The Complete Handbook of Computer Software

Chapter 1: Understanding Computer Software

Software is instructions. That distinction — instructions, not objects — is the root of almost everything that makes software different from physical products, and understanding it is the foundation for every decision you'll make about buying, installing, maintaining, and profiting from it.

When you purchase a hammer, you own a physical object. It sits in your toolbox. You can see it, hand it to someone else, and it works the same way for the next person. Software is fundamentally different. When you purchase Microsoft Excel, you are not purchasing an object. You are purchasing the right to execute a set of instructions on your computer. Those instructions tell your processor how to read a spreadsheet file, calculate formulas, and display the result on your screen. You cannot see the instructions directly — they are encoded in binary — but their presence is why Excel does what it does, and their absence is why your computer cannot do what Excel does without them.

This distinction matters immediately in practice. A hammer does not require a license agreement limiting how many people can use it simultaneously. Software almost always does, because each execution of the instructions consumes computing resources — memory, processor cycles, disk space — that must be allocated and metered. A hammer does not require security patches when vulnerabilities are discovered in how hammers work. Software requires them constantly, because the instructions that make it useful can also be exploited by attackers if they contain