01-04-2021 | | By Sam Brown
Recently, Micron announced that it is dropping the development of 3D Xpoint memory in favour of CXL. What is 3D Xpoint, what is CXL, and why is Micron changing tact?
3D Xpoint memory is a non-volatile memory technology that was developed by Intel and Micron. The technology, unlike NAND FLASH, allows for individual bits to be accessed which can provide it enhanced performance over NAND (which has to have entire blocks erased before bits can be altered).
The memory technology utilises bulk resistance to store data, and while the exact material used between bit lines has not been publicly stated, what is known is that the technology utilises Chalcogenide glass. The bits are arranged so that each bit has two metal connectors (top and bottom), and a current is passed through one of the connectors. The resistance of the channel is measured, and this indicates the state of the bit.
3D Xpoint memory is also vertically stacked allowing for increased memory densities, and the resulting structure is stated to provide significantly faster performance over NAND FLASH including lower latency, higher bandwidth, and a greater number of write cycles. The brand name sold by Intel is called Optane, and while the actual performance against the predicted performance fails to reach the mark, the memory technology is still one of the fastest available.
Compute Express Link, or CXL, is an open-source memory standard that describes a system for connecting CPUs to memory and devices to maximise speed, reduce latency, and ensuring that shared resources are coherent. The standard utilises the PCIe physical and electrical interface with multiple protocols for different tasks including I/O, memory, and cache coherence.
Such technology is becoming increasingly important in large data centres which are required to run large models including simulations and AI. Since such systems require the use of shared resources, and different processes can change these shared resources, coherence systems such as software stacks can increase complexity and use up valuable resources. The use of CXL not only frees up system resources, but also allows developers to focus on targeting workstations.
Recently, Micron announced that it will be dropping its development and sales of 3D Xpoint memory in favour of Compute Express Link. While faster memory with lower latency is one method for improving system performance, the use of CXL can also have the same effect with older memory technology.
According to Micron, the development of 3D Xpoint technology uses proprietary CPU-to-Optane PMEM links whereas CXL uses an open standard. The use of open standards lowers the barriers to entry for developers of computing systems, and allows for Micron to focus on addressing data-intensive workload environments.
Furthermore, Micron also stated that Optane technology requires complex changes to existing systems for them to be able to take full advantage of Optane technology, while implementing CXL does not. However, Micron backing out of 3D Xpoint has not deterred Intel from pursuing Optane memory as the next generation of non-volatile memory.