USB mass storage device class
Protocol making USB devices accessible as external hard drives.
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The USB mass storage device class (also known as USB MSC or UMS) is a set of computing communications protocols, specifically a USB Device Class, defined by the USB Implementers Forum. It makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device. To a host, the USB device acts as an external hard drive; the protocol sets interfaces with a number of storage devices.
Quick Facts
- Defined by
- USB Implementers Forum
- Also known as
- USB MSC or UMS
- First windows support
- Windows 2000
- First linux kernel support
- Version 2.3.47 (2001, backported to kernel 2.2.18)
- First solaris support
- Version 2.8 (1998)
- First freebsd support
- Version 4.0 (2000)
- First netbsd support
- Version 1.5 (2000)
Facts from the source article.
Background
The USB mass storage device class provides an interface to a number of industry-standard command sets, allowing a device to disclose its subclass. In practice, there is little support for specifying a command set via its subclass; most drivers only support the SCSI transparent command set, designating their subset of the SCSI command set with their SCSI Peripheral Device Type (PDT). Subclass codes specify command sets including Reduced Block Commands (RBC), SFF-8020i/MMC-2 (for ATAPI-style CD and DVD drives), QIC-157 (tape drives), Uniform Floppy Interface (UFI), SFF-8070i (for ARMD-style devices), and the SCSI transparent command set.
The specification does not require a particular file system on conforming devices. Based on the specified command set and any subset, it provides a means to read and write sectors of data.
Operating systems may treat a USB mass-storage device like a hard drive; users may partition it in any format (such as MBR and GPT), and format it with any file system. Because of its relative simplicity, the most common file system on embedded devices such as USB flash drives, cameras, or digital audio players is Microsoft's FAT or FAT32 file system (with optional support for long filenames). However, USB mass storage devices may be formatted with any other file system, such as NTFS on Windows NT, HFS Plus on macOS, ext2 on Linux, or Unix File System on Solaris or BSD.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: USB mass storage device class (CC BY-SA 4.0).
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