Noobie Question - What are the sizes of ATX I can fit in my case?

[tarabender8]

I bought a pre-built from HP in 2009 (I know, i'm sorry), It is the HP Pavillion p6210f and the case size on the website says its a mid ATX case. Does this mean it will support all types of ATX motherboards, or just some, and if so, which ones?

Here is the specs for the PC - https://support.hp.com/us-en/product/hp-pavilion-p6200-desktop-pc-series/3999459/model/4006883/document/c01852858

I have also upgrades the PSU, Ram, GPU, and HDD.

 

[Calvin7]

It supports Micro-ATX motherboards.

Retail boxed motherboards do not use the HP front panel connector. The case is very basic with very little cooling. I would recommend buying an inexpensive bare PC case with room for more fans.

https://www.newegg.com/Computer-Cases/SubCategory/ID-7?Tid=7583&Order=PRICE

 

[R0GG]

Your desktop is described on HP support page as mid-size ATX but n other website it is described as a Mini-Tower (would not fit full ATX motherboard)
On the other hand from pictures of your desktop maintenance manual it doesn't seem to be able to fit a full ATX motherboard (there is no room for expansion vertically as the installed Micro-ATX motherboard seems to come very close to the power supply

you can go for a Micro ATX motherboards (same Form Factor as the one installed in your PC) or the smaller Mini ITX) which latest iterations come packed with most full ATX motherboards features..

HP Pavilion P6210F Mini Tower System >> http://www.stuartconnections.com/en/systems-with-cpu/345-HP-Pavilion-P6210F-Mini-Tower-System-Athlon-II-X4-26GHz-6GB-Ram.html