Total maximum memory capacity
Some process computers provide much more than others…
Remanent memory fulfils two different but interrelated tasks. It is usually responsible for booting the operating system. This means that its loss – commonly caused by vibration – renders the system unfit for use. The second role involves storing information.
Since the original Raspberry Pi, microSD or (previously) fullsize SD cards have been used. While inexpensive, using them has disadvantages. Firstly, most SD cards have short lifetimes. Back in the halcyon days of the original Pi, we ran a cluster, and the most common failure was that the cards overheated and physically broke apart. While industrial-calibre memory cards are available, they are significantly more expensive.
Secondly, many process computer companies – the Raspberry Pi Foundation is an especially poor example – tend to use the cheapest possible memory card holders. In the case of the Raspberry Pi, the mechanically locking units were replaced by friction-fit-based ones, which are less robust when it comes to vibration. Finally, microSD cards have limited storage capacity – larger formats fit more chips.
The availability of cheap USB cases simplifies life here – pop in a leftover SSD and connect to a USB 3.0 port to get relatively high performance. Sadly, these will eventually suffer from problems, given that USB connectors are not known for vibration robustness. A sturdier approach involves memory soldered directly on to the process computer. While it can’t be exchanged at the end of its write cycle allowance, vibration doesn’t affect it.
The Udoo Vision dominates this area. Its pricey high-end model comes with 64GB of storage soldered in. The Orange Pi 3B takes a similarly innovative approach via its eMMC module (shown above), available in capacities from 16GB to 256GB. A similar eMMC slot can be found at the bottom of the Rock 5B.
Another innovation is the use of an M2 slot. This permits the use of workstation SSD memory, commonly used in laptops and ideally suited to heavy write loads. Furthermore, the cards can usually be screwed to the main PCB, improving the overall vibrational robustness.