Live CD facts for kids
A live CD is a special computer setup that includes a full operating system. It runs directly from a CD-ROM or a similar storage device. This means it loads into your computer's memory instead of installing onto your hard drive. You can use a live CD to run an operating system without installing it. It won't change your computer's settings.
Live CDs are great because they can work even if your computer doesn't have a hard drive. They also work if your hard drive is broken. This makes them very useful for data recovery, which is getting back lost files.
Today, CD and DVD drives are less common. So, live CDs are not as popular as they once were. Now, people often use live USBs instead. These are similar systems saved onto a USB flash drive. USB drives are handy because you can also save files on them. You can also use an external hard drive connected by USB for the same purpose. Some live CDs let you save your work by writing files to a hard drive or USB drive. This is called persistence.
Many Linux distributions offer special files called ISO images. You can burn these files onto a CD or DVD. Most open-source operating systems are free to use. However, some paid software, like Windows To Go, needs a license. Live CDs are often used for many tasks. These include getting back data, checking computers for clues (forensics), making copies of disks, fixing systems, and removing harmful software (malware). For example, the Tails operating system helps users stay private and anonymous. It lets them work with important documents without leaving traces on the computer.
Contents
How Live CDs Started
All computers, except the very first ones, have a small program built-in. This program helps the computer start up. It loads other programs from a storage device. In the past, computers used things like punched tape or cards to start. Later, floppy disks and hard disks became common for starting computers.
The compact disc (CD) was first used for music. But soon, people started using it to store large amounts of computer data. This data could include programs and operating systems. People realized it was useful to start a computer directly from a CD. This often included a small working system. This small system could then install a full operating system onto a hard drive. Most CDs used for this were read-only.
Early CD drives on personal computers were quite slow. Computers were also not designed to start from a CD. When operating systems came on CDs, they usually only booted to install onto a hard drive. Some of the first operating systems that could run directly from a CD were the Towns OS and VMS. Both came out in 1989.
Linux and Live CDs
Early users of Linux could use cheap optical disks. But these Linux CDs were mostly for installing software onto hard drives. At that time, many people didn't want to install Linux. They found it hard or risky to add it next to their existing operating system.
The name "live CD" became popular later. This happened when computer memory (RAM) became larger. Also, CD drives became much faster. It finally became easy to run Linux and its graphical interface directly from a CD. This meant you didn't have to change anything on your hard drive. This was a big deal for Linux. Updates came out quickly, and users were burning their own CDs.
The first Linux-based live CD was Yggdrasil Linux. It came out in 1992-1993. But it was slow because CD-ROM drives were not very fast yet. DemoLinux, released in 1998, was the first Linux version made especially as a live CD. The Linuxcare bootable business card (1999) was the first live CD for fixing computer systems.
As of As of 2023[update], Finnix (first released in 2000) is the oldest live CD still being made. Knoppix, a popular Linux version, came out in 2003. It became well-known as a way to fix computers and as a main operating system. Since 2003, live CDs have become much more popular. This is partly thanks to tools like Linux Live scripts. These tools made it easy to create custom live systems. Today, most popular Linux versions include a live CD option. Sometimes, this is even the main way to install them.
What Live CDs Are Used For
Live CDs are made for many different reasons. Some are designed to let you try out an operating system. This is usually Linux or another free or open source system. You can test software or run it for a single task. This won't affect your computer's setup.
If your computer isn't working right, a live CD can help you get your data. For example, you can recover files from a computer with a virus. The virus won't be active and cause more harm. You can also remove the virus more easily.
Some live CDs can load completely into your computer's memory. This frees up the CD drive for other uses. Loading from a CD is slower than from a hard drive. But for smaller live CDs, loading into RAM can make things much faster. This is because RAM is quicker than a hard drive.
Experienced computer users might use a live CD to check hardware. They can see if an operating system works well with their computer parts. This helps them know what will work before buying new equipment. A live CD can also help fix hardware problems, especially if a hard drive fails. It's like a recovery disc for emergencies.
Some live CDs let you save files you create. You can save them to a Windows part of your hard drive, a USB drive, or a network drive. Live backup CDs can also make copies of your drives. They can back up files without problems from open files.
Here are some other uses for live CDs:
- Installing a Linux distribution onto a hard drive.
- Computer forensics: investigating computers for evidence.
- Scanning for viruses and removing malware.
- Repairing systems and recovering data.
- Testing new versions of software.
- Listing and testing computer hardware.
- Using Internet kiosks and public computers. These can be reset to their original state by restarting.
- Providing a secure, temporary environment for a guest user.
- Testing network security.
- Being the main or backup operating system for any computer.
- Quickly connecting computers together for tasks (clustering).
- Playing video games or running apps that need a different operating system.
- Creating a secure server where important files cannot be changed.
- Providing a safe platform for sensitive tasks like internet banking.
- Bypassing parental controls or other computer limits.
Many live CDs are made for specific types of uses. For example, there are live CDs for IT administration, firewalls, or security. Some live DVDs can even cover more than one topic.
Software Appliances
A "software appliance" is a program designed to do a specific job. Packaging it as a live CD can be helpful. This is because one single image can run on both real computers and virtual machines. This helps developers avoid making many different versions for different virtual machine types. They can focus on one common format.
When you start a computer from a live CD, the software appliance usually runs in a "demo mode." This means it doesn't save changes. Or, it can install itself onto a storage device if you choose.
Using Live CD Files Without Burning
You don't always need to burn a live CD ISO image to a disc. You can access the files on it in Microsoft Windows using a disk image emulator. Or, in Unix systems, you can "mount" it like a regular drive. Newer versions of Windows (like Windows 8 and later) let you mount an ISO file directly.
Once the live CD's files are mounted, you can run software from it. You don't even need to boot the whole system. You can also mount a live CD ISO image using Virtual Machine software like VirtualBox or VMware Workstation. Or, you can turn it into a Live USB using tools like SYSLINUX. There are special tools that can do this automatically.
Features of Live CDs
When a live CD starts, you can often use special "boot codes." These codes change how the system starts. They are different for each system. You can usually find them on the first boot screen by pressing a function key.
Some live CDs include a tool to install the system. You can launch this tool from a desktop icon. It lets you install the system onto a hard drive or USB flash drive. Most live CDs can also access information on your computer's internal or external hard drives, diskettes, and USB drives.
Live CDs are usually on read-only discs. This means you can't save new software or changes directly to the CD. To add software, you would need to copy it to a rewriteable drive. However, there are exceptions. If you record Puppy Linux to a special multi-session disc, your changes can be saved. These changes will then be there the next time you boot the CD.
The term "Live CD" now refers to any CD with an operating system and software. This software can run without being installed on the computer. Operating systems that can be used live include AmigaOS 4, FreeBSD, FreeDOS, classic Mac OS, macOS, and Microsoft Windows repair discs. There are also maintenance versions of Windows that can boot from a CD. Examples are BartPE and Windows PE.
The AmigaOS in 1990 might have been the first personal computer operating system on a CD to support "live" use. It could boot from a CD on an Amiga CDTV. Earlier live operating systems existed on floppy disks, like DOS.
Unlike older operating systems on CDs, Linux and OS/2 "live CDs" were made to run without installing. The idea of a live CD was to promote Linux. It showed off the abilities of this free, open source operating system on regular computers that already had Microsoft Windows.
On a PC, a bootable CD usually follows the El Torito standard. This standard was introduced in 1994. Many Linux live CDs use a compressed file system. This often doubles the storage space. However, it can make programs start a bit slower.
The environment you get from a live CD can be very rich. For example, a typical Knoppix system includes about 1,200 different software packages. Live CDs are known for being good at setting themselves up automatically. They also support "plug-and-play" features. This is important because users shouldn't have to set up the system every time they boot it. It also makes them easy for new users to try out.
How Live CDs Are Made
A read-only file system, like on a CD-ROM, cannot save new data. Because of this, a read-only file system is often combined with a temporary writable file system. This temporary system is usually a RAM disk. A RAM disk uses your computer's memory (RAM) to store files. Often, common Linux folders like "`/home`" (for user files) and "`/var`" (for changing data) are kept in RAM. This is because the system updates them often. Puppy Linux and some other live CDs let you save your settings and added files. These changes will then be used in future sessions.
In modern live CDs, the read-only file system is combined with a RAM drive. This is done using special techniques like UnionFS or AuFS. Boot loaders like syslinux can even start ISO files from USB memory devices.
Live CDs need to be able to find and use many different computer parts. This includes network cards and graphic cards. They do this in real-time. They often use features like udev and hotplug. These are common parts of Linux systems.
See also
In Spanish: Live CD para niños
- Boot disk
- Comparison of Linux distributions#Live media
- GIS Live DVD
- List of live CDs
- List of remastering software
- Live USB
- Self-booting diskette
- Software appliance
- Windows To Go
