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Solved: Lr 6.14 just gave me a pop up saying it will not be compatible with future versions of Mac OS X. (I am currently running Mohave 10.14.1.) I paid for - 10247152. The 'X' in Mac OS X and OS X is the Roman numeral for the number 10 and is pronounced as such. The X was a prominent part of the operating system's brand identity and marketing in its early years, but gradually receded in prominence since the release of Snow Leopard in 2009. UNIX 03 certification was achieved for the Intel version of Mac OS X.

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What's the big deal about operating systems in the first place? What do they actually do? An operating system is the level of programming that lets you do things with your computer. The operating system interacts with a computer's hardware on a basic level, transmitting your commands into language the hardware can interpret. The OS acts as a platform for all other applications on your machine. Without it, your computer would just be a paperweight.

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At its heart, a computer is a number-crunching device. It takes input in the form of zeros and ones -- bits -- and channels them through various circuits and processors. The hardware behaves according to strict rules. We define these rules using things like logic gates, which take input and produce an output in a predictable way. Some simple computers have no need of an operating system because they only perform a specific task. But personal computers need to be more versatile. The operating system allows complex programs to access the capabilities of the hardware to get results. Only the hardware's physical properties and our own imaginations can limit what programs can do.

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You could design an operating system by physically programming it into a computer's circuits. This would require building electrical pathways using millions of logic gates. But such an operating system would be inflexible. That's why operating systems like Mac OS X and Windows are software. Software is more malleable than hardware -- you can make changes through software patches and version updates. To do the same with hardware would mean switching out physical chips and circuit boards.

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Operating systems are like the manager for a computer. It's the job of the OS to monitor what software needs and what the hardware can provide. As you run applications on your computer, the OS allocates the resources necessary to complete the task. That can include processing power, memory allocation and computer storage access, among other things. Ideally, the OS will make sure that your computer's hardware is never overtaxed.

The OS also allows programs to run on a computer. Without an OS, a programmer would have to design an application to run on the hardware directly. This isn't very efficient. An operating system acts as an application interface to the hardware. The OS does this through an application program interface (API). Program developers build applications for the API. Assuming the programmer has done a good job at building an application without any serious bugs, it should run just fine on the operating system.

One important part of the Mac computer is the firmware. Firmware is a level of programming that exists directly on top of a hardware layer. It's not part of the operating system itself. The Mac firmware is the first stored program that executes when you turn on a Mac computer. Its job is to check the computer's CPU, memory, disk drives and ports for errors. The PC equivalent to the Mac firmware is called BIOS, which stands for basic input-output systems. A second program called a bootloader loads the Mac OS X, assuming there are no errors reported by the firmware.

Next, we'll take a closer look at what makes the Mac OS X tick.

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]

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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]

  1. ^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.
  2. ^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.
  3. ^Dan Farmer (October 1, 2000). 'What Are MACtimes?'. Dr Dobb's Journal.
  4. ^'File Times'. Microsoft MSDN Library.
  5. ^'File Times'. Microsoft MSDN Library.
  6. ^'Disabling Last Access Time in Windows Vista to improve NTFS performance'. The Storage Team at Microsoft.
  7. ^'Windows NT Contains File System Tunneling Capabilities'. Microsoft Support.

External links[edit]

  • Discussion about Windows and Unix timestamps (Cygwin project mailing list)

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