Not really, the vast majority of computers ever built had only one CPU (i.e. core) and thus functioned perfectly well without a multicore processor.
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Parallel
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Solder comes in 2 basic varieties, solid and rosin-core. Simple rosin-core solder is a tube of low-melting-point metal with flux filling the single core down the center. Multicore solder has multiple hollows in it, each filled with flux.