RAMDISC Systems

RAMDISC 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 RAMDISC system can be an interesting solution. RAMDISCs reside in buffer cache, that is, they only will allocate the ammount of memory that is currently really in use. The only limitation is that the maximum capacity is defined at kernel/module compile time. The RAMDISC 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 specialities of Linux are related rather to the handling of the buffer chache, 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 RAMDISC based filesystem can operate very efficiently in respect to actually allocated RAM. To operate a RAMDISC system efficiently an appropriate filesystem must be chosen - there is no point in setting up a RAM-disc and then using reiserfs (atleast in most cases this will not be sensible) a slim filesystem like minixfs, allthough old will be quite suitable for such a setup and yeald and efficient use of resources (imposing minor restrictions with respect to maximum filename length and directory depth).