A high-strength and high-toughness ferritic steel having a tensile strength of not less than 1,000 MPA and a Charpy impact value of not less than 1 MJm2 is provided. This system is versatile in that it can be used on buttons with one or up to four holes. Additionally, if no mutator operation will occur before a collection set of one or more cars will be collected, any reference located outside that collection set but referring to an object within the collection set is not recorded in a remembered set but is recorded instead in a scratch-pad list of entries that identify references to collection-set objects that need to be evacuated.