I've got one desktop hard wired to my router and two that use old Belkin PCI wireless adaptors. These two "wireless" computers operate with about half the connection speed as my wired computer. Is this loss of speed inherent in the adaptors or is it partly or entirely a function of signal strength? In other words, would boosting the signal strength likely improve the connectivity speed?
A wired connection will always give you a better connection speed than wireless. An ethernet port in the rear of the router is a gigabit connection and the wireless connections are at about 300 mbs. If you have a N router and your old pci adapters are G band then that's why your getting a lower amount of wireless bandwith.
There are new routers out now that can give you the same connection speed as a wired connection and it's called AC which is the next higher band then a N router.
I don't think it's possible to boost the signal strength , you can extend the range of the wireless signal but not boost the strength.
I have an Actiontec MI24WR wireless router, version D, which I believe is good for 802.11b/g but not "n". I think it can be upgraded to the "F" revision which should handle 802.11n. Assuming that all this is true, I'm inclined to buy two of the TP-Link N300 adaptors and figure that sooner or later, the system will grow into them (i.e., I'll get a router with n-capability). If that never happens, no real harm done.
However, just be safe, would the TP-Link N300 adaptor be fully backward compatible with 802.11b/g?
Also, if and when I upgrade either of these computers, I will probably lose the PCI slots. Will these PCI-based adaptors become useless then?
Motherboards are still including the pci slot but as time goes by more of them are droping the slot and going with a x1 Pci-e slot. If you have a Pci-e slot available now it might be a good idea to consider one of those. Another option would be to get a usb wireless adapter and then you wouldn't have to worry about the upgrade.
When you go to buy a wireless adapter it will say that it supports b/g/n so that means it's fully backwards compatible.