A small piece of dATA inserted in order to achieve a desired memory alignment or other addressing property. For example, the PDP-11Unixlinker, in split I&D (instructions and dATA) mode, inserts a two-byte shim at location 0 in dATA space so that no dATA object will have an address of 0 (and be confused with the C null pointer). See also loose bytes. [Jargon File] (1994-12-21)