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> classical taxonomy of RISC/CISC dichotomy is basically non-existent nowadays After digest information about IBM 360, I decided, we lost CISCs. One of most im

by simne 3y ago

> classical taxonomy of RISC/CISC dichotomy is basically non-existent nowadays After digest information about IBM 360, I decided, we lost CISCs. One of most important feature of 360 was customizable microcode, which you could load on system boot and got effectively different hardware (like with FPGA emulators of Amiga's). It was widely used to emulate old hardware, like IBM 1401 or IBM 7xxx series. But I have not seen this feature in 390 documentation, so looks like their 360 emulation become just software (and with achievements of semiconductors in 1990s it looks like adequate, to switch to software emulation). I must admit, ARM marketed feature of customized microcode, to add new instructions (they have standardized place in instruction set, named "custom coprocessor instructions", so if you have enough money, you could make special ARM with your additional instructions), but it is nothing if compare to 360.

simne 3y ago
Did you know for what purposes (targets) made mini-computers and why they was limited? When computers first appeared, they was big, just because technology limitations made small machines very expensive to use, so scale used to make computations cheaper. In early 1970s, technology advanced to stage, where become possible to make simplified versions of big computers for some limited tasks, still too expensive for wide use. Simple illustration, IBM-3033 mainframe with 16MBytes RAM could serve 17500 3270 terminals, and PDP of same time could about few tens (may be 50, I don't know exactly), so mainframes even when was very expensive, but given good cost per workplace. Known example, PDP used to control one of scientific nuclear reactor. PDP chosen, not because it have best mips/price ratio, but because it was cheapest adequate machine for this task, so is affordable for limited budget. Very long time, mini machines stay in niche of limited machines, used to avoid much more expensive full-scale mainframes. They used to control industrial automation (CNC), chemical factories and other small things. Once appeared microcomputers (CPU on one chip), first known on wide market in 1977, they begin eat mini's space from bottom, when mainframes continue to become more cost effective (more terminals with appearance of cheap modems, etc) and eat mini's space from top. And in 1990s, when appeared affordable 32-bit microprocessors and became affordable Megabytes of RAM, mini's disappear, because their place was captured by micro's. To be honest, I just don't know anything we could not name microcomputer now, as even IBM Z mainframes are now have single-chip processor and largest supercomputers are practically clouds of SOCs (NUMA architecture). And I must admit, I still see PDP's (or VAX's) on enterprises, where they still control old machines from 1990s (they are very reliable even when limited from modern view, but still work). As I remember, last symmetrical multiprocessor supercomputer was Cray Y-MP, later machines become ccNUMA or just NUMA or even cloud. https://en.wikipedia.org/wiki/LINPACK https://en.wikipedia.org/wiki/LINPACK Unix was simplified version of Multics, system considered to run on mainframes (BTW even exists officially certified Posix Unix for mainframes). You could try mainframes software yourself, it is very affordable now with emulator (sure, be careful about license): https://en.wikipedia.org/wiki/Hercules_(emulator) https://en.wikipedia.org/wiki/Hercules_(emulator) And you will see yourself, how many things borrowed by modern OS's from mainframes. This is nature, people choose simpler, cheaper thing (yes, I don't like x86, my love is 68k).

by simne 3y ago

simne 3y ago

Did you know for what purposes (targets) made mini-computers and why they was limited? When computers first appeared, they was big, just because technology limitations made small machines very expensive to use, so scale used to make computations cheaper. In early 1970s, technology advanced to stage, where become possible to make simplified versions of big computers for some limited tasks, still too expensive for wide use. Simple illustration, IBM-3033 mainframe with 16MBytes RAM could serve 17500 3270 terminals, and PDP of same time could about few tens (may be 50, I don't know exactly), so mainframes even when was very expensive, but given good cost per workplace. Known example, PDP used to control one of scientific nuclear reactor. PDP chosen, not because it have best mips/price ratio, but because it was cheapest adequate machine for this task, so is affordable for limited budget. Very long time, mini machines stay in niche of limited machines, used to avoid much more expensive full-scale mainframes. They used to control industrial automation (CNC), chemical factories and other small things. Once appeared microcomputers (CPU on one chip), first known on wide market in 1977, they begin eat mini's space from bottom, when mainframes continue to become more cost effective (more terminals with appearance of cheap modems, etc) and eat mini's space from top. And in 1990s, when appeared affordable 32-bit microprocessors and became affordable Megabytes of RAM, mini's disappear, because their place was captured by micro's. To be honest, I just don't know anything we could not name microcomputer now, as even IBM Z mainframes are now have single-chip processor and largest supercomputers are practically clouds of SOCs (NUMA architecture). And I must admit, I still see PDP's (or VAX's) on enterprises, where they still control old machines from 1990s (they are very reliable even when limited from modern view, but still work). As I remember, last symmetrical multiprocessor supercomputer was Cray Y-MP, later machines become ccNUMA or just NUMA or even cloud. https://en.wikipedia.org/wiki/LINPACK https://en.wikipedia.org/wiki/LINPACK Unix was simplified version of Multics, system considered to run on mainframes (BTW even exists officially certified Posix Unix for mainframes). You could try mainframes software yourself, it is very affordable now with emulator (sure, be careful about license): https://en.wikipedia.org/wiki/Hercules_(emulator) https://en.wikipedia.org/wiki/Hercules_(emulator) And you will see yourself, how many things borrowed by modern OS's from mainframes. This is nature, people choose simpler, cheaper thing (yes, I don't like x86, my love is 68k).