While most embedded system components are sourced from OEM-focused manufacturers, portable memory devices are a gray area. The high-volume consumer electronics market – estimated at more than $250 billion annually[1] – creates significant demand for USB flash drives, SD cards, and other consumer-focused portable memory devices. For embedded system designers, the economies of scale these devices offer can be appealing.

But consumer memory manufacturers are primarily focused on the needs of the fast-changing consumer electronics market. In response, a lesser-known category of OEM-focused portable memory systems is providing alternatives that meet requirements unique to non-consumer embedded designs.

Design considerations for portable memory

Access control and rights management, usage monitoring, data logging, in-field firmware updates, and product authentication are just a small sampling of potential applications for portable memory in embedded systems. In addition to the application, the system’s environmental factors and expected use also influence which portable memory solution is the best fit.

As a result, the potential design considerations for portable memory systems are extensive, including:

• Communications interface/protocol
• Connector durability
• Connector footprint/form factor
• Cost
• Data throughput speed
• Environmental ratings
• Ergonomic factors
• Insertion cycle life
• Memory capacity
• Number of write cycles
• Physical size
• Product availability
• Product life cycle
• Ruggedness

Some of these design considerations might be mutually exclusive. For example, small size typically precludes rugged construction. Prioritizing the design considerations makes it easier to determine which features are most important for a particular application.

Benefits of consumer memory in OEM designs

In addition to SD cards and USB flash drives, other consumer memory devices used in OEM designs include Secure Digital High Capacity (SDHC), microSD, and CompactFlash cards. While these NAND flash-based devices are primarily designed for PCs/laptops, digital cameras, cell phones, and MP3 players, the principal benefits intended for consumer electronics can also apply to non-consumer embedded devices.

“Corner-store” availability

The widespread availability of USB flash drives and SD cards makes consumer memory a convenient option. Most users are already familiar with their operation, and it is easy for OEMs and end users to obtain these devices from electronics retailers.

High memory capacity

Transferring data to and from embedded systems often only requires kilobits or megabits of memory capacity, but higher capacities available in consumer memory devices might be required in some cases. Video logging, for example, can require gigabytes of memory capacity. However, some OEM memory devices are now offered in memory capacities of up to 32 GB, so finding devices with high memory capacities is no longer limited to consumer memory.

Low cost

Most consumer memory devices’ upfront cost per bit is low. If an OEM application requires thousands of portable memory devices over the design’s lifespan, cost can be an important consideration.

Small size

Handheld embedded designs often require a small portable memory device to fit in the system. In these applications, a microSD card might be the most attractive option due to its small size.

Overlooked consumer memory considerations

While consumer memory products are not explicitly designed for non-consumer OEM designs, they offer unique benefits. However, these benefits can also have unintended consequences.

“Corner-store” availability reduces control and risks unauthorized access

With hundreds of different models of consumer memory products available, OEMs cannot test, approve, and support every device that physically fits. Despite manufacturers’ attempts to ensure compatibility with specifications like SD, some models might work while others won’t. A lack of control over which devices will work can increase support costs and cause inconvenience for end users.

Additionally, technology standards change. The transition from SD to SDHC provides a recent example – a system designed to use SD cards prior to the release of SDHC will not work with SDHC cards unless the system’s firmware is updated. Likewise, the fast-changing consumer electronics market virtually guarantees that a new technology will emerge in the future with its own compatibility issues (see Figure 1).

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Finally, using a consumer memory device can increase the risk of data theft. For example, a misplaced or stolen USB flash drive that lacks encryption or other security features is vulnerable to unauthorized access, as it easily plugs into any PC. Likewise, using a USB receptacle in an embedded design allows USB flash drives to plug in, which can increase the risk that data could be pulled off the system or that a virus or other malware could be transferred to the embedded device.

High memory capacities are usually unnecessary

Most consumer memory devices today start at 1 GB or higher. As such, embedded systems that require only kilobits or megabits of memory to perform a desired task are essentially paying for capacity they don’t need.

Small physical size is not always preferable

Some designs require a larger portable memory device. For example, in certain military applications, a portable memory device must be able to be easily inserted and removed by a user wearing arctic gloves.

While not always apparent early in the design process, these overlooked considerations should be examined before deciding whether consumer memory meets not only the design criteria, but the expected use as well.

Unique demands of OEM embedded system designs

Non-consumer OEM systems – those intended for use in commercial, industrial, government, medical, military, and other demanding settings – are usually designed to last for years. As a result, portable memory used in these systems must provide long-term availability and reliability. These designs also face demanding environmental conditions and an increased emphasis on secure access. Demands unique to non-consumer OEM designs illustrate why consumer memory devices’ light-duty construction, low cycle life connectors, lack of security features, and short product life cycles can be detrimental to non-consumer applications.

Rugged construction needed in harsh environments

Many non-consumer OEM designs are exposed to harsh environments. Outdoor applications such as military, construction, and agriculture use portable memory devices to transfer operation and maintenance data between the base and vehicles in the field. The memory device could be exposed to vibration, dirt, moisture, shock, temperature extremes, and rough use. Light-duty consumer memory devices and receptacles do not provide sufficient protection or the environmental ratings needed for harsh environments.

Frequent use and long-lasting designs demand durable connector systems

Some applications require a portable memory system with a high mated cycle life rating. Vending machines, for example, can utilize portable memory to provide cashless vending in non-networked environments. A consumer can use the memory device to purchase merchandise from the machine. These machines often see 50-60 cashless transactions per day. Rated at just 1,500 cycles, a USB mating receptacle could wear out in as little as 25-30 days.

Many OEM applications require increased security

Accidental data spillage and computer virus uploads have been under the microscope in the government and commercial sectors in recent years. In response, some government branches and corporations have banned the use of consumer memory devices to decrease these security risks. The widespread availability of USB flash drives and memory cards leaves organizations vulnerable to data theft and malicious viruses.

Long-term availability needed

Consumer memory is driven by the consumer electronics market and therefore subject to short product life cycles and frequent obsolescence. Non-consumer products often have very long product life cycles, so components used in these designs must be available long-term.

Traffic light controllers are an example of long-lasting OEM designs that need a portable memory solution with long-term availability. Technicians use portable memory to upload setup parameters to the controllers. These important pieces of transportation infrastructure can be fielded for a decade or more, so a consumer memory device would likely become obsolete over the controllers’ lifespan.

Portable memory applications that require rugged construction, a high mating cycle life, secure form factors, or long-term availability best exemplify when consumer memory devices should not be considered for embedded designs.

Benefits of OEM portable memory

In response to the unmet needs of many embedded systems, a less familiar category of portable memory devices – OEM portable memory – is emerging with a unique focus on OEMs. These devices provide the rugged construction, high mating cycle life, secure form factors, and long-term availability that consumer memory products do not deliver.

Some portable memory manufacturers produce “industrial” versions of consumer memory products such as industrial CompactFlash cards or industrial SD cards. These so-called “industrial” devices might offer an extended temperature range, use slightly more robust materials, and support a higher number of write cycles. However, they still share many of the drawbacks associated with consumer memory devices: non-robust low cycle life connectors, non-secure form factors, potential obsolescence issues, and a lack of harsh environment ratings.

For the purpose of this discussion, true OEM portable memory devices are defined as purpose-built systems that provide the following features.

Unique form factors and controlled availability for baseline (physical) security

OEM portable memory is most accurately described as a memory system as opposed to a singular device. Figure 2 shows an example of a typical OEM portable memory system, which consists of a receptacle that integrates into a host system and a memory key or token that plugs into the mating receptacle. The token or key will only interface with its unique mating receptacle, which means OEMs only have to test and support one approved device.

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Additionally, unique form factors prevent most unauthorized data transfers, help protect the host system from malicious files, and provide a new potential revenue stream when an OEM becomes the exclusive source of new/replacement keys or tokens.

Truly rugged construction for harsh environments and long-lasting designs

Truly rugged portable memory can withstand extreme temperatures, rough use, sterilization, chemical exposure, static electricity, dust, dirt, moisture, shock, and vibration. To meet these harsh environmental requirements, some manufacturers use a solid over-molding process that encases the electronic components in specially engineered composite plastic materials (see Figure 3).

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The environmental capabilities of portable memory devices do little good unless the receptacle is also protected. Receptacles in OEM memory systems should also carry ratings consistent with the harsh environments in which they will operate, including IP ratings such as IP65 or IP67 or military environmental ratings such as MIL-STD-810. These environmental ratings allow OEM memory systems to operate in harsh environments where consumer memory devices would not survive.

High mating cycle life

OEM memory systems offer a higher number of mating cycles than consumer memory devices, ranging from 50,000 cycles to 200,000 cycles for certain OEM receptacles. For example, an OEM memory receptacle rated at 50,000 insertion cycles would last a minimum of 13.5 years if used 10 times per day. To put that into perspective, a typical USB connector rated at 1,500 insertion cycles that sees the same 10 insertions per day would reach its rated cycle life in just five months. Figure 4 compares consumer and OEM memory device mating cycles.

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Long-term availability

Many OEM memory products have remained unchanged for more than 20 years. Lower-capacity devices have a proven track record of long-term availability, as they utilize Electrically Erasable Programmable Read-Only Memory (EEPROM) or NOR flash non-volatile memory ICs available from multiple manufacturers. This longevity significantly reduces the likelihood that OEMs will have to requalify new memory devices over a system’s lifespan.

Overlooked OEM memory considerations

While OEM memory systems typically do a better job of meeting the unique requirements of non-consumer OEM applications, some design considerations should be weighed against the benefits offered by consumer memory devices.

Impact of the consumer memory market

Unlike low-capacity OEM memory, high-capacity OEM memory typically utilizes NAND flash technology, just as consumer memory products do. As a result, the long-term availability of these high-capacity devices can be affected by the consumer market. However, OEM memory systems based on NAND flash technology typically offer better long-term availability than consumer products by using qualified/consistent sources, utilizing configuration control, and providing built-to-last designs.

Focus on low-capacity applications

Many OEM memory systems are geared toward the low-capacity applications that are more prevalent in non-consumer embedded systems. However, as previously stated, some newer OEM memory systems offer higher capacities that match those of consumer memory products. Most important to engineers is that the chosen memory solution be offered in a range of memory capacities that best meets the system’s specific memory capacity.

Costs

Bit-for-bit, OEM memory is typically more expensive than consumer memory. However, the longevity and consistency that OEM memory systems provide can result in a lower total cost over the system’s lifespan. Compared to consumer memory devices, OEM memory systems reduce the likelihood that OEMs will have to waste valuable engineering time requalifying new memory devices or redesigning their systems because of memory device failure or obsolescence.

Which is better? It depends on the application

Deciding between consumer and OEM is a likely first step in choosing a portable memory solution for an embedded design. In many cases, both will work. For successful OEM designs, however, engineers need to think beyond “Will it work?” and consider the long-term implications and the environment in which the system will be used.

While consumer-focused components are less prevalent in non-consumer OEM designs, it is hard to argue with the convenience, high memory capacity, small size, and low cost that USB flash drives, SD cards, and other consumer devices can provide. Nonetheless, the short life of consumer memory products is inescapably tied to the fast-paced consumer electronics market.

Consumer memory manufacturers are not “anti-OEM”; they’re simply meeting the demands of a consumer market that does not need or care about performance requirements unique to non-consumer OEM applications. When rugged construction, a high mating cycle life, secure form factors, and/or long-term availability are higher priorities, a purpose-built OEM memory system is likely a better fit. For example, Datakey Electronics’ newest series of RUGGEDrive portable memory offers memory capacities up to 32 GB and fast throughput, providing OEM designers with a more reliable alternative to consumer memory products for high-capacity applications in embedded designs.

References

[1] Consumer Electronics: Global Industry Guide, February 2011

Paul Plitzuweit is a business development engineer with Datakey Electronics. He has more than 11 years of experience working in the industrial automation and embedded electronics markets. Paul holds a Bachelor’s degree in Electrical Engineering from the University of Minnesota.

Datakey Electronics 952-746-4066 paulp@datakey.com www.datakey.com