Dynamically allocable RAM disk

DETAILED DESCRIPTION OF THE INVENTION FIG.
1 shows a memory management system 10 used in the present invention.
A processor 15 communicates with a filesystem 20 and a memory manager 25.
Memory manager 25 allocates random access memory (RAM) 30 between processor 15 and filesystem 20.
Dynamic RAM disk device driver 35 communicates with filesystem 20 and memory manager 25 to construct and maintain dynamic RAM disk 40.
Dynamic RAM disk 40 is formed from clusters of RAM 30.
Dynamic RAM clusters 40 need not be contiguous in RAM 30.
Dynamic RAM disk 40 operates by allocating system memory 30 to accommodate the storage of data by filesystem 20.
Subsequent calls from filesystem 20 to read or write data result in information being copied between filesystem 20 buffers and dynamic RAM disk 40 memory space.
The address in dynamic RAM disk 40 memory space is computed based on a cluster and sector offset scheme.
Filesystem 20 operates on logical blocks.
Dynamic RAM disk 40 maps logical blocks to physical clusters and sectors by dividing the logical block value by the number of sectors per cluster.
In a typical application, the number of sectors per cluster is 16.
The integer value of the quotient is the number of the physical cluster and the remainder is the number of the physical sector.
Dynamic RAM disk 40 allocates memory 30 as needed to store data, leaving more memory available to other subsystems for use.
As files are deleted from filesystem 20, dynamic RAM disk 40 is informed of sectors that are discarded.
When all of the sectors in a cluster have been discarded, the cluster is released and memory 30 is returned to the system.
Sectors are marked as active or inactive using a sector freelist.
The sector freelist is an array of bits, where each bit corresponds to a sector in the associated cluster.
If a bit in the freelist is set, the corresponding sector is active.
When all bits in the freelist are clear, the associated cluster may be safely deallocated and returned to the system for other uses.
Where supported by memory manager 25, each cluster may be relocated to reduce fragmentation problems in systems where there is a high frequency of file creation and deletion