Module 1: introduction to organization and architecture of computer  (Page 3/4)

• Central Processing Unit (CPU): Controls the operation of the computer and performs its data processing functions. Often simply referred to as processor.
• Main Memory: Stores data.
• I/O: Moves data between the computer and its external environment.
• System Interconnection: Some mechanism that provides for communication among CPU, main memory, and I/O.

There may be one or more of each of the above components. Traditionally, there has been just a single CPU. In recent years, there has been increasing use of multiple processors, in a single system. Each of these components will be examined in some detail in later lectures. However, for our purpose, the most interesting and in some ways the most complex component is the CPU; its structure is depicted in [link] . Its major structural components are:

• Control Unit (CU): Controls the operation of the CPU and hence the computer.
• Arithmetic and Logic Unit (ALU): Performs computer’s data processing functions.
• Register: Provides storage internal to the CPU.
• CPU Interconnection: Some mechanism that provides for communication among the control unit, ALU, and register.

Each of these components will be examined in some detail in next lectures.

Brief history of computers

The first generation: vacuum tubes

• ENIAC

The ENIAC (Electronic Numerical Integrator And Computer), designed by and constructed under the supervision of Jonh Mauchly and John Presper Eckert at the University of Pennsylvania, was the world’s first general-purpose electronic digital computer. The project was a response to U.S. wartime needs. Mauchly, a professor of electrical engineering at the University of Pennsylvania and Eckert, one of his graduate students, proposed to build a general-purpose computer using vacuum tubes. In 1943, this proposal was accepted by the Army, and work began on the ENIAC. The resulting machine was enormous, weighting 30 tons, occupying 15,000 square feet of floor space, and containing more than 18,000 vacuum tubes. When operating, it consumed 140 kilowatts of power. It was aloes substantially faster than any electronic-mechanical computer, being capable of 5000 additions per second.

The ENIAC was decimal rather than a binary machine. That is, numbers were represented in decimal form and arithmetic was performed in the decimal system. Its memory consisted of 20 “accumulators”, each capable of holding a 10-digit decimal number. Each digit was represented by a ring of 10 vacuum tubes. At any time, only one vacuum tube was in the ON state, representing one of the 10 digits. The major drawback of the ENIAC was that it had to be programmed manually by setting switches and plugging and unplugging cables.

The ENIAC was completed in 1946, too late to be used in the war effort. Instead, its first task was to perform a series of complex calculations that were used to help determine the feasibility of the H-bomb. The ENIAC continued to be used until 1955.

• The von Neumann Machine

As was mentioned, the task of entering and altering programs for the ENIAC was extremely tedious. The programming process could be facilitated if the program could be represented in a form suitable for storing in memory alongside the data. Then, a computer could get its instructions by reading them from memory, and a program could be set of altered by setting the values of a portion of memory.