Describe the technique of packing.
The physical record size will not accurately match the length of the desired logical record and the Logical records may even differ in length. Packing a number of logical records into physical blocks is a common solution to this problem. In UNIX the operating system describes all files to be simply a stream of bytes and in this case the logical record is one byte. The file system automatically unpacks or packs bytes into physical disk blocks say 512 bytes per block as necessary.
The physical size, logical size and the packing technique determine how many logical records are in each physical block. The file perhaps considered being sequence of blocks and all the basic I/O functions operate in terms of blocks.