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Abstract

Ovonic unified memory (OUM) is an advanced memory technology that uses a chalcogenide alloy (GeSbTe).The alloy has two states: a high resistance amorphous state and a low resistance polycrystalline state. These states are used for the representation of reset and set states respectively. The performance and attributes of the memory make it an attractive alternative to flash memory and potentially competitive with the existing non volatile memory technology.















Review of memory basics

Every computer system contains a variety of devices to store the instructions and data required for its operation. These storage devices plus the algorithms needed to control or manage the stored information constitute the memory system of the computer. In general, it is desirable that processors should have immediate and interrupted access to memory, so the time required to transfer information between the processor and memory should be such that the processor can operate at, close to, its maximum speed. Unfortunately, memories that operate at speeds comparable to processors speed are very costly. It is not feasible to employ a single memory using just one type of technology. Instead the stored information is distributed in complex fashion over a variety of different memory units with very different physical characteristics.
The memory components of a computer can be subdivided into three main groups:

1) Internal processor memory: this usually comprises of a small set of high speed registers used as working registers for temporary storage of instructions and data.

2) Main memory: this is a relatively large fast memory used for program and data storage during computer operation. It is characterized by the fact that location in the main memory can be directly accessed by the CPU instruction set. The principal technologies used for main memory are semiconductor integrated circuits and ferrite cores.

3) Secondary memory: this is generally much larger in capacity but also much slower than main memory. It is used for storing system programs and large data files and the likes which are not continually required by the CPU;it also serves as an overflow memory when the capacity of the main memory when the capacity of the main memory is exceeded. Information in secondary storage is usually accessed directly via special programs that first transfer the required information to main memory. Representative technologies used for secondary memory are magnetic disks and tapes.

The major objective in designing any memory is to provide adequate storage capacity with an acceptable level of performance at a reasonable cost.