As the title suggests, there’s no better way to put it. I mean, that’s literally what Western Digital put it as the title. They’ve successfully developed four bits per cell, which they are referring to it as X4. Western Digital has developed 64-layer 3D NAND BiCS3 X4 technology!
First off, a little quick introduction on these terminologies here. SSDs use NAND flash chips. Each NAND flash chip has many cells in it. These cells can be single-level cell (SLC), multi-level cell (MLC, which is actually double-level cell), and TLC (triple-level cell). These number cells represent the number of bits a single cell can hold.
Then comes the second question – how are these cells positioned? A few years ago, we only had 2D NAND flash chips. Recently, there has been development on 3D NAND flash chips, which greatly increases the capacity limit of SSDs.
There are a few hidden characteristics of NAND flash chips. As each cell has a certain write cycle, SLC is always the most reliable – which is why they’re mostly found in server-grade SSDs. As for speed, SLC is also the fastest since it has only one single bit in each cell. However, SLC is always the most expensive and has the littlest capacity.Now, Western Digital has successfully developed this new technology called X4, which is essentially a quad-level cell 3D NAND flash technology in 64-layers, BiCS3 X4 technology. Am I surprised by the development of this technology? Not so much, actually.
Western Digital says that the new BiCS3 X4 technology delivers 768Gb (gigabits!) on a single chip.
QLC is on the other end of the spectrum, as its write cycles and speeds are lower than SLC, but offers the densest capacity per cm², hence having a less painful price tag.
We’ve actually reviewed quite a lot of SSDs here, and most of them are MLC SSDs since it offers a nice balance between speed, reliability, and price. The Plextor M8Se NVMe SSD is the only TLC SSD that we’ve reviewed.
As for Western Digital’s X4 technology, expect to see it in the market sometime later this year or next year.