A port expander is a device that allows one port on a computer system to connect to multiple devices. There are two basic forms of port expanders: internal and external. An internal expander has a connection inside the computer, typically on the motherboard, and the only part the user sees is the expansion plate containing multiple ports. An external device plugs into the existing port and then has multiple places to connect. When not part of a computer system, these devices are commonly known as splitters.
There are no specific types of ports for different computers now days. All the computers from PC to Mac have all the same ports on them. I went to a computer support chat at Eugene Computer Geeks www.eugenecomputergeeks.com and spoke with Cameron fhead geek) and he told me "Well...now day's PC's and MAC's have the same ports. Firewire used to be super popular with MAC's, but a lot of PC's had it as well. Firewire is pretty much phased out now days though."
The advantages of using port expanders are that you get more ports more ports to use. SAS expanders takes one port and makes many out of them. So say you have one 6gbps, and you expand it so you can connect 8 devices. The total throughput on all 8 ports is only 6gbps, or about 80MBPS. Even in regualar hard drives can do 80MBPS, so in theory you could see a bottleneck here,but in practice you probably will be fine. In Some cases SAS expanders are cheaper than getting an equal number of "real" ports.
SSDs are so much faster, often capable of reading 200MBPS or higher, than using a SAS expander with SSDs, you are more likely to cut down performance than you would be a bottleneck in some cases.The disadvantage of a SAS expander is speed. A 3gbps port expanded to 8 or more is not going to be a speed demon by any means. A 6gbps port expanded to multiple ports will perform better, but may still be a bottleneck in some cases.
Some disadvantages are alot of them are external and that can be annoying and get in the way could use more power and if your power source isn't good enough it could cause problems when you add more devices it takes up more power. The power source can only handle so many extra ports. I asked Cameron (head geek) "What happens with the power source if you over load it do u plow the power source or what?" Cameron said "That the computer won't turn on usually if you unplug things it will turn back on again. It could possibly destroy the power source but not likely. Another disadvantage of using port expanders is having to buy a port expander.