CompTIA Tech+ (FC0-U71): Operating Systems, File Systems and File Management

The operating system is the middle layer between applications and hardware: applications ask the OS for what they need (open a file, play a sound, draw a window, send data over the network), and the OS does the hardware-specific work. This makes software portable: a program built for an OS works across the wide range of hardware that OS supports, because the OS — through each device's driver — hides the differences between one manufacturer's component and another's.

The OS is not the first software to run. When a computer powers on, the firmware on the motherboard (BIOS or UEFI) tests the hardware (the power-on self-test) and then hands control to the OS loader. From then on the OS is in charge of the hardware, and applications reach the hardware only through the OS. Applications such as word processors and browsers run on top of the OS; they are not part of it.

An OS performs five management jobs named in the objectives, and each one answers a different question. When a scenario describes something the OS is doing, identify which question it answers.

Two pairs are easy to confuse. Application management deals with programs as installed software (install, update, uninstall); process management deals with programs while they are running (sharing the CPU and memory). Device management controls hardware; access control controls people — requiring an administrator password before new software can be installed is access control.

Operating systems come in four types, and the right one depends on the device and on who it serves. A mobile OS (Android, iOS, iPadOS) runs smartphones and tablets for one user, with touch input, an app store and strong battery management. A desktop/workstation OS (Windows, macOS, desktop Linux distributions, ChromeOS) is a general-purpose system for one person at a computer running many applications. A server OS (Windows Server, server Linux distributions) provides shared resources — files, user accounts and sign-ins, websites, databases, email — to many clients over a network, and is built for reliability and remote management. An embedded OS is built into a dedicated device to run one fixed set of functions on limited hardware: thermostats, appliance control panels, printers, routers, cameras, car systems and medical devices.

The deciding questions are how many people the system serves (one, or many over a network) and whether it is a general platform for installable apps or runs a fixed job on a dedicated device. Users rarely interact with an embedded OS directly and usually cannot install their own apps on it.

An OS offers two kinds of interface: a command-line interface (CLI), where you type text commands at a console, and a graphical user interface (GUI), where you use windows, icons, menus and a pointer or touch. Examples of command lines are Windows Command Prompt and PowerShell, and the Terminal on macOS and Linux (running a shell such as bash or zsh). The GUI is the desktop you click through — File Explorer, Finder, the Settings app.

Many servers are installed without a desktop environment to save resources and reduce what can be attacked. On such a server there is no graphical desktop to work in, so the administrator manages it from the console or a remote command line; a remote session, if one is allowed, simply opens a command prompt rather than a desktop.

A file system is the method an OS uses to organise and track files on a storage volume, and you choose one when you format a drive; the choice decides which features you get and which operating systems can use the drive. The five to know, plus the older Mac format they are often compared with:

Choose by asking two things: which operating systems and devices must read and write the drive, and which features or file sizes it needs. Both Mac file systems, APFS and the older HFS Plus, are poor choices for a drive that must also work on Windows PCs. A drive used by only one OS can take that OS's native file system and its features — a Linux server's data disk is normally ext4. A drive that moves between different systems needs a format every one of them supports, and the FAT32 4 GB per-file limit matters whenever single files such as videos or disk images are large. A camera's memory card, for example, is formatted FAT32 or exFAT, whichever the camera accepts.

File management is organising, finding, copying, moving, renaming and deleting files, and folders (directories) are the containers that make it possible. Folders nest inside other folders to form a tree that starts at the root of a drive. A file's path describes its location in that tree: on Windows a path starts with a drive letter and uses backslashes (C:\Users\Sam\Documents\report.docx); on macOS and Linux paths start at / and use forward slashes (/Users/sam/Documents/report.docx). File Explorer (Windows) and Finder (macOS) are the GUI file managers; the command line does the same jobs with commands.

• Copy creates a second, independent file; the original stays where it was.
• Move relocates the file; it no longer exists in the old location. Cut and paste is a move.
• Rename changes the name (and, if you change the extension, how the OS treats the file).
• Delete usually sends the file to the Recycle Bin (Windows) or Trash (macOS), from which it can be restored until emptied.

Good practice is a consistent folder structure (by project, year or subject), clear descriptive names, and keeping personal files in the user's own folders (Documents, Pictures, Downloads) so permissions and backups cover them.

Naming restrictions

Every OS reserves some characters. Windows file and folder names cannot contain \ / : * ? " < > |, because those characters already mean something in paths and commands (the colon follows a drive letter, the slashes separate folders, * and ? are wildcards). Windows also reserves device names such as CON, PRN, AUX, NUL, COM1 and LPT1, and very long full paths can cause problems in older software. Spaces, digits, hyphens and periods are allowed. Linux forbids the forward slash (it separates folders); macOS reserves it at the file-system level too, and the Finder rejects the colon. Linux names are case-sensitive, so Report.txt and report.txt are different files there.

A file extension is the set of characters after the last period in a file name, and the OS uses it to decide what type of file it is and which program opens it. Common extensions:

Windows hides known extensions by default, which attackers exploit with double extensions: a file named statement.docx.exe displays as statement.docx, but the OS goes by the last extension, so it is a program that runs when opened. Showing file extensions in File Explorer makes such disguises visible. Renaming an extension does not convert a file's contents; it only changes which program the OS tries to open it with.

Compression makes data take up less space, and archive tools also bundle many files into one file; encryption makes data unreadable to anyone without the right key. They solve different problems: compress to save space or to bundle files for storage and transfer; encrypt to keep data confidential.

Compression is either lossless — the original is restored exactly, as with .zip archives and NTFS compression, required for documents and programs — or lossy, which discards detail people barely notice to shrink files much further, as with JPEG photos, MP3 audio and MP4 video. Because JPEG, MP3 and MP4 files are already compressed, zipping them saves very little space.

Encryption comes in two scopes, and the threat decides which you need:

Permissions decide which users may do what with a file or folder; attributes are flags stored with the file that apply to everyone; properties describe the file. Permissions are an access-control feature, and the rule for setting them is least privilege: give each user the smallest permission that lets them do their job.

So view-only access is Read. Saving edits to existing documents in practice usually needs Modify rather than Write alone, because many applications save by writing a temporary file and then deleting or replacing the original, which requires delete rights. Full control adds changing permissions and taking ownership, which few users need. Linux and macOS use the same idea with three basic permissions — read (r), write (w) and execute (x) — set for the owner, the group and everyone else.

Properties are what the Properties (Windows) or Get Info (macOS) window shows: name, type, location, size and size on disk, dates created, modified and accessed, owner, and — on the Security tab — the permissions. Attributes are set from the same window.

A process is a program that is currently running, with its own memory and an ID number; one application can run several processes. A service (called a daemon on Linux and macOS) is a background program with no window that the OS can start at boot, before anyone signs in, and that keeps running regardless of which user is signed in; a service can be set to start automatically, manually or not at all, and to restart itself if it stops. A startup app is different: it launches when a particular user signs in and closes when that user signs out. A driver is software that lets the OS communicate with a specific hardware device.

To stop a service permanently, change its startup type to Manual or Disabled in the Services console. Stopping it once does not change how it starts next time, and a service whose recovery options are set to restart can be started again by the OS.

Drivers

New hardware usually needs its driver before the OS can use it fully. Windows ships many built-in (inbox) class drivers that are the correct, fully featured driver for standard devices such as USB storage, keyboards, mice and USB audio, so a Microsoft-supplied driver is often exactly right. Some generic drivers are only a fallback: the Microsoft Basic Display Adapter, for example, appears when the graphics card's own driver is not installed, and the card needs that driver for its full capabilities. Device Manager shows which driver each device uses and flags devices with problems. A driver runs in the OS; firmware runs inside the device itself.

System applications and utilities

Disk Cleanup removes files; Disk Management changes partitions. Neither defragments a drive — that is Defragment and Optimize Drives.