It is unusable because it is in blocks too small to be requested. Caused by over-allocation. First fit reservation - Search the free list for the first block big enough for the request. Split it if necessary, allocating part and putting the remainder back on the free list. A handle is an intermediate reference to a reserved block.
Application programs can only refer to handles whose locations never change.
The values of the handles are pointers to the reserved blocks. Liberation with a Sorted Free List Free list is kept in order of increasing RAM addresses. Liberation requires a search of the free list to put the liberated block in sorted order. Boundary Tags Eliminates the need to search the free list. If it is free, it also has its size at both boundaries and two links at the left boundary linking it into a doubly linked free list.