Just wondering if I can utilize my old PCs to start mining cryptos. But not sure where to start for those old types of equipment. Need advice.
Here is some small information about the equipment I have in my storeroom:
What I'm looking for? Which GPU should I buy for each PC? I mean which one will support with them. Also, you can suggest any CPU mining coin.

1. Quad-core 2.9, Intel G41 mainboard, 8 GB RAM, 1 GB internal graphics
Which GPU best suits this one for mining? (if any)

2. Core 2 Duo, Intel G31 mainboard, 4GB RAM, 1 shared graphics
Which GPU best suits this one for mining? (if any)

3. Core i5-650, H-55 mainboard, 4GB RAM, 1 GB onboard graphics
Which GPU best suits this one for mining? (if any)


Thanks in advance for your valuable time.