Unveiling the Power of Intel 4004 CPU: Simulating its Intricate Architecture

Table of Contents

1. Introduction
2. What is the Intel 4004 CPU?
3. Architecture of the Intel 4004 CPU
   1. 4-bit architecture
   2. 4-bit bus
   3. Single chip integration
4. Memory and Input/Output (I/O) Support
   1. ROM (Read-Only Memory) chip
   2. RAM (Random Access Memory) chip
   3. Input and output ports
5. Internal Architecture of the Intel 4004 CPU
   1. Accumulator
   2. Registers
   3. Address stack
   4. Instruction set
6. CPU Simulation: CPU Only vs CPU with Support Chips
7. Simulation of the Intel 4004 CPU in Java
8. Conclusion
9. Resources

Simulating the Intel 4004 CPU: Unlocking the Power of the First Microprocessor

The Intel 4004 CPU is a landmark in the history of computer processors. It is widely recognized as the world's first microprocessor, integrating all essential components into a single chip. In this article, we will delve into the fascinating world of simulating the internal workings of the Intel 4004 CPU, exploring its architecture, memory and input/output support, internal organization, and different simulation approaches.

Introduction

Before we dive into the intricacies of simulating the Intel 4004 CPU, let's take a moment to understand its significance in the realm of microprocessors. While CPUs existed prior to the Intel 4004, they were implemented using multiple integrated circuits (ICs), with a separate CPU board combining these ICs to perform CPU functions. The Intel 4004, however, was a Game-changer as it integrated all the necessary components into a single chip. This groundbreaking innovation paved the way for the construction of modern computers.

What is the Intel 4004 CPU?

The Intel 4004 CPU made its debut in 1971 and boasts a 4-bit architecture. This means that data is internally stored in 4-bit registers and external communication occurs via a 4-bit bus. Surprisingly, there are only four pins dedicated to the transfer of addresses, instructions, and data. Despite its simplicity, the CPU supports 12-bit addresses, utilizing the four pins to send the address in three clock cycles. The maximum clock rate of the Intel 4004 CPU is a mere 740 kilohertz, a far cry from the multi-gigahertz speeds of modern processors.

Architecture of the Intel 4004 CPU

4-bit architecture

The Intel 4004 CPU's architecture revolves around its 4-bit design. The internal registers store data in 4-bit words, while the external bus operates at 4-bit capacity for data transfer. This compact architecture enables the CPU to fit into a single chip, a remarkable achievement for its time.

4-bit bus

With only four pins designated for address and data transfer, the 4-bit bus is the vital link between the Intel 4004 CPU and the external world. Despite its limited capacity, the CPU manages to support 12-bit addresses, employing clever techniques to transmit the address within the restricted pin count.

Single chip integration

The Intel 4004 CPU stands out as the first microprocessor due to its single-chip integration. While it required supporting ICs for certain functionalities, such as ROM (Read-Only Memory) and RAM (Random Access Memory), the fact that the CPU itself was a single chip marked a significant milestone in computer architecture.

Memory and Input/Output (I/O) Support

To comprehend the Intel 4004 CPU's operation, we must explore the memory and I/O support it offers.

ROM (Read-Only Memory) chip

The ROM chip plays a crucial role in the Intel 4004 CPU's functioning. Organized as 256 8-bit words (bytes), it stores instructions. As the name suggests, the ROM chip is read-only, meaning that it contains pre-determined instructions that the CPU fetches during program execution. Additionally, the ROM chip offers a 4-bit I/O port, further expanding the CPU's capabilities.

RAM (Random Access Memory) chip

Unlike the ROM chip, the RAM chip permits both reading and writing of data. A particular RAM chip, the 4002, contains 320 bits of memory, divided into four registers of 20 4-bit characters each. Among these registers, 16 are dedicated to main memory, while the remaining four serve as status registers. Additionally, the RAM chip features a 4-bit output port, enabling data transmission.

Input and output ports

The Intel 4004 CPU supports up to 16 4-bit input ports and 16 4-bit output ports. However, the absence of a dedicated signal for selecting an I/O port may seem puzzling. This discrepancy is resolved by employing additional ICs, such as the 4001 ROM chip and the 4002 RAM chip. These ICs provide the necessary support for I/O operations, effectively expanding the CPU's capabilities.

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