Storage Class Memories (SCM) -- I/O devices are now fast and expensive, not CPUs

[Brad Pierce]

For the entire careers of most practicing computer scientists, a fundamental observation has consistently held true: CPUs are significantly more performant and more expensive than I/O devices. The fact that CPUs can process data at extremely high rates, while simultaneously servicing multiple I/O devices, has had a sweeping impact on the design of both hardware and software for systems of all sizes, for pretty much as long as we've been building them.

This assumption, however, is in the process of being completely invalidated.

The arrival of high-speed, non-volatile storage devices, typically referred to as Storage Class Memories (SCM), is likely the most significant architectural change that datacenter and software designers will face in the foreseeable future. SCMs are increasingly part of server systems, and they constitute a massive change: the cost of an SCM, at $3-5k, easily exceeds that of a many-core CPU ($1-2k), and the performance of an SCM (hundreds of thousands of I/O operations per second) is such that one or more entire many-core CPUs are required to saturate it.

This change has profound effects:

1. The age-old assumption that I/O is slow and computation is fast is no longer true: this invalidates decades of design decisions that are deeply embedded in today's systems.

According to https://queue.acm.org/detail.cfm?id=2874238

 

[Pawan Fangaria]

Along with core memory speed, these days there has been great emphasis on improving memory access mechanisms where the data can be pre-fetched (DDR3, DDR4,... are examples). So, in coming days it wouldn't be a wrong expectation to have equalization in computation and memory storage and access speeds.