ATX? BTX?

I'm told that ATX = 20-pin PSU and BTX = 24-pin PSU.  True?  Or untrue?  Or... there's more to it?

Also, is 20-pin generally seen as old and outdated?

There is more to it.

I don't know shit about BTX

There are several kinds of ATX. 20-pin, 20-pin w/+12v, 20+4-pin with +12v (the 20+4 is a 20-pin with a removable extention that turns it into a 24-pin), the 24 pin (always has +12v, cannot be used as a 20-pin), 20+4 or 24-pin w/6-pin PCI-Express, and 20+4 or 24-pin w/8-pin board power (instead of 4-pin +12v) for server motherboards.

BTX is a failed form factor so that Intel could cool its chips. The power supply connectors are the same.

So I shouldn't get BTX unless I have an Intel processor.  Which I do.  (P4)  Should I go for BTX over ATX, then?

stop thinking about btx and just go atx like everyone else

>>4
ATX and BTX are both motherboard form factors, neither of which limit you to a single socket/processor type. Get an ATX motherboard that supports the type of socket your processor uses (Pentium 4 processors are typically either on LGA775 or S478), BTX is widely considered a failure and goes practically unsupported.

BTX is the mirror of ATX  - the same except reversed for mounting components.  A lot of 'workstaion' type PCs are sold with this configuration (eg. the Dell Optiplex GX range are BTX form factor)

BTX is really the shit.

Yeah we have a few Optiplex BTX machines. It's a really nice form factor if you can get it. That is if you can and it's cheap. Otherwise plain ATX is just fine.