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I was tinkering with my PC yesterday and now I'm wondering about these things. Not that it really matters to me, I'm just curious.

Example below:

notches

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@jnovacho Start and reset are probably pretty self-explanatory. I'm not sure about the lock and the other though. I'd be interested to know as well –  Cruncher Dec 6 '13 at 14:19
    
One of them is OC –  Journeyman Geek Dec 6 '13 at 14:29
    
silkscreened on the board next to the lock is "core unlocker". My guess would be that it is either to try and use the 4th core on a 3 core cpu (AMD only) or to remove limits on how high the CPU can be overclocked (going from generally safe limits, to values that need sub-ambient cooling of the sort normally only used for competitive overclocking.) Unfortunately glare is obscuring most of the name on the board and Asus uses Formula branding in a number of high end models. –  Dan Neely Dec 6 '13 at 20:54
    
@jnovacho, looks like it could be this motherboard, but only OP would know for sure –  Sean Cheshire Dec 6 '13 at 21:33
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This question appears to be off-topic because it is a "guessing-game" type question. See meta.superuser.com/a/6074/23133 –  Ƭᴇcʜιᴇ007 Jan 31 '14 at 21:13

2 Answers 2

up vote 27 down vote accepted

After quite a bit of search i found this paragraph in a document called PCI Express™ Card Electromechanical Specification Revision 1.1 :

As shown in Figure 5-1, a ridge feature is defined on the top of the connector housing on one side. This feature can be used to facilitate card retention. A retention clip may be mounted on 15 an add-in card and latched on the ridge.

As seen here enter image description here

And shown here (from version 1.0 of the spec)

enter image description here

Also found the following pattent http://www.google.com/patents/US7850475

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It says in reference to the notches on the ridge "frequency and location at supplier discretion. ridge may be continuous with no breaks" in note (5) so the ridge has to be there but the notches don't. –  Brian Dec 6 '13 at 12:22
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Interresting... Never noticed that ridge myself, but it is there on all PCIe motherboards I have currently lying around. I have never seen anything using that clip mechanism though. With a screw or retaining clip on the bracket usually a PCIe card sits well enough in the slot, but it could have some wiggle room on the other end. Might be of use in a heavy vibration environment, but I have never seen such clips. Nor have I seen any cards with the mounting hole for such a clip. –  Tonny Dec 6 '13 at 15:37

Some slots have them, others don't.
Seems to depend on where the motherboard manufacturer bought them from.

As far as I know the only reason for them is to slightly weaken the mechanical stiffness of the plastic.
This makes it a bit easier to push a card in the slot without having to exert extreme force and possibly bend the motherboard while doing it.

Is someone knows of another reason I'm very interested to hear it too.
(Nice question !)

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