the von neumann model

The Von Neumann Model.
John von Neumann, along with others, proposed the concept of the stored program that we use even today. The idea was to keep a program in the memory and read the instructions from it. He also proposed an architecture that clearly identified the components we have presented previously: ALU, control, input, output, and memory as illustrated in Figure 1. This architecture is known as the von Neumann architecture.











This architecture uses what is known as the stored program model. In the von Neumann architecture, the stored program is the most important aspect of the von Neumann model. The key features of this architecture are as follows:
• There is no distinction between instructions and data. This requirement has several main implications:
1. Instructions are represented as numbers, just like the data themselves. This uniform treatment of instructions and data simplifies the design of memory and software.
2. Instructions and data are not stored in separate memories; a single memory is used for both. Thus, a single path from the memory can carry both data and instructions.
3. The memory is addressed by location, regardless of the type of data at that location.

• By default, instructions are executed in the sequential manner in which they are present in the stored program.
A program is stored in the computer’s memory along with the data to be processed (A computer with a von Neumann architecture has a single memory space that contains both the instructions and the data, see figure 2). This can lead to a condition called the von Neumann bottleneck, it places a limitation on how fast the processor can run. Instructions and data must share the same path to the CPU from memory, so if the CPU is writing a data value out to memory, it cannot fetch the next instruction to be executed. It must wait until the data has been written before proceeding and vice versa.