Abstract :
As system speed requirements increase, designers often find it to their advantage to go beyond the use of traditional design alternatives, using devices which have previously been unavailable. One of the newer breed of ICs which help boost system performance is the specialty memory. These memories incorporate new functions and features to simplify the design of extremely high performance systems. One of the fastest blossoming fields of specialty memories is specialty static RAMs. This is mostly due to the fact that static RAMs have always been used in high speed cache and graphics processor design, a trend which has forced SRAM manufacturers to strive to provide the fastest speed devices possible. The speed of these devices is often augmented by the addition of simple logic functions, which can be implemented on the memory chip itself at a delay penalty of only about 0.5 to 2.0ns. By doing this, the speed of any critical path which contains a static RAM can be considerably improved. Another, more unusual approach is to perform changes to the actual static RAM array itself. This approach is more costly, but can add benefits which can be achieved no other way. Examples of such architectures include dual-ported cells, which are used in FlFOs as well as dual-port RAMs, and content-addressable memories (CAMs) which are usually implemented in lookup tables within virtual memory management units (MMUs). A newer device, which has only been available for about a year is the FourPort memory, a device which allows simultaneous 25ns random access to the same emeory array from four independent ports.
