3.5Software

Hardware alone cannot do anything on its own. This section covers the fundamentals of software: the OS (operating system) that ties hardware together and makes it usable, the file management mechanisms that organize and store data, and application software—such as everyday spreadsheet tools—that people rely on for daily work.

3.5.1The OS's role and file management

• OS (operating system) is the basic software that sits between hardware and application software, managing the whole computer (Windows, macOS, etc.). Task management assigns CPU time to multiple programs (tasks) in turn, making it appear as though multiple jobs are progressing at the same time.
• Virtual memory uses part of a hard disk or similar storage as an extension of main memory when RAM capacity runs short, making the system appear to have more memory available than it physically does.
• A directory (folder) is a container for classifying and organizing files, and can be nested hierarchically. An absolute path gives the complete route from the top (root) to a target file (e.g., C:\Users\report.txt). A relative path gives the route based on the current location (e.g., ..\report.txt means one level up).
• Backup means making a copy in a separate location in advance, in case data is corrupted or lost. It is a fundamental precaution against data loss from mistakes or hardware failure.

3.5.2Spreadsheet software and OSS

• Spreadsheet software (Excel, etc.) lets you enter values and formulas into cells for aggregation and analysis. Relative reference is the default reference style, where the referenced cell automatically shifts when a formula is copied. Absolute reference fixes a cell with $ (e.g., $A$1), so the referenced cell stays fixed and does not shift when the formula is copied.
• Common spreadsheet functions include SUM (total), AVERAGE (average), and IF (conditional logic). When copying a formula across cells, use an absolute reference when the same cell (e.g., a tax rate) should be referenced from every row, and a relative reference when the reference should shift along with each row.
• OSS (open source software) is software whose source code is published, allowing anyone to obtain, use, modify, and redistribute it free of charge. Besides being free to use, it benefits from many developers contributing improvements—though support may be less extensive than with commercial software.

Consider a salesperson's PC work filing an expense report to see these software elements in action. Powering on the PC starts the OS, and being able to operate several apps at once—expense software, email, a browser—works because the OS's task management finely allocates CPU time to each app in turn. If opening several documents full of images nearly exhausts main memory (RAM), the system keeps running instead of suddenly freezing, thanks to virtual memory using part of the hard disk as an extension of main memory. The finished expense report is organized hierarchically with directories—say, inside a "July" folder within a "FY2026" folder—and when telling a colleague its exact location on the shared server, you use a complete route from the root, an absolute path like \\server\keihi\2026\07\seisan.xlsx; to refer to another file in the same folder, a route based on the current location, a relative path like .\report.xlsx, suffices. Taking a monthly backup onto a separate drive is also essential, in case a file gets overwritten by mistake. When building the expense report in spreadsheet software, copying a formula that computes "transportation cost x tax rate" down each row, you leave the transportation-cost cell as a relative reference (it should shift row by row), but pin the tax-rate cell as an absolute reference (e.g., $B$1), since it should keep pointing to the same cell no matter the row. Leaving the tax-rate cell as a relative reference by mistake is a classic error: as the formula is copied down, the reference shifts along with each row, ending up pointing at the wrong cell. Some business software of this kind is published as OSS and free to use; because its source code is public, the community can improve it and organizations can customize it for their own needs.

3.5.3Section summary

• OS bridges hardware and applications. Task management enables parallel-looking operation; virtual memory extends main memory
• Absolute path = complete route from the root; relative path = based on the current location. Backups keep copies safe
• Relative references shift when a formula is copied; absolute references ($) stay fixed. OSS has published source code and is free to use