This episode is about the ATX size format
Its been a very difficult episode to do as i wanted to keep it simple, although there's so much information to go through
ATX (Advanced Technology Extended) is generally related to the motherboard and power supply physical size
It was patented by David Dent in 1995 at Intel and was based on the older AT sized motherboards 

Generally ATX is heard to relate to the power supply size format however actually relates to both the dimensions of the motherboard and the power supply carrier inside a PC case
The goal was to standardize component size and fixings, allowing manufactures to create computer cases to a standard
Some cases had there own bespoke sized power supply's but still allowed an ATX sized motherboard

The ATX standard controls the power supply rear hole size and fixing methods as well as the motherboard size and its fixing screw locations,
It also controlled the power connector design to the motherboard as well  as the input / output port hole size and location on the rear of the computer case

ATX motherboards are slight smaller than the original AT therefore most cases will not carry an older AT motherboard
ATX is a standard and covers many other sized motherboards including microATX, FlexATX, Nano ITX and mini ITX, all being able to fit in to an ATX case
As if feb 2022 ATX standard is now at revision 3 and is still in use today

EATX was around the same time, and is a much larger version to carry dual CPUs and was 13 x 12 inches compaired to ATX 9.6 9.6 inches
EATX cases generally would carry an ATX motherboard as the screw fixing locations are in the same positions
EATX power supply's generally were alot larger being they had to power 2 CPUs thus could be with a normal ATX motherboard
by using only 1 of the CPU power connections

Video Graphics cards that required power generally could use the second unused CPU power connector of the EATX power supply when used with a small 4 to 6 or 8 pin video graphics card adapter cable

2004 Intel introduce BTX (Balanced Technology Extended) format, it was mostly the motherboard reversed in the case and was short lived with 
Intel discontinuing development in 2006

The rear hole used for the in / out connectors was a standard size and location, the actual position of those connections depended on the manufacture
and thus required the use of the manufacture specific cover plate that fitted in the ATX case

I have built many PCs over the years and seen small changes with some ATX components
such as the power supplies had a 100mm fan inside pushing air over the components then out the rear
the same fan was then moved to the outside pulling air over the components
then was changed to a larger 120mm fan inside, downwards thus pulling air out directly away from the motherboard

Same power supply manufacture tried to push the depth limit with large 1kw outputs however normally resulted in the top bay of the case being
unuseable as the power supply was to long restricting access to be able to cable the top bay.

Motherboard power connectors were generally at the top, as this was the location of the power supply, a few manufactures moved the power supply
to the base of the case creating issues with power cable length not being long enough to reach the top of the motherboard.

Today most PCs are tiny and manufactures have mostly abandoned the use of the ATX size standards
gone are the days where you could swap any power supply as now they are bepoke made parts for that computer case and motherboard power connections

As the case, motherboard and power supply are all bespoke designed parts, almost all PC's purchased today do not adhere to the ATX standard unless self built.

ATX was mostly a consumer PC parts sizing, servers were always bespoke designs.  Although some cross overs happened
such as the FLEX 1U power supplies in the small 1U server cases.