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Chapter 4. Memory > The RAM Disk

The RAM Disk

Another feature of the Memory control panel allows you to use a portion of main memory to create a RAM disk that is treated just like a hard drive (although it's much faster). Unless you have huge amounts of RAM installed, it can't substitute for a real hard drive; however, it can be useful in some situations, such as holding a Web browser's cache, which speeds up Web surfing. RAM disks on later Mac OS versions with modern Macs can retain their contents even when the computer is powered off. (The contents are written to the hard drive before shutting down and copied back when you start back up.) Remember that a RAM disk is not the safest place to put important files and documents—it's best used as fast temporary storage. Should your system freeze, the data in the RAM disk is more likely to be lost or corrupted than if it were stored on the hard drive. (A shareware utility called ramBunctious offers security options such as write-through to the hard drive that are not found in Apple's RAM disk. For more on ramBunctious, see below.)

To create a RAM disk, open the Memory control panel, and in the Ram Disk panel select the On radio button. Then adjust the slider or enter the size of the disk you'd like to create (Figure 4.6). If your Mac OS has the option, select the Save on Shut Down check box to preserve the RAM disk's contents even when the computer is powered down.

Figure 4.6. Open the Memory control panel to create a RAM disk.


When you move the slider (or type a number) to increase the RAM-disk size, the “Available built-in memory” number in the Virtual Memory panel and the Disk Cache figure are reduced. These reflect that the RAM disk is using memory that was available for the system. (In Mac OS 8.5 and later, the disk cache-size defaults to a percentage of available RAM.) Also note that the size of the RAM disk is reflected in the amount of memory the Mac OS is using when you select the About option in the Finder.

After you've selected the desired size and options, restart the Mac and you'll see the RAM-disk icon on the desktop. You use the RAM disk just as you would a normal drive except that it's noticeably faster. Dragging the RAM disk to the Trash has no effect; it can only be turned off from the Memory control panel. If the RAM disk contains any files, the options in the Memory control panel are grayed out and can't be changed. You must empty the contents or use the Finder's Erase Disk command before you can turn off the RAM disk.

The shareware RAM-disk utility ramBunctious ($25; www.clarkwoodsoftware.com/rambunctious/) has customizable options for speed, security, safety, and versatility. For instance, you can set it to write through to a file on a real disk for safety in the event of a crash. It also allows the simultaneous use of multiple RAM disks. Most notably, ramBunctious uses the same memory that applications use, so the memory is instantly available for other applications when the RAM disk is put away.


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