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Arthur T Knackerbracket has found some questions regarding a story we covered on Wednesday, in which Intel and Micron jointly announced their 3D XPoint memory. However, some are now asking how this can actually be used because the promised data rates far exceed anything with which current motherboards can cope. Some thoughts follow:

The 3D design uses a transistor-less cross point architecture to create a 3D design of interconnects, where memory cells sit at the intersection of word lines and bit lines, allowing the cells to be addressed individually. This means data can be read or written to and from the actual cells containing data and not the whole chip containing relevant cells.

Beyond that, though, we don't know much about the memory, like exactly what kind of memory it is. Is it phase change memory, ReRAM, MRAM or some other kind of memory? The two won't say. The biggest unanswered question in my mind is the bus for this new memory, which is supposed to start coming to market next year. The SATA III bus used by virtually all motherboards is already considered saturated. PCI Express is a faster alternative assuming you have the lanes for the data.

Making memory 1000 times faster isn't very useful if it chokes on the I/O bus, which is exactly what will happen if they use existing technology. It would be like a one-lane highway with no speed limit.

It needs a new use model. It can't be positioned as a hard drive alternative because the interfaces will choke it. So the question becomes what do they do? Clearly they need to come up with their own bus. Jim Handy, an analyst who follows the memory space, thinks it will be an SRAM interface. SRAM is used in CPU caches. This would mean the 3D XPoint memory would talk directly to the CPU.

"The beauty of an SRAM interface is that its really, really fast. What's not nice is it has a high pin count," he told me.

He also likes the implementation from Diablo Technologies, which basically built SSD drives in the shape of DDR3 memory sticks that plug into your motherboard memory slots. This lets the drives talk to the CPU at the speed of memory and not a hard drive.

One thing is for sure, the bus will be what makes or breaks 3D XPoint, because what good is a fast read if it chokes on the I/O interface?

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