Raspberry Pi

There is some good information in this thread, some bad information and some "sage" information. The "sage" is probably what the OP needs to know. You can realistically drive around 50 erupters from a raspberry pi.

There are two theoretical limitations. The first is the number of addressable units and the second is the maximum number of hops in a chain. Properly accounting for both of these requires you to realize that most hubs out there are built with 4 port chips. A 7 port hub is really two x 4 port hubs chained internally. A 10 port hub is really three x 4 port hubs chained internally as a tree.

Each of these 4 port hub chips is addressable and takes up one of the 127 available addresses. This in practice reduces the number of devices from 127 to around 90. Not that this is an issue for a raspberry pi, but it is worth understanding.

More importantly, this topology means that two of the ports on a 10 port hub are one "hop" away from the input, the other 8 are two "hops" away. Hence someone taking three, 10 port hubs and daisy chaining them as previously recommended may find themselves wondering why only two of the 10 work on the last hub but someone else who got lucky and plugged into a 1 hop port instead of a 2 hop port found it working.

All of this smoke and mirrors and voodo magic can be avoided by connecting your hubs as a "tree" instead of a "chain".

Finally, it is worth revisiting the "sage" wisdom. Do you want to know why 49 is a magical number?

It is what you get when you plug a 7 port hub into a computer then plug 7 more 7 port hubs into it. There are 49 usable ports on the leaf nodes which are between 2 and 4 "hops" away from the root. You are using 65 of the 127 USB addresses, 49 for the mining device and 16 for the hub devices.

49 is also right at the limit of what a raspberry pi can manage.

Now, as an exercise for the interested reader ... can you plug a 10 port hub into a pi and plug 10 x 10 port hubs into it? Looking at from a "hop" point of view each of the leaf nodes are still between 2 and 4 "hops" away from the root. And, if you only consider leaf nodes, there are 100 devices and 127 addresses. It should work, right?

Nope. You need to give each of the 4 port building blocks an address and there are 33 of them, three per 10 port hub. You are trying to address 133 devices with 127 addresses.

So, the theoretical answer ignoring generally available hardware is 127 devices. The practical answer using commonly available hardware is 92 devices and a realistic answer considering the capabilities of the raspberry pi is around 50 devices.

Divide by 10 to get the number of 10 port hubs.