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Memory compression brings RAM Doubler to OS X Mavericks

A new feature in Apple's upcoming OS X is reminiscent of a past technology for enhancing RAM use in Macs.

Today at the World Wide Developer Conference keynote, Apple announced a new feature in the upcoming OS X Mavericks that is reminiscent of the RAM Doubler technology available for classic Mac systems in the '90s.

In the mid-'90s, Mac systems came with 8MB to 32MB RAM, and as has always been the case, greater application usage required more RAM.

Overcoming RAM restrictions required you either purchase more RAM, or enable and expand virtual memory usage in the system's control panel to make use of the hard drive as a location for RAM contents. Unfortunately these features were either expensive or resulted in great slowdowns, as is often the case with virtual memory usage.

Memory usage in OS X
High memory usage will constrain Free Memory (green), and result in the system slowing down as memory contents is stored on the hard drive. Screenshot by Topher Kessler/CNET

To combat this, a software company called Connectix (original developers of the popular Virtual PC emulator) released a memory management tool called RAM Doubler, that compressed working memory and prevented the need for relying solely on expanding virtual memory through hard drive usage.

By compressing memory, RAM Doubler offered an intermediately performing alternative between the hard drive and true RAM, for expanding the overall RAM available to programs. This technology could effectively double the available memory for programs without needing to buy more RAM.

As memory management in the Mac OS developed and OS X debuted, the utility of RAM Doubler fell off.

However, in today's preview of the upcoming OS X Mavericks at WWDC, Apple announced a new memory management feature that brings aspects of RAM Doubler back to the Mac OS.

Currently OS X establishes a memory footprint that holds contents even for programs that are currently open but not active, so as you open more programs available memory will become less and less, even if the programs are idling and not being used.

Memory compression diagram
Memory compression reduces the size of inactive memory contents, allowing more items to run at once. Apple

In OS X Mavericks, Apple has implemented memory compression features that, like RAM Doubler, compresses the RAM used by inactive programs so the overall memory footprint of a given set of open applications can be far less.

The memory compression works by a dictionary-based WKdm algorithm, and utilizes multiple cores of the system's CPU to shrink the memory usage of inactive applications by more than 50 percent.

This should allow you to get more done without the system resorting to as much memory paging, where it writes memory contents to disk in order to free up RAM for other uses.

What can Mac users expect from memory compression? Overall, this new feature should allow you to get more done without needing to upgrade your RAM. If you currently have only 4GB RAM installed on your system, then you may find your system begin to crawl if you open a large document while you have other applications running. In these situations, checking Activity Monitor will show the "Free Memory" amount as a minimum of your installed RAM.

Currently the only way to currently free this memory is to quit applications and close documents. With memory compression, the system should make more free memory available to extend your system's abilities a bit more before you experience significant slowdowns.

This feature joins others like Sudden Termination that Apple includes in OS X to help manage constrained memory resources. While the best solution for a system with limited memory is to purchase more RAM, memory compression will give the system a little more breathing room.

This development will also be good news for systems such as the MacBook Air and MacBook Pro, which have fixed amounts of RAM.

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