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It's an interesting question whether, over the long term, quantum hardware will match the feature of classical hardware where memory is significantly cheaper th
by Strilanc 6y ago
It's an interesting question whether, over the long term, quantum hardware will match the feature of classical hardware where memory is significantly cheaper than compute-capable bits in the CPU. Hard drives are 100x cheaper per bit than RAM which is 100x cheaper (I think?) per bit than a CPU register.
How expensive is quantum memory relative to quantum compute, over the long term? Expectations about the answer to this question strongly affect whether or not you find this paper relevant. And the answer depends on the pieces you build your quantum computer out of, e.g. hypothetical photonic architectures have a bigger ratio than hypothetical superconducting qubit architectures.
It is currently very much an open question whether or not quantum computers will have a memory hierarchy.
- thesz 6y agoYou are off by orders of magnitude. The difference in memory density between DRAM and SRAM (register file) is not 100 times, more like 10x. Standalone "registers" - memory elements of pipelines, state machines etc, - are again not more than ten times less denser than SRAM. After DRAM goes SSD and after SSD goes disk. The difference in price per GB for SSD and disk is about four (4x) times, I looked for that numbers recently. The difference between tape and disk is, again, about 4-10 times (from memory).
- Strilanc 6y agoAre you sure? I was just going off a quick search of Amazon, where 1 GB of ram cost ~30$, 1 TB of disk cost ~50$, and a CPU with ~1MB of L2 cache cost ~200$. Based on that I actually thought 100x was a comfortable underestimate, not an overestimate.
- dcow 6y agoCPU cost is not dominated by the cache size is the problem, I think.
- robocat 6y agoBut I think that cache is roughly 50% of marginal production cost of the silicon chip die by mm2. https://cdn.wccftech.com/wp-content/uploads/2020/11/AMD-Ryzen-5000-Zen-3-Desktop-CPU_Vermeer_Die-Shot_1-scaled.jpg https://cdn.wccftech.com/wp-content/uploads/2020/11/AMD-Ryze... https://images.anandtech.com/doci/16214/Zen3_arch_19.jpg https://images.anandtech.com/doci/16214/Zen3_arch_19.jpg
- thesz 6y agoCache is not memory, it is more complex - LRU and all that, often with several access ports (quadratic space dependence). SRAM is memory that is on-die and it is much cheaper.
- Dylan16807 6y agohttps://en.wikipedia.org/wiki/EDRAM https://en.wikipedia.org/wiki/EDRAM If the price/density difference was anywhere near that much you'd see a lot more chips with fat onboard DRAM caches.
- thesz 6y agoWhy don't you compare 1TB of DRAM with 1TB of hard disk? Also, please consider bandwidth here. 1TB of RAM can max at ten times the bandwidth of 1TB SATA hard disk drive, if not more. The difference in price is 80-fold, but if you factor in bandwidth requirements, the price difference drops to lower levels (10 drives, more SATA or specialized controllers, etc).