MAC times are pieces of file systemmetadata which record when certain events pertaining to a computer file occurred most recently. The events are usually described as 'modification' (the data in the file was modified), 'access' (some part of the file was read), and 'metadata change' (the file's permissions or ownership were modified), although the acronym is derived from the 'mtime', 'atime', and 'ctime' structures maintained by Unix file systems. Windows file systems do not update ctime when a file's metadata is changed[citation needed], instead using the field to record the time when a file was first created, known as 'creation time' or 'birth time'. Some other systems also record birth times for files, but there is no standard name for this metadata; ZFS, for example, stores birth time in a field called 'crtime'. MAC times are commonly used in computer forensics.[1][2] The name Mactime was originally coined by Dan Farmer, who wrote a tool with the same name.[3]
Modification time (mtime)[edit]
Feb 18, 2012 A Timeline of Mac OS For nearly 30 years, the Macintosh operating system has helped define desktop computing. With the announcement of OS X Mountain Lion, Apple is readying for its next evolution. 125 milliseconds A sample of the same scenario on OS X Mavericks: 125 milliseconds of timer execution with no user activity. Executing timers at the same time reduces power use by maximizing processor idle time. Conceptually this is done by applying a time window—based on the importance of each process—to every timer (see table below).
Mac Os Mojave
A file's modification time describes when the content of the file most recently changed. Because most file systems do not compare data written to a file with what is already there, if a program overwrites part of a file with the same data as previously existed in that location, the modification time will be updated even though the contents did not technically change.
Access time (atime)[edit]
A file's access time identifies when the file was most recently opened for reading. Access times are usually updated even if only a small portion of a large file is examined. A running program can maintain a file as 'open' for some time, so the time at which a file was opened may differ from the time data was most recently read from the file.
Because some computer configurations are much faster at reading data than at writing it, updating access times after every read operation can be very expensive. Some systems mitigate this cost by storing access times at a coarser granularity than other times; by rounding access times only to the nearest hour or day, a file which is read repeatedly in a short time frame will only need its access time updated once.[4] In Windows, this is addressed by waiting for up to an hour to flush updated access dates to the disk.[5]
Some systems also provide options to disable access time updating altogether. In Windows, starting with Vista, file access time updating is disabled by default.[6]
Change time and creation time (ctime)[edit]
Unix and Windows file systems interpret 'ctime' differently:
- Unix systems maintain the historical interpretation of ctime as being the time when certain file metadata, not its contents, were last changed, such as the file's permissions or owner (e.g. 'This file's metadata was changed on 05/05/02 12:15pm').
- Windows systems use ctime to mean 'creation time'[citation needed] (also called 'birth time') (e.g. 'This file was created on 05/05/02 12:15pm').
This difference in usage can lead to incorrect presentation of time metadata when a file created on a Windows system is accessed on a Unix system and vice versa.[citation needed] Most Unix file systems don't store the creation time, although some, such as HFS+, ZFS, and UFS2 do. NTFS stores both the creation time and the change time.
The semantics of creation times is the source of some controversy.[citation needed] One view is that creation times should refer to the actual content of a file: e.g. for a digital photo the creation time would note when the photo was taken or first stored on a computer. A different approach is for creation times to stand for when the file system object itself was created, e.g. when the photo file was last restored from a backup or moved from one disk to another.
Metadata issues[edit]
As with all file system metadata, user expectations about MAC times can be violated by programs which are not metadata-aware. Some file-copying utilities will explicitly set MAC times of the new copy to match those of the original file, while programs that simply create a new file, read the contents of the original, and write that data into the new copy, will produce new files whose times do not match those of the original.
Some programs, in an attempt to avoid losing data if a write operation is interrupted, avoid modifying existing files. Instead, the updated data is written to a new file, and the new file is moved to overwrite the original. This practice loses the original file metadata unless the program explicitly copies the metadata from the original file. Windows is not affected by this due to a workaround feature called File System Tunneling.[7]
See also[edit]
References[edit]
- ^Luque, Mark E. (2002). 'Logical Level Analyses of Linux Systems'. In Casey, E. (ed.). Handbook of Computer Crime Investigation: Forensic Tools and Technology. London: Academic Press. pp. 182–183. ISBN0-12-163103-6.
- ^Sheldon (2002). 'Forensic Analyses of Windows Systems'. In Casey, E. (ed.). Handbook of Computer Crime Investigation: Forensic Tools and Technology. London: Academic Press. pp. 134–135. ISBN0-12-163103-6.
- ^Dan Farmer (October 1, 2000). 'What Are MACtimes?'. Dr Dobb's Journal.
- ^'File Times'. Microsoft MSDN Library.
- ^'File Times'. Microsoft MSDN Library.
- ^'Disabling Last Access Time in Windows Vista to improve NTFS performance'. The Storage Team at Microsoft.
- ^'Windows NT Contains File System Tunneling Capabilities'. Microsoft Support.
Time Passed Mac Os 11
External links[edit]
- Discussion about Windows and Unix timestamps (Cygwin project mailing list)
What is Mac OS X 10.0?
Mac OS X is Apple's new operating system. I've said it before and I'll say it again: the 'X' is pronounced 'ten', like the roman number, not 'ex' like the letter. Don't make me come over there.
Mac OS X was released on March 24th, 2001, with a suggested retail price of $129 and a version number of 10.0. Don't let the version number confuse you; this is the first official release of Apple's new OS. It was preceded by many developer releases and one public beta release.
To say that Mac OS X has been eagerly awaited by Mac users is an understatement. Apple has been trying to produce a successor to the classic Mac OS operating system for almost 15 years. It's a tragicomic litany of code names: Pink, Taligent, Copland, Rhapsody. In the early days (the Pink project was launched in 1987), Mac users paid little attention to these efforts, confident that their current OS was the most advanced in the personal computer market. But as the years passed and competing operating systems evolved, both by adopting Mac-like GUIs and by advancing their core OS features, Mac users--as well as Apple itself--became skittish.
By 1995, Windows had confined Apple's OS to a small corner of the market. Perhaps Windows 95 wasn't 'insanely great', but the market had declared that it was 'good enough.' Meanwhile, Microsoft quietly continued its own long-running project to radically revise its core operating system technologies: Windows NT (which eventually gave birth to Windows 2000, and soon, Windows XP).
By the time Apple's penultimate next generation OS project, Copland, was mercifully killed in 1996, the situation was dire. Mac users had suffered too many broken promises, and Apple had stumbled down too many blind alleys. By all rights, Copland should have been Apple's last chance. But the acquisition of NeXT and the second coming of Steve Jobs gave Apple one final window of opportunity.
AdvertisementDespite the (comparatively) minor market requirements hiccup of the Rhapsody strategy, the Mac OS X project proceeded with what can only be described as single-minded determination, from its official announcement in May of 1998 to its first release in March of 2001. Dates were missed, features were added and removed, but unlike all earlier efforts, this one produced a shipping product.
And yet the success of Mac OS X is still an open question. Unlike the relatively controlled public image of the Copland project, Mac OS X has endured the increased scrutiny of the Internet age. While Mac users from 1994 to 1996 were treated to optimistic articles and future-world mock-ups in enthusiast publications like Macworld and MacUser magazine, Mac OS X has been analyzed by amuchwideraudience.
Mac Os Versions
Here at Ars Technica, we've been following Mac OS X since its second developer release. It may seem strange to have seven articles dedicated to a product before the first official release, but the journey of Mac OS X has certainly been an interesting one.
Mac Os Catalina
This article will cover Mac OS X 10.0, but it will build on everything that was discussed in the earlier articles. If you haven't already read them (or similar articles elsewhere), you may have some difficulty following along. The list of earlier OS X articles appears below in reverse-chronological order. The most relevant are the two most recent: the Public Beta article and the relevant section of my recent Macworld San Francisco coverage.
- MWSF: Mac OS X Post-Beta 1/17/2001
- Mac OS X Public Beta 10/03/2000
- Mac OS X Q & A 6/20/2000
- Mac OS X DP4 5/24/2000
- Mac OS X DP3: Trial by Water 2/28/2000
- Mac OS X Update: Quartz & Aqua 1/17/2000
- Mac OS X DP2: A Preview 12/14/1999
Let's begin...