Crumley) (08/06/87)
Hello, Normally I don't respond to these types of flames but this time I will make an exceptiom lest someone get the wrong idea about 370s. If you see similarities between the 370 and the 80X8X architectures (it almost makes me ill to associate the terms architecture and 80X8X!) your knowledge about these systems IS very limited. Though the 370 is not considered to be the BEST architecture by many people, it is very versatile. For an architecture that is over 20 years old, I think it has aged very gracefully. Just to give you the flavor of the 370 architecture here are some of its components: 16 General Purpose Registers -- Having written lots of assembly language for these beasts I can tell you there are plenty of registers to use. I don't think that humans could really deal with more in a consistently good manner though I realize today's optimizing compilers might be able to use more registers. BTW, these are not divided into two sets of eight, one set data, one set address, like the 680X0 thus allowing you or the compiler to use them as use see fit. Rich set of Data Types -- The 370 operates on 16, 32 and for some instructions (Mult, Div) 64 bit quantities numbers, Zoned Decimal Numbers (ASCII & EBCIDIC), Packed Decimal Numbers (BCD), Characters, and Floating Point Numbers. Bit strings are about all that is missing from this architecture. Useful Addressing Modes -- About the only modes missing are the Auto-IN/DEcrement addressing modes. Large, Flat Address Space -- Early models had 16M bytes of flat space, newer models have 2^31 (I think this is right) bytes. Orthogonal Instruction Set -- This machine doesn't do silly things like mess up the EOR addressing modes. "Robust"ness -- This machine has everything needed to implement Virtual Machines, restart instructions after internal processor errors, handle virtual memory, ..... These are REAL machines that can recover from errors and keep going. Well Defined I/O Channels -- There are standard, high-speed ways to attach devices to these machines. True Compatibility between Models -- There aren't ANY user-level instructions that behave differently on different models. This is one of the reasons that these machines have spread around the world, especially in business environments. You really CAN run the same program on a 370, 43XX, 308X, etc, without even recompiling! Opinion: The 370 is a versatile and robust architecture that has proven itself over time. Though some architectures do have additional features such as more addressing modes, more data types, language specific instructions, etc., the 370 has shown its ability to efficiently run programs in as varied languages as FORTRAN, C, Lisp, COBOL, PL/I, and APL. I believe this shows what a good job the original designers of the 370 did in including the important features and shying away from the exotic (though the EDIT UNDER MASK and EXECUTE instructions are pretty exotic). I have seen benchmarks of the 370's performance with the use of some of the new optimizing compilers (such as those used with RISC) and it is impressive what these machines can do. In short, any comparison of the 370 and the 80X8X is probalbly lacking in the similarities column and well populated in the differences column. If you would like more information please do not hesitate to contact me. Best Regards, Paul G. Crumley Hardware System Designer CMU/ITC