PATCH OR REVISE SOFTWARE

index (DCI) with error stop and recommended corrective measures: Replace pcbs in locations 4C28-4C30. PATCH OR REVISE SOFTWARE.— Mainframes also have the option to allow you to manually insert and make revisions of machine code or insert revisions using external peripheral devices. Patches or revisions to the software are written by authorized personnel only. The patches or revisions are entered using inspect and change routines or equivalents using the controls, data entry, and data display man/machine interface. SUMMARY—COMPUTER INSTRUCTIONS AND MAN/MACHINE INTERFACES In this chapter we introduced you to computer instructions and to ways you can interface with a computer. The following information summarizes important points you should have learned: COMPUTER INSTRUCTIONS— Computer instructions are commands to the computer to tell the equipment to perform a designated operation. The instructions are processed by the central processing unit. PROGRAMS.— Programs are sequences of instructions written for various purposes to solve problems or types of problems on a computer, to manage the computer’s own resources and operations, and/or to maintain computers. LEVELS OF INSTRUCTIONS.— Instructions may be either microinstruction or macroinstructions (a predetermined set of microinstruction). INSTRUCTION TYPES.— Instructions may be classified by what they do, their operation. They may also be classified by their action on an operand-read, store, or replace. INSTRUCTION SIZES.— Instruction sizes vary depending on the instruction and the computer. INSTRUCTION FORMATS.— Every instruc- tion has an operation (op) code to tell the computer what to do. It may also have an operand to give the address of the data to be operated on or to give other fields or designators. INTERFACING WITH COMPUTERS.— The man/machine interfaces enable operators/technicians to control the computer’s operation. These include control panels and operator panels/consoles. MAN/MACHINE OPERATING MODES.— Computers can be operated in a variety of modes. This is very helpful when you are troubleshooting. Run mode continually executes instructions one after another. Stop mode causes the computer to stop; it will not restart until directed by some operator action. Step mode enables you to have the computer execute one instruction at a time so you can test the contents of computer registers and memory locations to verify correct operation or identify a problem. MAN/MACHINE INTERFACE OPERA- TIONS.— Many operations can be accomplished by providing information to the computer through an interface. MAN/MACHINE INTERFACE FUNC- TIONS.— Many general functions can be performed through an interface. It is up to you to learn all you can about how the computer systems you work with process instructions and what capabilities are available to you through man/machine interfaces. This will enable you to interpret computer instructions and interface with the computer to diagnose and isolate problems. 8-26