RAMDISC Systems

RAMDISK systems are not Linux specific, but the implementation under Linux is quite flexible and for many embedded systems that have very slow ROM or media with a relatively low permissible number of read/write-cycles, a RAMDISK system can be an interesting solution. RAMDISKs reside in buffer cache, that is, they only will allocate the amount of memory that is currently really in use. The only limitation is that the maximum capacity is defined at kernel/module compile time. The RAMDISK itself behaves like a regular block-device; it can be formatted for any of the Linux filesystems and populated like any other block oriented storage device. The specialties of Linux are related rather to the handling of the buffer cache, which is a very efficiently managed resource in the Linux kernel. Buffers are allocated on demand and freed only when the amount of free memory in the system drops below a defined level - this way the RAMDISK based filesystem can operate very efficiently in respect to actually allocated RAM. To operate a RAMDISK system efficiently an appropriate filesystem must be chosen - there is no point in setting up a RAM-disc and then using reiserfs (at least in most cases this will not be sensible) a slim filesystem like minixfs, although old will be quite suitable for such a setup and yeld and efficient use of resources (imposing minor restrictions with respect to maximum filename length and directory depth).