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Time Machine is the
backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up", ...
mechanism of
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
, the desktop
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developed by
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
. The software is designed to work with both local storage devices and network-attached disks, and is most commonly used with external disk drives connected using either USB or Thunderbolt. It was first introduced in Mac OS X 10.5 Leopard, which appeared in October 2007 and incrementally refined in subsequent releases of macOS. Time Machine was revamped in
macOS 11 Big Sur macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple Inc.'s operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the public ...
to support APFS, thereby enabling "faster, more compact, and more reliable backups" than were possible previously.


Overview

Time Machine creates incremental backups of files that can be restored at a later date. It allows the user to restore the whole system or specific files. It also works within a number of applications such as
Mail The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal sys ...
and
iWork iWork is an office suite of applications created by Apple Inc. for its macOS and iOS operating systems, and also available cross-platform through the iCloud website. It includes the presentation application Keynote, the word processing and ...
, making it possible to restore individual objects (e.g. emails, contacts, text documents, presentations) without leaving the application. According to an Apple support statement:
“Time Machine is a backup utility, not an archival utility, it is not intended as offline storage. Time Machine captures the most recent state of your data on your disk. As snapshots age, they are prioritized progressively lower compared to your more recent ones.”
For backups to a network drive, Time Machine allows the user to back up Mac computers over the network, and supports backing up to certain network attached storage devices or servers, depending on the version of Time Machine. Earlier versions worked with a wide variety of NAS servers, but later versions require the server to support a recent version of Apple's Apple Filing Protocol (AFP) or a recent version of the Server Message Block (SMB) protocol, and Time Machine no longer works with servers using earlier versions of SMB. Some of the legacy support can be re-enabled by using hand-tuned configuration options, accessed through the
Terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output devi ...
. Apple's
Time Capsule A time capsule is a historic cache of goods or information, usually intended as a deliberate method of communication with future people, and to help future archaeologists, anthropologists, or historians. The preservation of holy relics dates ...
, which was introduced in 2008 and discontinued in 2018, acted as a network storage device specifically for Time Machine backups, allowing both wired and wireless backups to the Time Capsule's internal hard drive. Time Machine may also be used with other external or internal volumes. Time Machine saves hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for everything older than a month until the volume runs out of space. At that point, Time Machine deletes the oldest weekly backup.


Revamp in macOS Big Sur

Time Machine was overhauled in
macOS 11 Big Sur macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple Inc.'s operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the public ...
to utilize APFS, Apple's modern
file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
first introduced in 2016. Specifically, the new version of Time Machine makes use of APFS's snapshot technology. According to Apple, this enables "faster, more compact, and more reliable backups" than were possible previously with
HFS+ HFS Plus or HFS+ (also known as Mac OS Extended or HFS Extended) is a journaling file system developed by Apple Inc. It replaced the Hierarchical File System (HFS) as the primary file system of Apple computers with the 1998 release of Mac OS 8 ...
-formatted drives. An independent evaluation of this claim found that macOS 11's Time Machine implementation in conjunction with APFS was 2.75-fold faster upon initial local backup and 4-fold faster upon subsequent backups relative to macOS 10.15's Time Machine implementation using HFS+. A more modest yet nevertheless significant advantage was noted as well for backups to network-attached disks. New local (i.e. USB- or Thunderbolt-connected) and network-connected Time Machine backup destinations are formatted as APFS by default, though Time Machine can continue backing up to existing HFS+ backup volumes." There is no option to convert existing, HFS+-based backups to APFS; instead, users who want to benefit from the advantages of the new, APFS-based implementation of Time Machine need to start with a fresh volume. At least in some circumstances, encryption appears to be required (instead of merely optional) in the new version of Time Machine.


User interface

Time Machine's
user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
when retrieving a file uses Apple's Core Animation API. Upon its launch, Time Machine "floats" the active Finder or application window from the user's desktop to a backdrop depicting the user's blurred desktop wallpaper. Behind the current
active window A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment. They work in conjunc ...
are stacked windows, with each window representing a snapshot of how that folder or application looked on the given date and time in the past. When toggling through the previous snapshots, the stacked windows extend backwards, giving the impression of flying through a "time tunnel." While paging through these "windows from the past", a previous version of the data (or currently deleted data) may be retrieved.


Storage

Time Machine works with locally connected storage disks, which must be formatted in the APFS or
HFS+ HFS Plus or HFS+ (also known as Mac OS Extended or HFS Extended) is a journaling file system developed by Apple Inc. It replaced the Hierarchical File System (HFS) as the primary file system of Apple computers with the 1998 release of Mac OS 8 ...
volume formats. Support for backing up to APFS volumes was added with
macOS 11 Big Sur macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple Inc.'s operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the public ...
and since then APFS is the default volume format. Time Machine also works with remote storage media shared from other systems, including Time Capsule, via the network. When using remote storage, Time Machine uses sparse bundles. This acts as an isolation layer, which makes the storage neutral to the actual file system used by the network server, and also permits the replication of the backup from one storage medium to another. Sparse bundles are mounted by macOS like any other device, presenting their content as a HFS+ formatted volume, functionally similar to a local storage.


Requirements

Time Machine places strict requirements on the backup storage medium. The only officially supported configurations are: * A storage drive or partition connected directly to the computer, either internally or by a bus like USB or Thunderbolt and formatted as APFS or journaled
HFS+ HFS Plus or HFS+ (also known as Mac OS Extended or HFS Extended) is a journaling file system developed by Apple Inc. It replaced the Hierarchical File System (HFS) as the primary file system of Apple computers with the 1998 release of Mac OS 8 ...
. If the volume format is not correct, Time Machine will prompt the user to reformat it. * A folder on another Mac on the same network. * A drive shared by an Apple
Time Capsule A time capsule is a historic cache of goods or information, usually intended as a deliberate method of communication with future people, and to help future archaeologists, anthropologists, or historians. The preservation of holy relics dates ...
on the same network. * A drive connected to an Apple
AirPort Extreme The AirPort Extreme is a residential gateway combining the functions of a router, network switch, wireless access point and NAS as well as varied other functions, and one of Apple's former AirPort products. The latest model, the 6th generati ...
802.11ac model on the same network. (Earlier generations of the AirPort Extreme are not supported.) * Local network volumes connected using the Apple Filing Protocol or via an SMB3 share that advertises a number of capabilities. On a Time Capsule, the backup data is stored in an HFS+
disk image A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image i ...
and accessed via Apple Filing Protocol. Although it is not officially supported, users and manufacturers have also configured
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
and
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
servers and
network-attached storage Network-attached storage (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the tech ...
systems to serve Time Machine-enabled Macs. There are also a few software tools available on the market that can copy files inside Time Machine backups in Windows machines. Also see slowfranklin's comment and its replies. To add the guest UAM, add AFPD_UAMLIST="-U uams_guest.so" to the lobal/code> section in afp.conf.


Operation

Time Machine creates a folder on the designated Time Machine volume (local or inside a remote
sparse image A sparse image is a type of disk image file used on macOS that grows in size as the user adds data to the image, taking up only as much disk space as stored in it. Encrypted sparse image files are used to secure a user's home directory by the ...
) into which it copies the directory tree of all locally attached storage drives, except for files and directories that the user has specified to omit, including the Time Machine volume itself. Every hour thereafter, it creates a new subordinate folder and copies only files that have changed since the last backup and creates (in the case of HFS+ volumes)
hard link In computing, a hard link is a directory entry (in a directory-based file system) that associates a name with a file. Thus, each file must have at least one hard link. Creating additional hard links for a file makes the contents of that file ac ...
s to files that already exist on the backup drive. A user can browse the directory hierarchy of these copies as if browsing the primary disk. Some other backup utilities save deltas for file changes, much like version control systems. Such an approach permits more frequent backups of minor changes, but can often complicate the interaction with the backup volume. By contrast, it is possible to manually browse a Time Machine backup volume without using the Time Machine interface; Time Machine presents each backup to the user as a complete disk copy. Time Machine on HFS+ volumes creates multiple hard links to unmodified directories. Multiple linking of directories is a peculiar feature for HFS+, and is not supported on modern Unix file systems including Apple's own APFS. As a result, tools like rsync cannot be used to replicate a Time Machine volume; replication can only reliably be done by imaging the entire filesystem. Apple system events record when each directory is modified on the hard drive. This means that instead of examining every file's modification date when it is activated, Time Machine only needs to scan the directories that changed for files to copy. This differs from the approach taken by similar backup utilities rsync and FlyBack, which examine modification dates of all files during backup. Time Machine is also available in the
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
installation process. One of the features in the Migration Assistant interface is to restore the contents of a Time Machine backup. In other words, a hard drive can be restored from a Time Machine backup in the event of a catastrophic crash. OS X Mountain Lion introduced the ability to use multiple volumes simultaneously for Time Machine operations. When the user specifies more than one volume to use, macOS rotates among the desired volumes each time it does a backup.


Exclusion

Time Machine supports two forms of exclusion: one based on a user-configured list of paths (plus a set of system defaults), the other based on the extended file attribute . Since the attribute is applied to the file or directory directly, moving or copying will not affect the exclusion. The attribute should contain the string in any property list format. Writing instead sets the exclusion for iOS backups. Google Chrome is known to use the attribute to exclude its histories. Third-party backup applications that respect this setting include CrashPlan and Arq. Apple wraps the attribute into the command-line utility as well as a CoreServices API.


See also

* MobileMe Backup * List of backup software *
Version control In software engineering, version control (also known as revision control, source control, or source code management) is a class of systems responsible for managing changes to computer programs, documents, large web sites, or other collections o ...
*
AirPort Time Capsule The AirPort Time Capsule (originally named Time Capsule) is a wireless router which was sold by Apple Inc., featuring network-attached storage (NAS) and a residential gateway router, and is one of Apple's AirPort products. They are, essential ...
*Backup options built into Microsoft Windows:
System Restore System Restore is a feature in Microsoft Windows that allows the user to revert their computer's state (including system files, installed applications, Windows Registry, and system settings) to that of a previous point in time, which can be used ...
,
File History The transition from Windows 7 to Windows 8 introduced a number of new features across various aspects of the operating system. These include a greater focus on optimizing the operating system for touchscreen-based devices (such as tablet compute ...


References


External links


Apple Support: Back up your Mac with Time MachineMac OS X 10.5 Leopard review on Ars Technicabrief history of Time Machine and its evolution to using APFS
by Howard Oakley {{DEFAULTSORT:Time Machine (macOS) 2007 software MacOS-only software made by Apple Inc. Time Machine Backup software for macOS