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Thanks I was familiar with the historical importance of IBM's System/360 but what is connection between System/360 and RISC-V? That was what I didn't understand

Thanks I was familiar with the historical importance of IBM's System/360 but what is connection between System/360 and RISC-V? That was what I didn't understand in the OP's comment.

PaulHoule 7y ago
The "360" in System/360 meant "General Purpose" or "Scalable". That is, you could get it in many different sizes and expect that you could buy a bigger one in the future that is compatible with your old programs. Contrast that to DEC, which had a PDP-8 that was comparable to the smallest 360 but cost about 1/5 as much. If you needed something better you needed to upgrade to the PDP-10 or PDP-11, neither of which was compatible with your PDP-8 programs. PDP-11 was wildly popular but it had no path to 32-bit, so DEC introduced the VAX architecture... Each need to go to an incompatible system was a chance to switch vendors, and that could be one reason IBM is still here and DEC isn't. Today the x86, POWER, and ARM architectures have all had long rides of continuous improvement, so the scalability ideas of the 360 are mainstream. RISC-V takes scalability to the next level, targeting various "backwater" areas such as storage controllers. Now that we have SSD's the processors in storage controllers can't keep up with the math to do RAID. Intel's "Rapid Storage Technology" doesn't seem like a scam anymore because there is so much excess power in the Intel architecture compared to the junk that is in contemporary storage controllers. RISC-V could create a huge market for chips that are scaled down in the ways they need to be scaled down, but scaled up in the ways they need to be scaled up. For instance that storage controller might need to be wicked fast, but it doesn't need floating point and it doesn't need virtual memory. RISC-V lets you pick and choose features but still stick with the some toolset for building code; thus you could port some software between chips with different capabilities.
- detaro 7y ago
  In what ways is RISC-V set up to do that better than e.g. ARM? Just the free ISA meaning different companies can specialize better on different segments, or are there novel technical design choices that enable that?
  - PaulHoule 7y ago
    Mainly the free ISA. The RISC-V ISA does not have new and deep ideas in it (like the Mill) but because it is utterly conventional it is able to build on experience and do a number of little things right that help with performance, power, area, simplicity, etc.
- bogomipz 7y ago
  Thanks for the detailed response. That makes sense - the idea of "modularity" is certainly a design goal of RISC-v. I was curious about this however: >"Now that we have SSD's the processors in storage controllers can't keep up with the math" I haven't looked at hardware RAID boxes in quite some time. I guess I was kind of surprised that this would be an issue. Isn't the math involved just computing the parity of each stripe? Am I overlooking something obvious?

Thanks I was familiar with the historical importance of IBM's System/360 but what is connection between System/360 and RISC-V? That was what I didn't understand in the OP's comment.

PaulHoule 7y ago

The "360" in System/360 meant "General Purpose" or "Scalable". That is, you could get it in many different sizes and expect that you could buy a bigger one in the future that is compatible with your old programs. Contrast that to DEC, which had a PDP-8 that was comparable to the smallest 360 but cost about 1/5 as much. If you needed something better you needed to upgrade to the PDP-10 or PDP-11, neither of which was compatible with your PDP-8 programs. PDP-11 was wildly popular but it had no path to 32-bit, so DEC introduced the VAX architecture... Each need to go to an incompatible system was a chance to switch vendors, and that could be one reason IBM is still here and DEC isn't. Today the x86, POWER, and ARM architectures have all had long rides of continuous improvement, so the scalability ideas of the 360 are mainstream. RISC-V takes scalability to the next level, targeting various "backwater" areas such as storage controllers. Now that we have SSD's the processors in storage controllers can't keep up with the math to do RAID. Intel's "Rapid Storage Technology" doesn't seem like a scam anymore because there is so much excess power in the Intel architecture compared to the junk that is in contemporary storage controllers. RISC-V could create a huge market for chips that are scaled down in the ways they need to be scaled down, but scaled up in the ways they need to be scaled up. For instance that storage controller might need to be wicked fast, but it doesn't need floating point and it doesn't need virtual memory. RISC-V lets you pick and choose features but still stick with the some toolset for building code; thus you could port some software between chips with different capabilities.

detaro 7y ago
In what ways is RISC-V set up to do that better than e.g. ARM? Just the free ISA meaning different companies can specialize better on different segments, or are there novel technical design choices that enable that?
- PaulHoule 7y ago
  Mainly the free ISA. The RISC-V ISA does not have new and deep ideas in it (like the Mill) but because it is utterly conventional it is able to build on experience and do a number of little things right that help with performance, power, area, simplicity, etc.
bogomipz 7y ago
Thanks for the detailed response. That makes sense - the idea of "modularity" is certainly a design goal of RISC-v. I was curious about this however: >"Now that we have SSD's the processors in storage controllers can't keep up with the math" I haven't looked at hardware RAID boxes in quite some time. I guess I was kind of surprised that this would be an issue. Isn't the math involved just computing the parity of each stripe? Am I overlooking something obvious?