A technique is provided for storing updated values of a data item in a segment of memory in which stored values cannot be individually overwritten, such as a flash memory. Each updated value is stored at an address which has space for a far pointer and a local pointer. When a new value is stored, the local pointer of the previous value is set to point to the address of the new value. When a chain of nodes of this type has been established and a further update value is to be stored, it is entered at a new node and a far pointer at a much earlier node of the chain is set to point to the new node so that the most recent value can be found without having to follow the local pointers in all of the previous nodes.