Comments on: Understanding SLC, MLC, TLC, and QLC NAND Flash | Learning to Run with Flash 2.0

By: Anshul Rana

Anshul Rana — Fri, 06 Feb 2026 13:37:46 +0000

3D-IC stacks full dies and connects them with TSVs or hybrid bonding to shorten signal paths.

3D NAND uses the same vertical idea, but stacks memory cells inside one die instead of stacking logic wafers. The controller stays separate, which is why NAND scales density so well.

Your “fireman’s pole vs staircase” comparison fits perfectly for explaining why vertical connections matter.

By: Tom Greiner

Tom Greiner — Tue, 03 Feb 2026 05:22:31 +0000

3D-IC is a three-dimensional integrated circuit (IC) built by vertically stacking different wafers together into a single package. Within the 3D-IC package, the device is interconnected using through-silicon vias (TSVs) or hybrid bonding. TSVs are like a firemans pole between floor levels, much faster than the staicase.

By: Les Tokar

Les Tokar — Thu, 23 Oct 2025 15:00:17 +0000

In reply to Christian Bau. There is much literature with respect to QLC with pseudo-slc so yes we can verify such. With respect to write endurance, I dopn't think you will ever find anything with respect to the pseudo-SLC alone, but rather, there are always listed metrics for the drive as a whole. We typically don't speak to pseudo-slc within NAND as it has become a very common thing.

By: Christian Bau

Christian Bau — Thu, 23 Oct 2025 14:49:51 +0000

I bought a Crucial X6 2TB drive for my Mac and performed some measurements because I was quite curious about thd actual performance. When filling the empty drive with 700 GB from an older drive, about 350 GB were copied at about 1GB/sec, then the speed dropped below 30MB/sec. After leaving the drive alone for an hour or two it was back to full speed. So it seems this is a QLC drive with pseudo-SLC cells, which would explain my observations.

Could you verify that QLC drives also come with pseudo-SLC cells, and do you have any numbers on the write endurance of pseudo-SLC? Thank you.