It costs $10-$40 to buy a real router that will last at least a few years.
It costs about 350 or more hours of time and maintenance to build your own router and maintain it using an old pentium 100 box. It costs you plenty more electricity to use an old pentium box too. Why do dorks do this? build there own router and go on the internet bragging about how they are using an old AT or ATX case? They think they are pretty smart and uber don't they?
It is more of a fire hazard to use an old computer as a router.
It costs more money. If you build routers out of old computers, and you use network cards to make your own ports, you are not cool. You are a dork.
After adding up the electricity cost over a couple months, your home made router will cost you plenty more than the AC adapter based hardware router.
The only way to build your own efficient router is to own a router company. Stop building stupid useless routers when you can buy one for $20 and save $1500.00 in maintenance, electricity, and stress costs.
Also, some old PC (or heck even a new one) is going to have fan noise. Fan noise is stressful, loud, and a waste of electricity.
Building your own router is an academic exercise for folks like University professors and is not economical in the real world.
If you for some reason really do need that router with software you can control, then at least use something reasonable like a router which you can change the software on (upload the O/S to the chip). Many Linksys routers and others allow you to change the software and kernel embedded on the chip.
Even a small tablet or laptop computer with plenty of PCMCIA slots will still cost more electricity to run than a router with an AC adapter.
Using a custom home brewed router built from a PC or laptops is just dumb.
For a large server company where one thinks buying thousands of routers would be more expensive than rolling your own: once again, please study electricity costs.. the electricity costs of using old AT/ATX cases and PC's for routers will quickly add up.
I've never built my own router out of an old AT or ATX case because I noted how much wattage a router runs at, versus an AT/ATX PC running idle. It took me about 14 seconds to decide whether or not using an old computer as a router was worth it. Computers use 15-80 watts just sitting there doing nothing. Routers with ac adapters don't.
For some reason, many dorks (maybe those people who live in Apartments or university dorms where they care less about electricity since someone else pays the bill) think that building AT/ATX routers is cool and shows signs of elite skillz and intelligence. Yep they "threw linux on an old pentium 100 and make use of the old PC" (wasting some network cards too). These dorks think they are saving money since they are using old computers and network cards. All they think about is what they saved in recycling computers, but not how much they lost in electricity and fan noise.
Fire? What chances are there an AT/ATX case would catch on fire, you are thinking? Well yes, old computers do catch fire in server rooms, it happens. And yes a ATX/AT cases are more prone to fire than a simple router without any complex circuits, fans hot CPU, etc. Why? The old ATX/AT cases have several fans in them that are not needed for routing which could fail. Power supply fan, CPU fan, and some even have case fans or graphics fans! Worn fans and hotter jack of all trade CPU's in ATX/AT cases are more of a risk and a waste of electricity money.
In fact these "built my own router" dorks need to do thinking. That's all it takes, just think and calculate up front! Participate in intelligent and critical analysis before building a square wheel. Why do people not consider electricity costs and annoying fan noise before building these AT/ATX routers?
These dorks even go as far as building special server rooms or closets in their homes so that they can muffle the noise out. That costs them thousands of dollars in renovations. But boy did they save money, by not buying a $15 router with an AC adapter!
It's just "pargence" showing its face once again.