Is there a tangible difference in speed/latency between a managed and unmanaged network switch?
Good question. The short answer: No, there's no inherent difference in the speed or latency available to hosts talking to one another on a managed vs. unmanaged switch. In reality though, you'll generally see better performance all around on a managed switch, because unmanaged switches are typically less capable in every sense when compared to a managed switch.
The long answer: Most switch manufacturers provide specifications that often include backplane speed, data rate, and throughput.
- A backplane is essentially a switch's motherboard. So backplane speed is the speed to which a switch or logical stack of switches is limited by its hardware.
- The data rate, sometimes referred to as bandwidth, is essentially the theoretical bandwidth at which a switch can process frames. If the data rate is expressed in full duplex that means it's considering both ingress and egress traffic on each interface simultaneously.
- Lastly, the throughput, or forwarding rate, of a switch is an expression of the amount of data that can be moved from one place to another in a given amount of time. That's why switches' throughput is typically expressed in some multiple of packets per second, or in the case of an unmanaged switch, frames per second.
So the long answer really is, you need to compare specific switch models - look at the spec sheets and see for yourself!
Most switching is performed in hardware at wirespeed, so no, you will not normally see any difference in the speed or latency for standard layer-2 switching.
If the managed switch is a layer-3 switch, it may be possible that there are some features being used that can affect the latency for the layer-3 routing (not possible on an unmanaged switch), but in an apples-to-apples comparison, the layer-2 switching should perform the same.
An unmanaged switch comes w/ a fixed configuration, which means that there's no way to reduce network overhead, whereas a managed switch will allow for traffic prioritization through the use of SNMP, VLANs, QoS, etc. Spanning Tree Protocol, VLAN tagging/trunking also have the ability to create a more streamlined network process. While a straight vanilla setup of both appliances may produce similar results, the granularity provided for via managed switches should ultimately allow for greater throughput and reduced latency. Network monitoring tools will also help in this regard, as a managed switch will allow for configuration changes based on observed results, while an unmanaged switch will not. This is especially true in the enterprise.