Programs

In practical conditions, a computer program might include anywhere from a dozen instructions to many millions of instructions for something like a word processor or a net browser. A typical current computer can execute billions of instructions every second and almost never make a mistake over years of operation.
Large computer programs may take teams of computer programmer’s years to write and the prospect of the entire program having been written completely in the manner planned is unlikely. Errors in computer programs are called bugs. Sometimes bugs are caring and do not affect the usefulness of the program, in other cases they might cause the program to completely be unsuccessful in yet other cases there may be subtle problems. Bugs are usually not the fault of the computer. Since computers just execute the instructions they are given, bugs are nearly always the result of programmer error or a mistake made in the program's design. In most computers, individual instructions are stored as machine code with each instruction being given a unique number. The command to add two numbers jointly would have one opcode; the command to multiply them would have a different opcode and so on.