Introduction
As data centers continue to expand in both scale and complexity, operators face the constant challenge of balancing speed, reliability, and cost. Among the different solutions available to connect high-speed equipment, the 100G QSFP28 DAC (Direct Attach Copper) cable stands out as a simple yet highly practical option. Unlike optical transceivers, DACs are passive or active copper cables with QSFP28 connectors on both ends, designed for very short-reach connections. They have become popular in modern server rooms, cloud facilities, and enterprise networks where efficiency and low cost are priorities.
This article takes a closer look at what makes 100G QSFP28 DAC unique, why many operators prefer it for short distances, and how it compares to optical solutions.
What is a 100G QSFP28 DAC?
A DAC is essentially a copper twinax cable terminated with QSFP28 connectors on both ends. The “100G” designation refers to its ability to support 100 Gigabit Ethernet, while “QSFP28” indicates the form factor commonly used in high-speed networking equipment. Unlike transceivers, DACs do not require optical components or fiber cables. Instead, they carry high-speed electrical signals directly over copper, making them plug-and-play with compatible switches, routers, and servers.
The typical reach of 100G QSFP28 DAC cables is between 1 and 5 meters, though some active DACs can stretch up to 7 meters or slightly beyond. While this distance is limited compared to optical fiber, it is usually sufficient for connections within a rack or between adjacent racks, which covers a large percentage of practical deployments.
Why Data Centers Use DACs
The first and most obvious advantage of DACs is cost. Copper-based links are significantly cheaper than their optical counterparts because they avoid the expense of lasers, optical drivers, and fiber cables. For large-scale data centers with thousands of short interconnects, these savings quickly add up.
Another reason is simplicity. DACs are factory-terminated, meaning they do not require cleaning, polishing, or splicing like optical fibers. Technicians can deploy them quickly with minimal risk of misalignment or optical loss. This makes DACs particularly attractive for short runs where simplicity matters more than distance.
Reliability is another strong point. Because DACs transmit electrical signals directly, they do not suffer from optical signal degradation or sensitivity to dust on connectors. This robustness allows operators to treat them almost like traditional copper cables, with less worry about environmental factors.
Performance Considerations
In terms of raw performance, QSFPTEK QT-Q28-PC0.5 100G QSFP28 DACs provide excellent bandwidth and low latency. They support the same 100G Ethernet protocols as optical modules, with latency measured in nanoseconds. For applications where every microsecond counts, such as high-frequency trading or distributed computing clusters, this can be a meaningful advantage.
However, the trade-off is distance. Copper inherently suffers from higher signal loss over longer runs compared to fiber. This is why DACs are limited to short connections, while optical modules can reach anywhere from 100 meters to 80 kilometers depending on type. For this reason, DACs are not replacements for fiber optics, but rather complements in the short-reach segment.
Practical Benefits in Deployment
One aspect that often gets overlooked when talking about DACs is how they simplify the maintenance workflow inside a data center. Optical modules, no matter how advanced, usually require cleaning of the fiber ends, periodic inspection, and replacement if dust or scratches occur. With DACs, technicians deal with shielded copper ends that are much more resistant to dirt or handling errors. This difference can sound minor on paper but in a busy facility with thousands of ports, reducing cleaning cycles and downtime adds up to real savings in both time and labor.
Another point worth noting is the role of DACs in testing and lab environments. Engineers frequently use them during the design or troubleshooting stages because they can be swapped in quickly without worrying about fiber alignment or optical loss. When you need to simulate high-speed interconnects between servers, switches, or routers under real workloads, DACs serve as reliable stand-ins that behave very close to their optical counterparts while being far less fragile.
In terms of energy efficiency, DACs have a small but noticeable advantage. Because they transmit electrical signals directly without the need to convert light to electricity or vice versa, they typically consume less power compared to optical transceivers. For hyperscale operators chasing every watt of savings, this characteristic has made DACs appealing in the short-reach category. Some reports suggest that wide adoption of DAC links in aggregation layers can shave a measurable portion off total rack power draw, which, when scaled across thousands of racks, translates into substantial savings on the power bill.
Another dimension is flexibility in procurement and deployment. Since DACs are relatively low-cost and standardized, organizations often keep extra spares on hand. This means when new servers are added, or a switch is upgraded, administrators can roll out new connections almost instantly without waiting for more specialized optics to arrive. The low barrier to expansion makes DACs a practical choice for companies that grow their infrastructure step by step rather than through massive overhauls.
It is also interesting to see how DAC adoption intersects with cable management practices. Unlike optical fibers, which are thin and light, DAC cables are thicker and less flexible due to shielding. For short runs within a rack or between adjacent racks, this bulk is rarely an issue. But in denser environments, engineers often plan pathways carefully to prevent airflow obstruction. Modern DAC designs, however, have improved in terms of diameter and bend radius, making them easier to handle compared to older generations.
Lastly, DACs contribute to long-term planning by serving as transitional links. Many companies deploy them first to connect systems in early stages and later upgrade to optical modules when distance requirements expand. This staggered approach avoids upfront overspending and gives room for gradual evolution. In this sense, DACs don’t just fill a gap — they help organizations pace their networking investments intelligently.
Conclusion
The 100G QSFP28 DAC is not about replacing fiber optics but about solving a very specific and common challenge: how to connect high-speed equipment efficiently over very short distances. Its strengths lie in affordability, ease of use, reliability, and energy efficiency, which make it an indispensable tool in modern data centers.
As network demands continue to rise, DACs will likely remain a mainstay for short-reach interconnects, bridging servers and switches where fiber is unnecessary and cost-prohibitive. Whether used in hyperscale data centers, enterprise racks, or lab environments, 100G QSFP28 DAC cables prove that sometimes the simplest solution is also the most effective.