If computation is instantaneous, then you could recurse down to a single pointer, which points to a pair of pointers, which each point to another pair, and so o

If computation is instantaneous, then you could recurse down to a single pointer, which points to a pair of pointers, which each point to another pair, and so on until you have an arbitrary amount of your data. Since computation is instantaneous, it is instantaneous to compute this first pointer for the contents of any hard disk. And since computation is instantaneous, rebuilding the files on the disk from that pointer is instantaneous. Your compression ratio would approach infinity.