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How OS X Manages Data

Memory Management in Mac OS
The earlier versions of Mac used a handle-based approach to allocate and deallocate memory. In this memory allocation technique, a relocatable handle was the center stage of the whole process. This handle was basically an abstraction of reference to the memory. It facilitated the movement of actual data referred without invalidating the handle. The handle pointed to the table known as ‘master pointer block’ that contained pointers to the actual data. When there was a need to compact memory, this table was updated after the process finished execution. Two machine areas were used to implement this scheme- the system heap (for OS) and the application heap. As the application heap dissolved after quitting the application, fragmentation was reduced to some extent. However, the Mac machines continued to run slowly and other problems persisted.

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How OS X Manages Data
With OS X’s HFS+, Apple introduced a range of built-in safeguards to address the fragmentation issues and breathe a new life into your Mac machines. The following key points will highlight some of the major changes brought to the Mac OS X by the new HFS+ file system:

  • HFS+ improves memory allocation scheme by preventing use of recently freed file space on your Mac hard drive. Alternatively, it searches for large portions of free space available on the drive and uses this space to store large files in contiguous memory locations. This helps to prevent fragmentation of the drive.
  • OS X is equipped to combine various small allocations into one larger allocation on the drive. The process automatically defragments files and helps to minimize file system fragmentation.
  • A technique known as ‘Hot File Adaptive Clustering’ keeps track of all your frequently-accessed and read-only files and places them to a special region on the drive called ‘Hot Zone’. The process involves defragmenting files during the transfer. Hot Zone, where your frequently-accessed files are placed, has the fastest access.
  • OS X also defragments highly fragmented files on-the-fly that contain more than 8 fragments. These files are automatically defragmented when they are opened on your Mac machine.

With this optimized data management in Mac OS X, you can rest assured that your Mac is less likely to slow down to a crawl. However, as the drive fills up, same problems may appear.

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