Given two computers:

  1. Has X gigabytes of RAM, that's the amount it ships with and that's all it will ever have, it can be designed around that number in whatever way is most efficient, solder chips directly to the motherboard if that turns out to save money, whatever.

  2. Has X gigabytes of RAM, but field upgradable to 4X gigabytes.

How much does the expandability cost? That is, not the cost of buying the extra RAM at expansion time, but just to include the capability on the motherboard, how much does that add to the initial cost of the machine?

Does it have any effect on performance? If memory wasn't going to be expandable, could you shave cycles off memory access time or anything?

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    \$\begingroup\$ Whatever the slots are worth, which is probably tens of cents to a dollar or two per slot depending on what quantity they are buying them in. Then the time it takes them to integrate them into the design. It has a small effect on performance because there is more capacitance. No, probably not. \$\endgroup\$ – Voltage Spike May 2 '17 at 15:45

You add the cost of:

  • Connectors
  • The actuall RAM module that might be more expensive than the individual components
  • The fact that if you use a connector, someone will have to manually insert the modules, as I don't think this can be done by machine (in contrast to placing the components directly on the motherboard, as you would do when you don't use modules).

Finally, there is also the fact that you are increasing thickness - one of the main reasons laptop manufacturers are going for on-motherboard RAM. You can't get the thin formfactor of a few millimeters when you have a (in relative terms) thick fat connector for your ram modules.

There might be a few more reasons, but this is what I could come up with now.

I don't think there should be any impact on performance. The standards and specs are built to be able to go over connectors - they don't go any faster by ommiting them. On top of this the performance gain by increasing RAM speed is not very significant - that's what the registers, L1, L2, L3 ... caches are there for.


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