that allocate file space in clusters another example of sacrificing space to internal fragmentation so as to simplify memory management is the buddy method described later in this section the process of searching the memory pool for block large enough to service the requestpossibly reserving the remaining space as free blockis referred to as sequential fit method sequential-fit methods sequential-fit methods attempt to find "goodblock to service storage request the three sequential-fit methods described here assume that the free blocks are organized into doubly linked listas illustrated by figure there are two basic approaches to implementing the freelist the simpler approach is to store the freelist separately from the memory pool in other wordsa simple linked-list implementation such as described in can be usedwhere each node of the linked list contains pointer to single free block in the memory pool this is fine if there is space available for the linked list itselfseparate from the memory pool the second approach to storing the freelist is more complicated but saves space because the free space is freeit can be used by the memory manager to help it do its jobthat isthe memory manager temporarily "borrowsspace within the free blocks to maintain its doubly linked list to do soeach unallocated block must be large enough to hold these pointers in additionit is usually worthwhile to let the memory manager add few bytes of space to each reserved block for its own purposes in other wordsa request for bytes of space might result in slightly more than bytes being allocated by the memory managerwith the extra bytes used by the memory manager itself rather than the requester we will assume that all memory blocks are organized as shown in figure with space for tags and linked list pointers herefree and reserved blocks are distinguished by tag bit at both the beginning and the end of the blockfor reasons that will be explained in additionboth free and reserved blocks have size indicator immediately after the tag bit at the beginning of the block to indicate how large the block is free blocks have second size indicator immediately preceding the tag bit at the end of the block finallyfree blocks have left and right pointers to their neighbors in the free block list the information fields associated with each block permit the memory manager to allocate and deallocate blocks as needed when request comes in for words of storagethe memory manager searches the linked list of free blocks until it finds "suitableblock for allocation how it determines which block is suitable will