All computers share the same basic architecture, whether it is a mainframe or a Palm Pilot. All have memory, an I/O system, and arithmetic/logic unit, and a control unit. This type of architecture is named Von Neumann’s Architecture after the mathematician, John Von Neumann who conceived of the design. John Von Neumann begins his “Preliminary Discussion” with a broad description of the general-purpose computing machine containing four basic components. These are known as relating to arithmetic, memory, control, and connection with the human operator. In other words, the arithmetic/logical unit (ALU), the memory, the control unit (CU), and the input-output (I/O) devices that we see in the classical model of what a computer “looks like.
Computer Memory is the subsystem that serves as temporary storage for all program instructions and data that are being executed by the computer. It is typically called RAM (Random Access Memory). Memory is divided up into cells, each cell having a unique address so that the data can be fetched.
- Arithmetic/logical unit (ALU)
This subsystem is to perform all arithmetic operations and comparisons for equality. In the Von Neumann’s architecture, the arithmetic/logical unit (ALU) and the Control Unit (CU) are separate components, but in modern systems they are integrated into the processor. The ALU has 3 sections, the register, the ALU circuitry, and the pathways in between. The register is basically a storage cell that works like RAM and holds the results of the calculations. It is mush faster than RAM and is addresses differently. The ALU circuitry is that actually performs the calculations, and it is designed from AND, OR, and NOT gates just as any chip.
- Control Unit (CU)
The control unit is responsible for fetching the next program instruction to be run from memory, decode it to determine what needs to be done, and then issue the proper command to the ALU, memory and I/O controllers to get the job done. These steps are done continuously until the last line of a program is done, which is usually QUIT or STOP.
- Input-output (I/O) devices
This is the subsystem that allows the computer to interact with other devices and communicate to the outside world. It also is responsible for program storage, such as hard drive control.