From what I recall, in vector machines, operations are still done in parallel due to chaining; the difference is that you're doing e.g. add(v[1]) and mul(v[0]) in parallel, then add(v[2]) and mul(v[1]), and so on, rather than add(v[0]) and add(v[1]) in parallel, then mul(v[0]) and mul(v[1]), &c, which makes support for any vector length trivial.

(I'm sure you know this; this is just for the benefit of anyone else perusing the comment section.)