Cutom built PC

Go into a shop and look at ready built / package.
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1. You can listen to it and see what noise it gives off
2. You know what you're getting and if you have a problem with it, the whole thing is supported by 1 company. If you go for components, you rely on each component warranty or the shop that built it.
3. All the components will match, so you're far less likely to have one that is out of step with the others, thereby causing a bottleneck and slowing the whole system down.
4. Put your old disks in an external disk housing.
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If you were a geek, the advice could be different, but then a proper geek wouldn't use this forum to ask this sort of question and would have been rather more technical.