I have multiple computers, some have a 10/100 ethernet adapter while others have a 10/100/1000 ones. If I connect them together with the Cisco sg100-08 switch, do I keep the 1Gbit speed where possible (between two devices at 1Gbit speed) or the whole lan slows down to 100mbit? I checked Cisco website but I couldn't find this kind of information, nor I was able to register to the Cisco support to ask this question (the registration form does not work)
I have dis-assembled a lot of switches over the years, just to see what is really in them.
The SG100-08 (, at least the ones I have seen,) has 2 5-port switch-chips. External ports 1-4 go to chip A, 5-8 go to chip B. The remaining port on each chip is used internally to connect them together.
Each chip can do gigabit between any combination of its 5 ports.
So basically you keep everything at Gb speed unless you are running 4 computers simultaneously in 2 pairs and each pair is split over the 2 chips. (E.g. pair on ports 1 and 5 and a pair on ports 2 and 6 and both pairs doing Gb transfers simultaneously.)
By the way: This dual-chip design is very common in un-managed 8-port switches, regardless which manufacturer made them. (The also very common 5-port variants simply use just 1 of these chips.) Also the 10/100 switches typically follow this basic design. The chip(s) themselves are usually made by Broadcom or AMD.
Each port on the switch is independent, so if a device is 1000Mbit capable, it will operate at that speed.
Any device that operates at 10 or 100Mbit is obviously limited to that speed. The switch will autonegotiate with each device connected.