Confusion on reading specs for PCIe slots

[danieldevaney2290]

Hello, I am looking to expand my system memory. I know enough of the jargon to know what I am doing and how to install but when I look at my motherboards PCIe slot descriptions and a few of them I don't understand fully. Could I have someone help me out

Here are the descriptions that allude me
2 x PCIe 2.0 x16 (x16 or dual x8)
1 x PCIe 2.0 x16 (x4 mode, black)

It's the part in the description that is in parenthesis that I don't understand

 

[rolli59]

First one says that you have two X16 version 2.0 slots, when running one of them it will run at X16 but if running both in SLI or Crossfire they share bandwidth and run in X8 X8.
The PCIe X16 slot is limited to X4 speed in the second parentheses although physically it will accept a X16 card (connector)

 

[Dereck47]

System memory has nothing to do with PCIe slots. System memory is installed on DIMM slots on your motherboard.

PCIe slots are used to connect various types of expansion cards. Examples are Graphics Cards, Sound Cards, RAID Controller cards, etc. There are many different things you can connect to a motherboard via a PCIe slot.

This quote is from Wikipedia:

Lane

A lane is composed of a transmit and receive pair of differential lines. Each lane is composed of 4 wires or signal paths, meaning conceptually, each lane is a full-duplex byte stream, transporting data packets in 8 bit 'byte' format, between endpoints of a link, in both directions simultaneously. Physical PCIe slots may contain from one to thirty-two lanes, in powers of two (1, 2, 4, 8, 16 and 32). Lane counts are written with an x prefix (e.g., x16 represents a sixteen-lane card or slot), with x16 being the largest size in common use.

2 x PCIe 2.0 x16 (x16 or dual x8)

The part in parenthesis means that the 2 slots share resources with the motherboard chipset. For example, if you have 1 Graphics card connected it will operate at full speed using all 16 lanes (x16). If you have two (Dual) Graphics cards in SLI or CrossfireX each card will operate using 8 lanes (x8).

It doesn’t necessarily have to be 2 Graphics cards. If you have a Sound card connected to a slot that’s shared with your Graphics card, that also will reduce your graphics processing ability to x8.