Yes, up to 512 bits since Skylake. But there are very few real-world tasks that can make use of such wide data paths. One example is media processing, where a 512-bit register could be used to pack 8 64-bit operands and act on all of them simultaneously, because there is usually a steady stream of data to be process using similar operations. In other tasks, where processing patters can’t make use of such batched approaches, the extra bits would essentially be wasted.
Our modern 64 bit processors do use 128 bits for certain vector operations though, don’t they? So there is another aspect apart from address space.
Yes, up to 512 bits since Skylake. But there are very few real-world tasks that can make use of such wide data paths. One example is media processing, where a 512-bit register could be used to pack 8 64-bit operands and act on all of them simultaneously, because there is usually a steady stream of data to be process using similar operations. In other tasks, where processing patters can’t make use of such batched approaches, the extra bits would essentially be wasted.