Editing ATX (section)

== Connectors ==
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[[File:Several atx io shields (smial).jpg|thumb|ATX I/O plates for motherboard rear connectors]]

On the back of the computer case, some major changes were made to the AT standard. Originally AT style cases had only a [[computer keyboard|keyboard]] connector and expansion slots for add-on card backplates. Any other onboard interfaces (such as [[serial port|serial]] and [[parallel port]]s) had to be connected via [[Ribbon cable|flying leads]] to connectors which were mounted either on spaces provided by the case or brackets placed in unused expansion slot positions.<ref>{{Cite news |author1=Alex Campbell |date=2016-07-26 |title=A brief history of PC case design |language=en |work=PC Gamer |url=https://www.pcgamer.com/a-brief-history-of-pc-case-design/ |access-date=2023-12-09}}</ref>

ATX allowed each motherboard manufacturer to put these ports in a rectangular area on the back of the system with an arrangement they could define themselves, though a number of general patterns depending on what ports the motherboard offers have been followed by most manufacturers. Cases are usually fitted with a snap-out panel, also known as an I/O plate or I/O shield, in one of the common arrangements. I/O plates are usually included with retail motherboards to allow installation in any suitable case. The computer will operate correctly without a plate fitted, although there will be open gaps in the case which may compromise the EMI/RFI screening and allow ingress of dirt and random foreign bodies. Panels were made that allowed fitting an AT motherboard in an ATX case. Some ATX motherboards come with an integrated I/O plate.

ATX also made the [[PS/2 port|PS/2-style]] [[mini-DIN]] keyboard and mouse connectors ubiquitous. AT systems used a 5-pin [[DIN connector]] for the keyboard and were generally used with serial port mice (although PS/2 mouse ports were also found on some systems). Many modern motherboards are phasing out the PS/2-style keyboard and mouse connectors in favor of the more modern [[USB|Universal Serial Bus]]. Other legacy connectors that are slowly being phased out of modern ATX motherboards include 25-pin [[parallel port]]s and 9-pin [[RS-232]] [[serial port]]s. In their place are onboard peripheral ports such as [[Ethernet]], [[IEEE 1394|FireWire]], [[eSATA]], [[sound card|audio ports]] (both analog and [[S/PDIF]]), video (analog [[D-sub]], [[Digital Visual Interface|DVI]], [[HDMI]], or [[DisplayPort]]), extra [[USB]] ports, and Wi-Fi.

A notable issue with the ATX specification was that it was last revised when power supplies were normally placed at the top of many old computer cases rather than at the bottom, as with many modern computer cases. This has led to some problematic standard locations for ports, in particular the 4/8 pin CPU power, which is normally located along the top edge of the board, convenient for top-mounted power supplies. This makes it very difficult for cables from bottom-mounted power supplies to reach, and commonly requires a special cutout in the back plane for the cable to come in from behind and bend around the board, making insertion and wire management very difficult. Many power supply cables barely or fail to reach, or are too stiff to make the bend, and extensions are sometimes required due to this placement. Modern power supplies often have longer cables to alleviate this issue.