What is ISO?
In IT, ISO has two meanings, and the context makes clear which one is meant:
- The International Organization for Standardization, an independent, non-governmental body based in Geneva whose members are national standards bodies. ANSI is the US member. ISO publishes standards across every industry. The short name is not an English acronym; ISO says it comes from the Greek word isos, meaning equal, so the name is the same in every language.
- An ISO image file (.iso), a single file that holds a complete copy of an optical disc's contents and file system. The name comes from ISO 9660, the standard file system for CD-ROMs. Many current images, including Windows installation media, use the newer Universal Disk Format (UDF) inside, but the .iso extension stayed.
ISO standards IT staff run into
| Standard | What it covers |
|---|---|
| ISO/IEC 27001 | Information security management systems; organizations are audited and certified against it |
| ISO/IEC 27002 | Guidance on the security controls used with 27001 |
| ISO 9001 | Quality management systems |
| ISO/IEC 17024 | Requirements for bodies that certify people; the CompTIA A+ exams are accredited by ANSI to this standard |
| ISO/IEC 7498-1 | The OSI reference model, the seven-layer networking model |
| ISO 9660 | The CD-ROM file system that gave .iso files their name |
Many ISO standards in IT are published jointly with the IEC (International Electrotechnical Commission), which is why they carry the ISO/IEC prefix.
Working with ISO image files
- Mount it. In Windows, double-click an .iso file or right-click it and choose Mount. It appears as a virtual DVD drive with its own drive letter; eject it to unmount. PowerShell does the same with
Mount-DiskImage -ImagePath. On Linux,mount -o loop file.iso /mnt/isomounts it, and macOS mounts an ISO when you double-click it. - Burn it. Windows can write an ISO to a blank disc with the right-click Burn disc image option.
- Make bootable USB media. Copying the .iso file onto a USB drive does not make the drive bootable. The image has to be written to the drive with a tool built for that job, such as Microsoft's Media Creation Tool for Windows or a USB image-writing utility.
- Install a virtual machine. Hypervisors such as Hyper-V, VirtualBox, and VMware attach an ISO to the VM's virtual optical drive so the guest operating system can be installed from it.
- Verify it. Compare the file's hash with the one the publisher lists, using
Get-FileHashin PowerShell (SHA-256 by default) orsha256sumon Linux. A mismatch means a corrupted or tampered download.
Many current operating system images are larger than 4 GB, so they cannot be stored as a single file on a FAT32 drive. Use exFAT or NTFS when you only need to carry the file.
ISO on the CompTIA A+ exam
ISO appears on the Core 1 acronym list as International Organization for Standardization, and the objectives document notes that the A+ exams are accredited to ISO 17024. ISO image files come up in Core 2 operating system installation, where they are the usual source for installation media, and in virtualization scenarios where a guest OS is installed from an attached image. Know both senses. Words such as mount, burn, boot from, or attach to a VM point to an image file; words such as compliance, certification, or 27001 point to the standards organization.