A sector is a fixed-size “chunk” of information as stored on magnetic or other media such as hard disks, optical discs, and flash-based memory.
A sector most commonly contains 4096 bits, or 512 bytes. (Newer hard drives may use 32,768 bit – aka 4096 byte – sectors, but for compatibility with older interfaces and operating systems, may also expose a simulation of 512 byte sectors.)
Sectors are accessed as single units at the hardware level. This means that when reading, the entire sector is read, regardless of how much of its contents are required. Similarly, when writing data, it’s the entire sector that’s written, regardless of how much information in it is to be changed.
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