An optical drive reads and writes data on discs like CDs, DVDs, and Blu-ray discs by using a laser beam. It’s the slot or tray on a computer (or a standalone external device) that accepts shiny, flat discs and translates the microscopic patterns on their surface into usable files, music, video, or software.
How a Laser Reads a Disc
The surface of an optical disc is covered in a spiral track of tiny bumps called “pits” and flat areas called “lands.” When the drive spins the disc, a laser beam hits this surface and bounces back toward a light sensor. Pits and lands reflect light differently because of their uneven surfaces, and the sensor picks up those changes in reflected light. The drive converts each change into an electrical signal, which a processor then interprets as binary data: the ones and zeros that make up every file on the disc.
Think of it like Morse code written in bumps. The laser scans the spiral track from the inside of the disc outward, and the pattern of reflections tells the drive exactly what data is stored there. Because the laser never physically touches the disc surface, the reading process causes no mechanical wear on the media itself.
CDs, DVDs, and Blu-ray Use Different Lasers
The three major disc formats each use a different wavelength of laser light, which determines how small the pits and lands can be and, ultimately, how much data fits on a disc.
- CD drives use an infrared laser at 780 nanometers. A standard CD holds about 650 to 700 MB of data, which translates to roughly 80 minutes of audio.
- DVD drives use a red laser at 650 nanometers. The shorter wavelength reads a smaller spot on the disc, which raised single-layer capacity fivefold to 4.7 GB.
- Blu-ray drives use a blue-violet laser at 405 nanometers. That tiny 150-nanometer spot size allows a single-layer Blu-ray disc to store over 25 GB, enough for high-definition video.
A shorter wavelength means a more tightly focused beam, which means pits can be packed closer together. That’s the core reason each new format held dramatically more data than the last. Most modern optical drives are backward-compatible, so a Blu-ray drive can also read DVDs and CDs.
How Burning a Disc Works
Reading is only half of what many optical drives do. Drives labeled as “writers” or “burners” can also record data onto blank discs. The process works differently from reading. Instead of bouncing a low-power laser off existing pits, the drive cranks up the laser’s intensity to physically alter the disc’s recording layer.
On a recordable CD or DVD (CD-R, DVD-R), the disc contains a thin layer of transparent organic dye over a reflective surface. The high-powered laser scorches dark spots into this dye, creating artificial pits that behave like the factory-pressed ones. Once burned, these marks are permanent, which is why recordable discs can’t be erased. Rewritable discs (CD-RW, DVD-RW) use a different material that can switch between crystalline and amorphous states, allowing data to be written, erased, and rewritten hundreds of times.
Data Transfer Speeds
Optical drive speeds are measured in multiples of a base “1x” rate, which is different for each format. For CDs, 1x equals 0.15 MB per second. For DVDs, 1x is 1.38 MB per second. For Blu-ray, 1x is 4.5 MB per second. A drive marketed as “16x DVD” reads DVDs at roughly 22 MB per second.
These speeds are modest compared to modern solid-state drives or even USB flash drives. A typical external optical drive connected over USB 3.0 won’t bottleneck on the USB connection. The disc’s spin speed is the limiting factor, not the cable.
Internal vs. External Drives
Throughout the 2010s, laptop manufacturers stopped including built-in optical drives. Removing them made laptops thinner and lighter, freed up internal space for larger batteries or circuit boards, and cut production costs. The rise of cheap, high-capacity USB flash drives and streaming video made the trade-off easy for most buyers.
If you need an optical drive today, external models connect via USB 3.0 or USB-C and draw power directly from the port, so no separate power adapter is needed. They’re backward-compatible with USB 2.0 as well. You plug one in, insert a disc, and your computer treats it like any other drive. Desktop computers occasionally still have a 5.25-inch bay for an internal drive, but external units work identically and are more practical for most setups.
Common Uses for an Optical Drive
Even as streaming and cloud storage dominate, optical drives still fill several roles. Installing older software that shipped on disc, ripping a CD collection to digital audio files, playing or backing up DVDs and Blu-rays, and burning data archives are the most common reasons people still use one. Some industries, like healthcare and legal services, rely on optical media for distributing records because a burned disc is a simple, self-contained package that doesn’t require an internet connection to access.
For long-term archiving, specialized discs called M-Discs engrave data into a rock-like inorganic layer instead of organic dye. Standard recordable discs can last a decade or more under normal conditions, but they’re sensitive to scratches, heat, and humidity. M-Discs are significantly more durable, making them a low-cost option for archival storage that you don’t plan to touch for many years. Real-world tests show standard Blu-ray discs burned over a decade ago still reading without errors, but M-Discs offer an extra margin of safety for anything truly irreplaceable.
Who Still Needs One
If your media library is entirely digital, you stream all your video, and you install software through downloads, you can comfortably skip an optical drive. But if you have a shelf of DVDs, a box of old software discs, or a need to create physical backups that aren’t dependent on cloud services or hard drive reliability, an external optical drive is an inexpensive tool (typically $20 to $40) that fills gaps no other device quite covers.