OS Types, Filesystems & Compatibility

The operating system is the software that makes hardware useful to humans. Before learning how to install, configure, or troubleshoot one, you need to know the landscape: what operating systems exist, which filesystems they use, how long vendors support them, and what happens when you mix components that were not designed to work together.

This lesson gives you that map. The details of configuring each OS — Windows editions, macOS tools, Linux commands — come in Lessons 3 through 9. Here, you learn what exists and why it matters.

Workstation Operating Systems

A workstation OS is an operating system designed for general-purpose computing on a desktop or laptop. The four you need to know for A+:

Windows is the dominant OS in enterprise environments and the most common workstation OS in the world. It runs on standard x86/x64 hardware from any manufacturer. The versions in scope for 220-1202 are Windows 10 and Windows 11 — both are tested, and exam questions will specify which version applies when features differ. Windows dominates corporate IT because of its enterprise tooling: Active Directory integration, Group Policy, widespread application support, and a large pool of trained administrators.

Linux is open-source and available in dozens of distributions: Ubuntu and Debian (consumer and developer friendly), Red Hat Enterprise Linux (RHEL) and CentOS (enterprise servers), Fedora (developer-focused community release). Linux is free, highly customizable, and dominant in server environments, cloud infrastructure, and embedded systems. No one version of Linux is "the standard" — distributions package the same Linux kernel with different default software, package managers, and support models. Lesson 9 covers Linux tools in detail.

macOS is Apple's proprietary operating system, running exclusively on Apple hardware — both Intel-based Macs and Apple Silicon (ARM) Macs. macOS is Unix-based, descending from BSD Unix and sharing command-line heritage with Linux. It dominates creative, design, and education environments. Because it runs only on Apple hardware, macOS removes driver compatibility complexity that plagues Windows administrators. Lesson 8 covers macOS features.

Chrome OS is Google's operating system designed for Chromebooks. Chrome OS is built around the Chrome browser — most applications run as web apps, with limited local storage and offline capability by design. Chrome OS supports Android apps through the Google Play Store, expanding its application library beyond web apps — flag for verification. Chrome OS is common in K-12 education for its low cost and minimal administrative overhead.

Mobile Operating Systems

iOS is Apple's operating system for iPhones. It is a closed ecosystem: Apple controls the hardware, the OS, and the application distribution channel via the App Store. You covered iOS characteristics in the Core 1 Mobile module — this lesson does not re-teach them.

iPadOS is Apple's OS for iPads. Apple separated iPadOS from iOS in 2019 — prior to that, iPads ran iOS — flag this split year for verification. iPadOS is based on the same codebase as iOS but adds iPad-specific features: improved multitasking, external display support, and desktop-class browser behavior. For A+ purposes, treat iPadOS as iOS with tablet extensions.

Android is Google's mobile OS, based on the Linux kernel. Unlike iOS, Android is open-source at its base — hardware manufacturers customize it for their devices. Android allows installation of apps from the Google Play Store and, depending on device settings, from outside the Play Store (sideloading). You covered Android in the Core 1 Mobile module.

Filesystem Types

A filesystem is the structure an OS uses to organize, store, and retrieve data on a storage device. The filesystem determines the maximum file size, the maximum volume size, whether the OS supports permissions and encryption at the filesystem level, and which other operating systems can read the drive natively. The A+ exam tests seven filesystems — know all seven.

NTFS (New Technology File System)

NTFS is the default filesystem for Windows internal drives — it is what Windows installs onto and what most Windows drives use in production.

Key capabilities:

• Journaling: NTFS logs changes before committing them, allowing recovery from incomplete writes caused by crashes or power loss
• Permissions (ACLs): Access Control Lists let administrators grant fine-grained read, write, and execute access per user or group at the file and folder level
• Encryption (EFS): the Encrypting File System encrypts individual files and folders at the filesystem level, tied to the Windows user account
• Compression: NTFS can compress files and folders on disk to save space
• Large file and volume support: NTFS supports individual files up to 16TB (flag for verification) and volumes up to a practical limit of ~256TB (flag for verification)

NTFS has limited write support on macOS — macOS reads NTFS volumes natively but cannot write to them without third-party software by default (flag for verification). Linux can access NTFS using the ntfs-3g driver.

ReFS (Resilient File System)

ReFS is Microsoft's high-integrity filesystem, designed for large-scale storage on Windows Server and Windows 10/11 Pro for Workstations. It is not a replacement for NTFS on everyday Windows — it targets enterprise storage environments where data integrity at scale matters.

Key characteristics:

• Checksummed data integrity: ReFS uses checksums on metadata and optionally on file data to detect silent corruption; when combined with Storage Spaces, it can self-heal corrupted data
• Large volume support: designed for volumes measured in petabytes
• No compression, no EFS encryption: ReFS deliberately excludes these NTFS features

Critical exam fact: ReFS is not bootable as a Windows system drive — you cannot install Windows on a ReFS volume (flag for verification). It is used for data volumes, never the OS partition.

FAT32 (File Allocation Table 32)

FAT32 is a legacy filesystem dating to 1996. It remains relevant for one reason: it is universally readable across operating systems — Windows, macOS, and Linux all support FAT32 natively without additional software or drivers.

The price of that compatibility is strict size limits:

• Maximum file size: 4GB minus 1 byte — flag for verification. Any single file 4GB or larger cannot be stored on a FAT32 volume. This is the most directly exam-tested FAT32 fact.
• Maximum volume size when formatted by Windows: 32GB — flag for verification. Windows' built-in format tool will not create a FAT32 volume larger than 32GB.

FAT32 has no journaling, no permissions, and no encryption. These limitations make it unsuitable for Windows or macOS system drives, but ideal for USB drives that must be readable everywhere.

exFAT (Extensible File Allocation Table)

exFAT is Microsoft's successor to FAT32, designed to fix FAT32's file size limitation while preserving cross-platform compatibility. exFAT is natively supported by Windows, macOS, and modern Linux (kernel 5.4+ — flag for verification).

Key properties:

• No practical file size limit: exFAT supports individual files up to 16EB — effectively unlimited for any real-world use
• Cross-platform: natively readable and writable on Windows, macOS, and Linux without third-party tools
• No journaling: like FAT32, exFAT does not journal, making it more vulnerable to corruption from sudden power loss than NTFS or ext4
• Common use: USB drives and SD cards where individual files exceed 4GB (video files, disk images, large databases)

ext4 (Fourth Extended Filesystem)

ext4 is the default filesystem for most Linux distributions — Ubuntu, Debian, Linux Mint, and many others use ext4 by default. It is a journaling filesystem with deep Linux OS integration.

Key properties:

• Journaling: logs changes before writing, similar to NTFS
• Large file support: supports files up to 16TB and volumes up to 1EB
• Linux permissions: integrates with the Linux user/group ownership model (uid/gid), which is how Linux filesystem security works

ext4 is not natively readable by Windows — accessing an ext4 volume on Windows requires third-party tools. macOS also does not read ext4 natively.

XFS

XFS is a high-performance journaling filesystem and the default for Red Hat Enterprise Linux (RHEL) and CentOS — the enterprise Red Hat family of Linux distributions. It was originally developed by Silicon Graphics for high-throughput workloads and is optimized for:

• Large files and high throughput: fast sequential I/O; strong performance with very large files
• High-concurrency: handles many simultaneous I/O operations well
• Large volumes: designed to scale to very large storage

For A+, the key fact is the association: XFS = RHEL and CentOS server environments. You do not need to know XFS internals beyond this mapping.

APFS (Apple File System)

APFS is Apple's modern filesystem, introduced in macOS High Sierra (2017) — flag this year for verification. APFS replaced HFS+ (also called Mac OS Extended) across the entire Apple product line and is now the default filesystem for macOS, iOS, iPadOS, tvOS, and watchOS.

Key capabilities:

• Encryption: APFS supports full-volume encryption natively, integrated with FileVault on macOS
• Snapshots: APFS can take point-in-time snapshots of a volume — used by Time Machine for backups
• Space sharing: multiple APFS volumes on the same container share available space dynamically rather than having fixed partition sizes
• Copy-on-write: changes are written to new locations before the old data is released, protecting integrity if a write is interrupted

Windows does not natively read or write APFS volumes. Third-party tools are required to access APFS drives on Windows.

Filesystem Quick Reference

| Filesystem | Primary OS | Journaling | Max File Size | Notable Limits / Notes | |---|---|---|---|---| | NTFS | Windows | Yes | 16TB† | Default Windows; permissions, EFS; read-only on macOS by default | | ReFS | Windows Server | Yes | Very large | NOT bootable; no EFS, no compression | | FAT32 | Cross-platform | No | 4GB | 32GB volume limit (Windows format); no permissions | | exFAT | Cross-platform | No | No limit | FAT32 successor; used on USB/SD | | ext4 | Linux | Yes | 16TB | Linux default; not natively readable on Windows or macOS | | XFS | Linux (RHEL/CentOS) | Yes | Large | RHEL/CentOS default; high-throughput | | APFS | macOS/iOS | No (CoW†) | Very large | Replaces HFS+; snapshots, encryption; Windows needs third-party tool |

†Figures marked are flagged for verification in the fact-check.

Vendor Life-Cycle Limitations

Every operating system has a product life cycle — a defined period during which the vendor releases security patches, bug fixes, and feature updates. When that period ends, the OS reaches End of Life (EOL).

What EOL means:

• The vendor stops releasing security patches for that OS version
• Vulnerabilities discovered after EOL are never fixed — they exist in the OS permanently
• A machine running an EOL OS accumulates unpatched vulnerabilities with no remedy from the vendor

Why it matters for a technician: EOL systems cannot be secured by patching — there are no patches to apply. The correct responses are:

1. Replace the OS with a supported version
2. Isolate the system from the network to limit exposure
3. Accept and document the risk (only for edge cases — legacy industrial or medical hardware that cannot be updated)

Windows life-cycle reference:

• Windows 7 reached EOL on January 14, 2020
• Windows 10 mainstream support ended October 14, 2025 — flag for verification; verify against the Microsoft Product Life Cycle page before advising customers, as support dates can change

Compatibility Concerns

32-bit vs 64-bit

Modern CPUs are 64-bit, but the software ecosystem still includes both 32-bit and 64-bit applications. The rules:

• A 64-bit OS can run both 64-bit and 32-bit applications. On Windows, 32-bit application support is provided by WOW64 (Windows 32-bit on Windows 64-bit) — flag name and function for verification. WOW64 is a compatibility layer built into 64-bit Windows that translates 32-bit API calls so 32-bit applications run without modification.
• A 32-bit OS can only run 32-bit applications. 64-bit applications require the 64-bit instruction set and will not execute on a 32-bit OS.
• Drivers must match the OS architecture. A 32-bit driver cannot load into a 64-bit OS kernel. When upgrading from a 32-bit to 64-bit OS, all drivers must be replaced with 64-bit versions.

Driver Compatibility

Drivers are specific to the operating system version and the CPU architecture. A driver written for Windows 10 may not be signed for Windows 11; a driver for a 32-bit OS will not load on a 64-bit OS. Before committing to an OS upgrade, verify that all required drivers have a compatible version for the target OS. Missing drivers after an upgrade are a common source of non-functional peripherals.

Cross-OS File Sharing

The filesystem on a drive determines which operating systems can read or write it natively:

| Filesystem | Windows | macOS | Linux | |---|---|---|---| | NTFS | Full read/write | Read-only by default* | Full (via ntfs-3g) | | FAT32 | Full | Full | Full | | exFAT | Full | Full | Full (kernel 5.4+) | | ext4 | Needs tool | Needs tool | Full | | APFS | Needs tool | Full | Needs tool |

*macOS NTFS write limitation — flag for verification.

The safest cross-platform format for a USB drive is exFAT when files may exceed 4GB, or FAT32 when maximum compatibility with older systems is needed and all files stay under 4GB. NTFS limits you to read-only on macOS by default; ext4 and APFS require third-party tools on non-native platforms.

The check questions below test your ability to apply these filesystem limits, OS-to-filesystem associations, and compatibility rules to real technician scenarios.