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--- hardware:recording-technologies [2026/09/23 01:48] – [Ablative (WORM)] wording hbm
+++ hardware:recording-technologies [2026/10/02 17:06] (current) – major rewrite hbm
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 ====== Recording Technologies ======
-Many [[extras:glossary|Disc-Based Enclosed Media (DBEM)]] formats look similar on the exterior, but use different underlying recording technologies. There are three main kinds of recording methods for optical disks; ablative (WORM), magneto-optical, and phase-change.
+Many [[extras:glossary#disc-based_enclosed_media_dbem|Disc-Based Enclosed Media (DBEM)]] formats look alike on the outside, but the way they store data differs. Nearly all can be broadly grouped into one of three recording methods: ablative (WORM), magneto-optical, or phase-change. Knowing which method a disk uses tells you whether it can be rewritten, which drives can handle it, and how it should be stored. Some formats use specialized or hybrid recording techniques, so these categories are best understood as a practical overview rather than an exhaustive classification.
 ===== Ablative (WORM) =====
-This is a strictly Write-Once, Read-Many (WORM) format that relies on physical ablation. When data is written, a high-powered laser beam physically melts, burns, or vaporizes microscopic pits or bubbles into the active recording layer of the disk. Because this causes a permanent physical deformation of the material surface, the data cannot be erased or overwritten, achieving a permanent, tamper-proof archival record(([[https://en.wikipedia.org/wiki/Ablation|Wikipedia — Ablation]])). This recording method can be used for secure data erasure as all traces of the original data can be destroyed instead of overwritten or obscured.
+Ablative media is strictly Write-Once, Read-Many (WORM). To record, a high-powered laser permanently alters — or //ablates//(([[https://en.wikipedia.org/wiki/Ablation|Wikipedia — Ablation]])) — the disk's active recording layer, typically by melting, vaporizing, or otherwise physically modifying a microscopic region. Depending on the particular technology, this can produce pits, bubbles, voids, or other irreversible changes that alter the way the area reflects or transmits light. Because the recording change is permanent, data cannot normally be erased or overwritten, making ablative media suitable for applications where a permanent archival record is desired; removing the recorded data therefore requires physically damaging or destroying the relevant recording layer or disk(([[https://en.wikipedia.org/wiki/Write_once_read_many|Wikipedia — Write once read many]])).
 ===== Magneto-Optical =====
+Magneto-optical (MO) media records data by magnetizing a recording layer, while using a laser to make that layer temporarily susceptible to magnetic changes. The recording layer is a magnetic material that remains stable at room temperature, so ordinary magnetic fields generally cannot alter recorded data. To write, the laser heats a tiny spot toward its Curie temperature, where the material's resistance to magnetization is greatly reduced, and a magnetic field sets the polarity of the spot as it cools. To read the data, a weaker laser beam is reflected from the recording layer. The magnetization changes the polarization of the reflected light through the magneto-optic Kerr effect, and the drive detects that change.
+Conventional MO media is fully rewritable and has a reputation for durability and long data life. Early MO drives generally required separate erase and write operations, while later technologies such as direct overwrite (DO) allowed certain MO media to be rewritten in a single recording operation. Light Intensity Modulated Direct OverWrite (LIMDOW) was one such direct-overwrite technology. WORM versions of some MO formats also exist; these use media and recording structures designed to prevent normal rewriting rather than relying on the physical ablation process used by ablative WORM media.
 ===== Phase-Change =====
+Phase-change media works by using a laser to rapidly alter the physical state of a microscopic recording layer between crystalline (ordered) and amorphous (disordered) structures. The crystalline state reflects light more efficiently, while the amorphous state is less reflective, creating a measurable difference between recorded and unrecorded regions.
+To write data, a high-power laser pulse melts a tiny region of the recording layer, which cools rapidly enough to become amorphous. To erase or overwrite it, a lower-power, longer pulse reheats the region without melting it, allowing it to recrystallize. A low-power read beam then scans the track and detects the difference in reflected light between the two states. Because both recording and erasing are accomplished by controlled laser heating, phase-change media requires no magnetic field for writing and can support single-pass rewriting in formats designed for direct overwrite. The technology is used in several rewritable optical formats.
+===== Quick Comparison =====
+^ Method          ^ Rewritable? ^ Written by                                    ^ Read by ^
+| Ablative (WORM) | No          | Laser creates an irreversible physical change | Optical signal from a reflectivity or transmission change |
+| Magneto-optical | Yes((Some magneto-optical formats use WORM media and are therefore not rewritable.))         | Laser heat + magnetic field                   | Polarization rotation (Kerr effect)                       |
+| Phase-change    | Yes         | Laser heat only                               | Optical signal from a reflectivity change                 |