Before revision:  The first is a blocked version of column pivoted Householder URLanized as a `` left-looking '' method to minimize the number of write operations (which are more expensive than read operations on a spinning disk drive).
After revision:  The first is a blocked version of column pivoted Householder URLanized as a " left-looking '' method to minimize the number of write operations (which are more expensive than read operations on a spinning disk drive).