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When computers were first developed, they were thought of as calculating machines. Early computers performed such tasks as calculating ballistic tables for artillery shells. However, when adapted by industry, they were used for storing and retrieving numeric and non-numeric information. The largest computer customers were banks, insurance companies, and government agencies.
Early computers had no operating systems, and the user interfaces were primitive. An example in the early days of personal computers was the Altair 8800. The user interface was a panel of toggle switches and light-emitting diodes (LEDs). Programmers had to be intimately familiar with the computer they were programming. Computers using the same microprocessor but developed by different companies worked with the same command set, but the programmer had to be familiar with entirely different hardware. Operating systems were developed as a go-between from the programmer to the hardware. Completely different computers using the same operating system were nearly identical to the programmer.
Every operating system comes with a user interface that is so closely associated with the operating system that the two are usually thought of as one and the same. However, they are separate entities, and with Unix and Linux, the end user can choose from different user interfaces. Developers of user interfaces, from the start, used familiar metaphors to represent the computer.
The metaphor used to represent mass storage is a filing cabinet. That filing cabinet is a hard disk, a solid-state drive (SSD), an SD card, or any of the many mass storage devices described in the hardware class. When a collection of data, such as a word processor document, a spreadsheet, or a map, is stored in the filing cabinet when not in use. The filing cabinet has one or more drawers. These are represented as the C drive, the D drive, etc. Therefore, consider each drive letter as a drawer in the filing cabinet.
Each drawer in the filing cabinet holds at least one file folder. This can be one huge folder called the root folder. Most often, the root folder contains other folders. Any folder can contain other folders. How the folders are organized is up to the end user. Folders also contain the files that computers work with.
In some contexts, folders are called directories. This is just a different name for the same thing. The philosophy behind this is that when you open a folder, you see a directory of files and other folders contained in that folder. Therefore, the terms folder and directory are interchangeable.
Files are the working documents. They can be word processor documents, spreadsheets, pictures, web pages, or any other collection of data that a computer works with. When you open a folder, you see a directory of files and other folders in that folder.
In many contexts, a file is called a document. Like folder and directory, file and document mean the same thing.
When you open a file, the data is moved to the computer's memory. This is separate from the mass storage above. The workspace is the random-access memory (RAM) that the microprocessor works with directly. While the file is in memory, it is no longer safely on the hard disc, SSD, etc., and any changes will be lost if the computer is turned off. Files must be safely saved to the hard drive (filing cabinet) before turning off the computer.
Imagine that when you open a document, you make a copy and put it on your desk to work with it. While it is on your desk, the original is safely in the filing cabinet. When finished, remove the original from the filing cabinet, discard it, and replace it with the new file. Once the file is in the cabinet, it is safe. However, if you leave your working copy on your desk, it can be stolen, accidentally thrown away, or blown out the window. When you are working on a file, it is in the computer's memory and is vulnerable to accidental loss. Therefore, you should save your work frequently, keeping the safe copy on the hard disk up to date.
The above is a general overview and doesn't cover all the technology that makes a computer appear much simpler than it is. Let's now briefly review the hardware that makes it all happen. If you are taking the entire information technology course, you should have already studied the following topics in detail during the computer hardware class.
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