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Terms and Definitions

The following terms will be used throughout this manual:

Sector

The smallest storage unit which can be read from or written to a mass storage device. For most diskettes and hard disks, one sector has 512 bytes. CD-ROM and DVDs use 2048 bytes per sector. Some newer USB and SATA disks use a sector size of 4096 bytes.

Cluster

A contiguous set of sectors used to allocate file space. On FAT, RTFiles-32 supports cluster sizes of 1, 2, 4, 8, 16, 32, 64, and 128 sectors, as well as extended cluster sizes of up to 32768 sectors per cluster. Extended cluster sizes are not DOS/Windows compatible. On exFAT, up to 65536 sectors per cluster are possible. On ISO 9660 file systems, a cluster is identical with a sector.

Physical Device

A physical mass storage device used to store files. Examples are hard disks, floppy disks, USB sticks, etc.

Device

Alias for Physical Device.

Logical Drive

A portion (or possibly all) of a device holding a file system. Hard disks support several logical drives on a single device through partitions.

Drive

Alias for Logical Drive.

Volume

The media containing one or more logical drives such as a diskette or hard disk.

Partition

A physical portion of a hard disk. With MBR partition tables, hard disks can be divided into up to four primary partitions. A special type of partition (the extended partition) can be subdivided into any number of logical drives. Non-extended partitions can hold exactly one logical drive each. GPT partition tables support up to 128 partitions per disk.

Partition Table

MBR partition tables can hold four entries located in the first physical sector of a hard disk. It describes the primary and extended partitions of the disk. GPT partition tables span several sectors.

FAT

File Allocation Table. A data structure used by FAT file systems to record which clusters are used by each file.

CHS

Cylinder Head Sector. This abbreviation describes the traditional method of addressing sectors on diskettes and legacy hard disks.

LBA

Logical Block Addressing. LBA is a newer method to address sectors on hard disks using a single 64-bit sector index. The translation to a physical CHS value is performed by the disk controller or device driver. CD-ROMs and DVDs always use LBA addressing.

Sector Aligned Access

Reading and writing file data on sector boundaries. The file pointer is always a multiple of the sector size and data is read or written in multiples of the sector size. It does not mean that the data buffer supplied by the application must be aligned in any way.

Device List

A global data structure used by RTFiles-32 to locate all available devices.

File Instance

The RTFiles-32 internal data associated with an open file. When the same disk file is opened several times, several instances of a single file exist simultaneously.

CD-ROM

Campact Disk, Read Only Memory. This manual uses the term CD-ROM or just CD to denote both CD-ROMs and DVDs (Digital Versatile Disc) holding and ISO 9660 file system.

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