AOC (Active Optical Cable) and DAC (Direct Attach Cable) are both types of cables used in data center and high-performance computing environments to connect networking equipment. While both serve similar purposes, there are key differences between the two: 

1. AOC (Active Optical Cable):

• Technology: AOCs use optical fibers to transmit data. They contain optical transceivers on each end of the cable to convert electrical signals into optical signals for transmission and vice versa.

• Distance Reach: AOCs are suitable for longer-distance connections compared to DACs. They can support distances ranging from a few meters to over 100 meters.

• Flexibility: AOCs are generally more flexible and lighter than DACs, making them easier to handle and install in tight spaces.

• Applications: Commonly used for high-speed data transmission in data centers, enterprise networks, and storage area networks.

2. DAC (Direct Attach Cable):

• Technology: DACs use copper cables to transmit electrical signals directly between devices without the need for optical transceivers. They often have SFP or QSFP connectors on each end.

• Distance Reach: DACs are suitable for relatively short-distance connections, typically within the range of a few meters to around 10 meters.

• Flexibility: DACs are generally less flexible and heavier than AOCs due to the use of copper conductors.

• Applications: Commonly used for short-distance, high-speed connections within racks or between closely located networking equipment in data centers.

DAC/AOC Cables Comparison

DAC cables are used to connect switches, servers, and storage inside racks, while AOC cables are mostly used to link switches, servers, and storage between different racks inside data centers. Besides this, DAC AOC cables differ from each other in the following aspects.

Power Consumption

Normally, the power consumption of AOC cables is higher than DAC ones, which is 1-2w. While the power consumption of DAC active cables is less than 1w, and the passive ones cost nearly no power consumption at the value of lower than 0.15w due to the thermal design of direct attach copper cables. As a result, the operating expenses on power consumption will be decreased when adopting the DAC options.

Transmission Distance

Adopting optical fiber technology, AOC cable can transmit over longer distances—100 m, while DAC cable link length limit is 10 m (passive DAC: 7 m; active DAC: 10 m). To sum up, DAC cabling solutions are suitable for short-range transmissions, while AOC solutions are applied in long-range networking cases.

Note: the max. distance of a signal that can be transmitted via a DAC cable change depending on the data rate. The link length will decrease as the data rate grows, for example, 100G DAC cables can only transmit up to 5 meters.

Cost

Roughly speaking, DAC has a relatively simple internal structure with fewer components, and the copper cables are much cheaper than fiber cables. When implemented in large-scale data centers, the sum of money will be saved for large quantities of DAC cables compared to AOC options. DAC indeed provides a cost-effective solution over AOCs for short-range applications, but for long-range applications, it's wise to have the overall costs list by comparing these two options.

EMI Immunity

Electromagnetic interference (EMI), refers to a disturbance generated by an external source that will affect the electrical circuit. As mentioned before, the active optical cable contains optical fibers—a kind of dielectric that can't conduct electric current. Therefore, AOC cables are immune to electromagnetic interference, which can be used in most situations. However, due to the nature of copper with sending electrical signals, direct attach copper cables are vulnerable to the effects of EMI. Thus, the environment is important to avoid undesirable responses, degradation, or complete system failure.

In summary, the primary difference lies in the technology used for data transmission. AOCs utilize optical fibers and active electronics for longer-distance transmission, while DACs use copper conductors for shorter-distance connections. The choice between AOC and DAC depends on the specific requirements of the networking environment, including the distance between devices and the desired data transmission speed.