Content-addressable (associative) memory devices

DETAILED DESCRIPTION According to one aspect of the present invention there is provided a compound associative memory for use with a data-parallel computer, the memory comprising: a bit-parallel word-organised associative memory comprising an array of associative memory cells arranged to be capable of bit-parallel search and write operations; a bit-serial associative memory comprising an array of memory cells arranged to be capable of bit-serial search and write operations, but not word bit-parallel search and write operations; wherein the bit-serial memory is operatively connected to the bit-parallel memory and arranged to operated as an extension of the same.
The present invention is able to overcome the problems of the prior art as it is possible to write to specific bits of a data word in the compound associative memory whilst still retaining the ability to carry out data-parallel data searches.
The new associative memory architecture of the present invention, in one embodiment, utilises a conventional three-transistor pseudo-static RAM circuit to provide a very dense memory to augment a 10 transistor pseudo-static CAM cell of a type already used in the inventors' ASP technology.
As mentioned above, the compound memory essentially comprises two banks, one of fully associative (word-organised) content-addressable memory, and the other of bit-serial associative memory.
This latter memory bank is referred to as extended memory.
In an exemplary embodiment, the two banks share common match lines and common write lines which enables them to function in a unified manner.
This compound memory as a whole is restricted to operations of a bit-serial nature (i.
e.
it is incapable of sustaining word-organised (bit-parallel) search or write operation).
However, the bank of fully associative (word-organised) content-addressable memory retains this capability.
The restriction to bit serial memory enables the construction of the extended memory to be simplified there by reducing cost, complexity and power consumption