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Comment by ahartmetz | Hacker News Reader

From the article:

> In 1995, a memory access cost roughly the same as a CPU operation

Uhm... no?!

Here's a CS paper from 1993(!) about prefetching from cache(!!) because the cache was slower than the ALU. https://www.eecs.umich.edu/techreports/cse/93/CSE-TR-152-93....

It would perhaps make Java look a little bad to say that, in 1995, the prevailing attitude in certain circles was "If it's too slow, just wait for faster hardware - Moore's Law forever baby!" (Of course, Sun was selling, at the time, relatively fast hardware - the slower the software, the faster the required hardware)

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Yeah, when I read that, I thought "this guy was either born wayyy after 1995, or he doesn't know the first thing about computer hardware history, or both". 1995 was the year the Pentium Pro was launched, which was (one of?) the first CPU(s) to integrate the L2 (!) cache into the same package as the CPU - they were still separate chips, but the interconnection could be made faster by putting them into the same package.

Yeah, 1995 is much too late. I'd say somewhere about 1990. Maybe you can go as early as the i386 and 68030 in the late 1980s but I'd be hesitant to include them.

Yes, this also stood out to me. I usually think of CPUs and memory having parity in the early 80s, but I never bothered to check for sure. I do remember some early computer architects writing about memory being faster than the CPU!

Early 80s is also what I remember, mainly from articles about old CPUs on HN - like the zero page on the 6502 that served as a sort of L2 register file.

Well, yes but no:

The Z80 took 3 cycles to load from memory. A register to register transfer took 4 cycles (including fetching the instruction). Only one of those cycles was instruction execution.

I think the only reasonably mainstream scenario where the CPU would be significantly slower than memory would be the serial CPU designs such as the PDP-8/s.

That said, at the time people were doing cool stuff with 8-bit CPUs, they weren't running software remotely like what we're discussing here. That would have been done on a VAX, which had instruction and data caches.

What really happened, that the article is alluding to is that memory didn't get much faster in absolute terms since the 1980s. CPUs on the other hand did.

E.g. in the 1980s we had 60ns DRAM. Today DDR5 I believe allows about 10ns random access reads best case (6X). Over the same period CPU clock speeds have increased from about 8MHz to 5GHz (600X).

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