Solid State Drives vs. Spinning Disks

It wasn't that long ago that solid state drives (SSDs) were DRAM-based and cost a fortune. Then the proliferation of mobile devices requiring shock and vibration profiles that exceeded hard drives created a huge market for flash. Prices dropped, and with more money available for R&D, the density increased dramatically.

It's been a period of tremendous evolution for flash, but I believe dark clouds are forming on the horizon. Let's start with a little history to help me make my point. I first heard more than 20 years ago that tape was dead, but it took data deduplication to make disk cheap enough to hurt tape sales. So it wasn't disk drives alone that were able to impact tape sales; it was disk drives combined with new technology.

Now we're hearing from some that flash drives are going to replace hard disk drives, and that the cost difference, though great now, will continue to decline. Vendors are putting out charts showing the cost of flash drives and hard disk drives converging, which looks to me like some of the charts I saw for tape and disk more than 20 years ago. I don't think it's going to happen any time soon, and the reasons have to do with lithography limits and disk drive density.

The Limits of Flash Lithography

The main driver of density for flash technology is the size of the lithography used to make chips. I found some good data on Wikipedia, which I confirmed. Here is the change in lithography since 1971, and projected to 2022: