Operating Systems - Chapter 13-15

hard disk drive (HDD)

A secondary storage device based on mechanical components, including spinning magnetic media platters and moving read-write heads.

nonvolatile memory (NVM)

Persistent storage based on circuits and electric charges.

platter

An HDD component that has a magnetic media layer for holding charges.

disk arm

An HDD component that holds the read-write head and moves over cylinders of platters.

track

On an HDD platter, the medium that is under the read-write head during a rotation of the platter.

sectors

On an HDD platter, a fixed-size section of a track.

cylinder

On an HDD, the set of tracks under the read-write heads on all platters in the device.

transfer rate

The rate at which data flows.

positioning time

On an HDD, the time it takes the read-write head to position over the desired track.

seek time

On an HDD, the time it takes the read-write head to position over the desired cylinder.

rotational latency

On an HDD, the time it takes the read-write head, once over the desired cylinder, to access the desired track.

head crash

On an HDD, a mechanical problem involving the read-write head touching a platter.

effective transfer rate

The actual, measured transfer rate of data between two devices (such as a computer and a disk drive).

solid-state disk

A disk-drive-like storage device that uses flash-memory-based nonvolatile memory.

USB drive

Nonvolatile memory in the form of a device that plugs into a USB port.

flash translation layer (FTL)

For nonvolatile memory, a table that tracks currently valid blocks.

garbage collection

In general, recovery of space containing no-longer-valid data.

over-provisioning

In non-volatile memory, space set aside for data writes that is not counted in the device free space.

wear leveling

In nonvolatile memory, the effort to select all NAND cells over time as write targets to avoid premature media failure due to wearing out a subset of cells.

RAM drives

Sections of a system's DRAM presented to the rest of the system as if they were secondary storage devices.

magnetic tape

A magnetic media storage device consisting of magnetic tape spooled on reels and passing over a read-write head. Used mostly for backups.

I/O bus

A physical connection of an I/O device to a computer system.

advanced technology attachment (ATA)

An older-generation I/O bus.

eSATA

A type of I/O bus.

serial-attached SCSI (SAS)

A common type of I/O bus.

universal serial bus (USB)

A type of I/O bus.

fibre channel (FC)

A type of storage I/O bus used in data centers to connect computers to storage arrays. A storage-attachment network.

NVM express (NVMe)

A high-speed I/O bus for NVM storage.

controller

A special processor that manages I/O devices.

host bus adapter (HBA)

A device controller installed in a host bus port to allow connection of one or more devices to the host.

host controller

The I/O-managing processors within a computer (e.g., inside a host bus adapter).

device controller

The I/O managing processor within a device.

logical blocks

Logical addresses used to access blocks on storage devices.

constant linear velocity (CLV)

A device-recording method that keeps a constant density of bits per track by varying the rotational speed of the medium.

constant angular velocity (CAV)

A device-recording method in which the medium spins at a constant velocity and the bit density decreases from inner to outer tracks.

low-level formatting

The initialization of a storage medium in preparation for its use as a computer storage device.

physical formatting

The initialization of a storage medium in preparation for its use as a computer storage device.

partition

Logical segregation of storage space into multiple area; e.g., on HDDs, creating several groups of contiguous cylinders from the devices' full set of cylinders.

mounting

Making a file system available for use by logically attaching it to the root file system.

volume

A container of storage; frequently, a device containing a mountable file system (including a file containing an image of the contents of a device).

logical formatting

The creation of a file system in a volume to ready it for use.

cluster

In Windows storage, a power-of-2 number of disk sectors collected for I/O optimization.

raw disk

Direct access to a secondary storage device as an array of blocks with no file system.

bootstrap

The set of steps taken at computer power-on to bring the system to full operation.

boot disk

A disk that has a boot partition and a kernel to load to boot the system. A device that has a boot partition and can store an operating system for booting the computer.

system disk

A storage device that has a boot partition and can store an operating system and other information for booting the computer.

boot partition

A storage device partition containing an executable operating system.

master boot record (MBR)

Windows boot code, stored in the first sector of a boot partition.

boot sector

The first sector of a Windows boot device, containing the bootstrap code.

bad block

An unusable sector on an HDD.

sector sparing

The replacement of an unusable HDD sector with another sector at some other location on the device.

sector slipping

The renaming of sectors to avoid using a bad sector.

swap-space management: The low-level operating-system task of managing space on secondary storage for use in swapping and paging.

raw partition

A partition within a storage device not containing a file system.

anonymous memory

Memory not associated with a file. Pages not associated with a file, if dirty and paged out, must not lose their contents and are stored in swap space as anonymous memory.

page slot

In Linux swap-space management, a part of the data structure tracking swap-space use.

swap map

In Linux swap-space management, a part of the data structure tracking swap-space use.

Host-attached storage

It is storage accessed through local I/O ports. These ports use several technologies, the most common being SATA, as mentioned earlier. A typical system has one or a few SATA ports.

Network-attached storage (NAS)

Provides access to storage across a network. An NAS device can be either a special-purpose storage system or a general computer system that provides its storage to other hosts across the network. Clients access network-attached storage via a remote-procedure-call interface such as NFS for UNIX and Linux systems or CIFS for Windows machines. The remote procedure calls (RPCs) are carried via TCP or UDP over an IP network—usually the same local-area network (LAN) that carries all data traffic to the clients. The network-attached storage unit is usually implemented as a storage array with software that implements the RPC interface.

host-attached storage

Storage accessed through local I/O ports (directly attached to a computer, rather than across a network or SAN).

fibre channel (FC)

A type of storage I/O bus used in data centers to connect computers to storage arrays. A storage-attachment network.

network-attached storage (NAS)

Storage accessed from a computer over a network.

iSCSI

The protocol used to communicate with SCSI devices; used across a network for more distant access.

cloud storage

Storage accessed from a computer over a network to a distant, shared resource data center.

storage-area network (SAN)

A local-area storage network allowing multiple computers to connect to one or more storage devices.

InfiniBand (IB)

A high-speed network communications link.