History of Memory Cards and Industrial Application

By Roger Griesemer, GM memory solutions, Swissbit AG

A History of Memory Cards and Their Industrial Application
Removable storage media – tried and tested and always up to date

Flash memory cards are primarily known in the consumer market as memory for digital cameras, but their importance reaches far beyond that. For more than 20 years, Swissbit has been serving the market for sophisticated industrial systems with flash memory cards as exchangeable system media.

Storage media with NAND chips are notorious for not being infinitely durable when it comes to backup. Unlike HDDs, the number of possible write cycles is limited and strongly dependent on the storage technology used.

When NAND flash became more widespread and attractively priced in the 1990s, people naturally looked for ways to replace vibration-sensitive magnetic HDDs with solid-state NAND flash technology. However, because of its limited lifetime, it only made sense to define a replaceable form factor that would also be much smaller than the 2.5-inch HDD available at that time. In the mid-90s, the CompactFlash card with PATA interface was born.

CompactFlash cards
CompactFlash cards with memory sizes in the megabyte range became popular as storage media in digital cameras, where they provided the required data rate and capacity for image capture. Next, the CompactFlash reader found its way into notebooks because, after all, people wanted to view and edit the images on a larger screen. However, in these applications CompactFlash cards were only an additional, portable storage medium, used as an extension to the HDDs that housed the OS and other software.

The situation is different in industrial applications, for example in automation systems for production lines, in train control systems, in network systems or in casino gaming machines. Here, the CompactFlash card was the obvious choice due to its robustness and insensitivity to motion – unlike rotating storage media. The small format also enabled further miniaturization of industrial PCs. The CompactFlash card (CFC) continued to evolve over the following years. From the Version 1.0 spec to the current Version 6.0, the performance and possible capacity have continuously increased, and the range of features has steadily expanded.

CFast card
Alongside this, there was a change in the interface. Due to the high number of signal lines and the associated large connectors and cables, the parallel data channel used to transfer data from the HDD to the motherboard was replaced by the serial version SATA . The parallel technology subsequently became referred to as PATA. New system controllers have discontinued support for PATA and therefore exchangeable flash media also had to be converted to the new interface. The established and form factor was retained, the interface and connector were replaced, and the new product was launched under the name CFast in 2008.

In the meantime, the SD card had begun its journey to dominate the consumer and photo market. As a result, there were few adaptations of CFast in this market sector. For industrial applications, however, CFast was used in a similar way to CompactFlash cards. Arguments in favor of its use were the higher storage capacities compared to SD memory cards, the greater protection of the electrical contacts vs. touch and contamination, better heat dissipation, a robust form factor that was easier to handle, the continued use of IPC (Industrial PC) housings with a CFC slot, and the higher performance.

The CFast has also undergone a change: from Version 1 featuring a maximum of 3Gb/s to Version 2 offering 6Gbit/s. Peak performance of around 520MB/s is achievable. That’s a factor of 4x faster than the realistic 120MB/s maximum of the CFC.

SATA Module
With SATA, the CFast became competitive in small form factors for the first time. While with PATA there were hardly any alternatives to the rather large 2.5-inch SSDs, the arrival of SATA ushered in the development of several new formats, thanks to the slim interface: SlimSATA Mo-297 with the same connector as 2.5-inch but only half the size and without a housing; the mSATA Mo-300 aimed at the established mini-PCI connector; and then the M.2 modules with lengths of 42, 60 and 80mm. Each of these module types has advantages and disadvantages and all compete with the CFast.

The mSATA and M.2 modules are more cost-effective due to the elimination of a housing and the connector, requiring little installation space. Heat dissipation takes place to the ambient air without an issue. Nevertheless, good reasons for a replaceable medium remain. The mSATA, SlimSATA, 2.5-inch and M.2 variants are suitable for stationary, fixed installation in devices. Since replacement is time-consuming, the SSD must be provisioned so that it lasts as long as possible over the entire period of use. This requires sufficient endurance with SLC technology or more capacity. Both are associated with higher costs.

Advantage of interchangeability
On the other hand, the CFast can be replaced relatively easily. That’s a key consideration in applications, environmental conditions or circumstances that do not facilitate the replacement of an internal storage medium. The cards are touch-protected, no tools are needed to replace them and no ESD protection is required – they can even be replaced when wearing work gloves. Since the cards can be hot-swapped, the time during which the system is not available is minimal. This means that embedded systems and industrial controls, as well as network devices, remain the preferred target applications. In addition, as with the CompactFlash cards, there continues to be applications in casino gaming machines where changes in legislation mean carrying out the complete replacement of software installations more frequently.

Change to the PCIe interface
Innovation is not bypassing the CFast cards. Just as with the change from PATA to SATA, a change to PCIe is imminent. PCIe is the new interface standard for storage products. Data rates of up to 4GB/s are possible with PCIe 3.1 and the new NVMe protocol enables very low latencies in the host drivers and controller firmware. So here, too, it is time to adapt a CFast-style removable media to the new interface technology.

XQD cards
Surprisingly, the first approaches to this again came from professional photography. With the XQD standard, some digital camera manufacturers defined a memory card with a PCIe interface. As early as 2012, the first cameras with a proprietary XQD card came to market. In size, the XQD is between the SD memory card and a CFast card. But in contrast to the SD card, the contacts are on the front side, as with the previous cards, and so are protected vs. physical contact.

CFexpress cards
XQD, which initially supported only a single PCIe lane, evolved into the CompactFlash Association’s CFexpress in 2017, becoming a published standard. To cover different performance requirements, there are slim types with a single PCIe lane (Type A), the XQD-compatible Type B version with two lanes, and a larger 4-lane Type C version. With the 2-lane Type B version, data rates of around 1.5GB/s equating to 4x the CFast performance are possible. It is foreseeable that the CFexpress card will find its way into the same industrial applications as before. Apart from special solutions in the enterprise sector, the number of competing PCIe storage products has diminished compared to the SATA variants. Only the 2.5-inch form factor with the designation U.2, and the M.2 form factor with 2230, 2242 and 2280 lengths (22mm width, 30, 42, 80mm length respectively) are left.

For the CFexpress, the already known arguments apply: 

• Hot-pluggable, therefore low downtime
• Quick change of software installations and licenses from one unit to a replacement unit
• Contact-protected electrical connection contacts
• Closed housing for protection vs. environmental influences
• Safe replacement even under harsh industrial conditions

Since increased performance goes hand-in-hand with increasing heat gen, power dissipation becomes an important issue for memory cards. Often, the housing openings for the memory cards are located near the CPU but there is typically no cooling air flow. As such, the inherent self-heating that occurs during full operation can heat the cards to their spec limits.

When used in industrial applications, it is therefore important to have a thermal management system that keeps the heat development within limits by adjusting the throttling of the data rate without impacting the performance of the system too much. In addition, NAND flash should be used that covers the industrial temperature range of -40°C to +85°C, with particular attention paid to cross-temperatures (different temperatures for writing and reading) to ensure sufficient thermal reserve for heat gen.

SDExpress card
Currently, another candidate is competing for the market of exchangeable media with PCIe interface: the SDExpress card. It combines the SD memory card format and the SD interface with an additional PCIe interface. This makes it backwards compatible with previous SD card applications and at the same time advanced for use in PCIe systems. However, these cards combine the heat gen of 2 interfaces with very small dimensions. It remains to be seen to what extent this standard will become established. The first host systems with chipsets for SDExpress are expected to come onto the market in 2021.

Swissbit into industrial memory products
Industrial applications often have lifespans that exceed consumer applications many times over. It is not unusual for controllers in energy supply systems or train control systems to remain in the field for 20 years and therefore still require the availability of replacement memory cards. As an expert in industry-specific memory products, Swissbit has been supplying optimized cards for demanding applications since the beginning of the CompactFlash era. With CFast, it was one of the drivers to establish the cards in the market, and with CFexpress, Swissbit also supplies cards developed for the embedded market. However, it is not only active at the beginning of the respective gens, but also when the products enter the legacy phase.

Long-term support for legacy systems
What would be incomprehensible in the consumer market is very welcome in the industrial sector: new products in old formats. Just recently, Swissbit launched a family of new CompactFlash cards with the C-500, C-50, C-56 and introduced an SLC low-capacity variant, the C-350, which enables a compatible continuation of earlier gens for particularly long-life applications.

In CFast, the company has just launched the fourth product platform with the F-800, F-80 and F-86, which is targeted at industrial applications and network systems. With several security functions, extended data maintenance, low power consumption and protection vs. data loss in the event of a power failure, this family offers everything that critical applications need.

With the same focus, the Swiss company, which manufactures in Berlin, Germany, is currently introducing the G-20 CFexpress card, available both with cost-effective 3D TLC NAND and as a G-26 with long-term stable 3D pSLC. The G-20 CFexpress Type B offers 2 PCIe lanes and correspondingly performance and, thanks to low power dissipation and optimized temperature management, can operate in the industrial temperature range of -40°C to +85°C.

These examples show that an expert in removable storage media for demanding applications must not only meet the requirements for designing robust products for harsh environments, but also still meet the requirement that originally led to the entry of memory cards into the industrial environment. The memory modules must be durable and, once depleted, easily replaceable.

Throughout the evolution of removable storage media, Swissbit has provided products for industrial applications and continues to offer long-term support for legacy systems. Originally used as a medium for digital photography, CompactFlash cards made their way into railway control systems, network systems and casino slot machines

In favor of CFast are higher storage capacities compared to SD memory cards, greater protection of electrical contacts from the risk of touch and contamination, more efficient heat dissipation and a robust form factor that is easier to handle.

Swissbit is currently introducing the G-20 CFexpress card, available both with cost-effective 3D TLC NAND and as a G-26 with long-term stable 3D pSLC.