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A comment on Factoring 2048 RSA integers in 177 days with 13436 qubits and a multimode memory. Parent comment

Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by thesz on Tuesday March 23, 2021 @11:42AM (#26556343)
You 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).

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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by Strilanc on Tuesday March 23, 2021 @12:36PM (#26556976)
Are 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.
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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by dcow on Tuesday March 23, 2021 @01:25PM (#26557587)
CPU cost is not dominated by the cache size is the problem, I think.
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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by robocat on Tuesday March 23, 2021 @01:56PM (#26558007)
But 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-Ryze...

https://images.anandtech.com/doci/16214/Zen3_arch_19.jpg

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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by thesz on Tuesday March 23, 2021 @02:59PM (#26558881)
Cache 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.
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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by thesz on Tuesday March 23, 2021 @10:11PM (#26562767)
Why 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).

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Re:Factoring 2048 RSA integers in 177 days with 13436 qubits... by Dylan16807 on Tuesday March 23, 2021 @05:18PM (#26560535)
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.

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