analysis on character content (see Screen scrape) and convert the message to/from the desired graphical form, depending on its context. Being a specialized purpose operating system, TPF does not host a compiler/assembler, text editor, nor implement the concept of a desktop as one might expect to find in a general-purpose operating system. TPF application source code is commonly stored in external systems, and likewise built "offline". Starting with z/TPF 1.1, Linux is the supported build platform; executable programs intended for z/TPF operation must observe the ELF format for s390x-ibm-linux. Using TPF requires a knowledge of its Command Guide since there is no support for an online command "directory" or "man"/help facility to which users might be accustomed. Commands created and shipped by IBM for the system administration of TPF are called "functional messages"—commonly referred to as "Z-messages", as they are all prefixed with the letter "Z". Other letters are reserved so that customers may write their own commands. TPF implements debugging in a distributed client-server mode, which is necessary because of the system's headless, multi-processing nature: pausing the entire system in order to trap a single task would be highly counterproductive. Debugger packages have been developed by third party vendors who took very different approaches to the "break/continue" operations required at the TPF host, implementing unique communications protocols used in traffic between the human developer running the debugger client and the server-side debug controller, as well as the form and function of debugger program operations at the client side. Two examples of third party debugger packages are Step by Step Trace from Bedford Associates and CMSTPF, TPF/GI, and zTPFGI, all from TPF Software, Inc. Neither package is wholly compatible with the other, nor with IBM's own offering. IBM's debugging client offering is packaged in an IDE called IBM TPF Toolkit. What TPF is TPF is highly optimized to permit messages from the supported network to either be switched out to another location, routed to an application (specific set of programs) or to permit extremely efficient accesses to database records. Data records Historically, all data on the TPF system had to fit in fixed record (and memory block) sizes of 381, 1055 and 4K bytes. This was due in part to the physical record sizes of blocks located on DASD. Much overhead was saved by freeing up any part of the operating system from breaking large data entities into smaller ones