Technical Description of an Intel 4004 Central Processing Unit (CPU)

CCNY – ENGL-217

Prof. Davidow

David A. A. Balaban – 23572639

Outline:

1. Introduction
2. Body
   • Arithmetic Logic Unit (ALU)
   • Control Unit (CU)
   • Memory Unit
3. Glossary
4. References

Intro:

In 1936, Dr. Alan Turing was about to give birth to the first general purpose computer ever, that broke the German Nazi code “Enigma”, the Turing Machine.  According to Imperial War Museum, Enigma was a type of enciphering machine used by the German armed forces to send messages securely. The Turing machine was the first general purpose computer composed of switches, relays and vacuum tubes, components that allowed Dr. Turing’s invention to perform arithmetic and logic operations at an incredible speed, which broke the German Nazi code, helping the British stay one step ahead.

Since Dr. Turing’s machine, the general-purpose computer was a goal to be achieved by every nation that wanted to stay ahead. The processing power that a computer introduces disbalances the natural order of things, making complex calculations to be done by anyone and with incredible speed.

After the general-purpose computer was improved, came the next task. Creating a personal general-purpose computer, that every American could have one day. Up until then computers took up big rooms and required not only a huge space, but also a huge investment. There was a race to make computer accessible to everyone and everywhere. That’s where the Intel 4004 CPU comes in, “a ‘building block’ that engineers could purchase and then customize with software to perform different functions in a wide variety of electronic devices.” (The Story of the Intel® 4004).

Believed to be the first personal general-purpose CPU, intel’s 4004 chip started the computer revolution, by making it accessible to anyone, anywhere. Now, the consumer does not have to spend millions of dollars to have their own personal computer.

Body:

The Central Processing Unit (CPU) is the computer’s primary component for processing instructions. Every device that does computation has a CPU. It’s where the Operational System (OS) and applications run. There are 4 parts to a CPU: the Arithmetic Logic Unit (ALU), the Control Unit (CU), and its memory. The CPU itself is normally a square chip with multiple metallic connectors (or pins) on the underside, and it’s inserted in the CPU socket on the motherboard.

Intel’s 4004 CPU is a 4-bit microprocessor in a rectangular shape and 16 pins, as shown on Figure 1. The 4004 is called 4-bit because it has 4 bit registers, but the CPU can directly address 8-bit instructions and 5120 bits of RAM memory. The processor performs using 5.5 volts of input at a maximum clock speed of 740 kHz.

Every instruction is 8-bits long and is divided into two 4-bit parts. The upper 4-bits are the OPR field, containing the operation code, the lower 4-bits are the OPA field, containing the modifier for such instruction. It takes one cycle to read an 8-bits long instruction. There are 46 instructions for the intel 4004 chip.

In addition, the 4004 easily interfaces with keyboards, displays, printers and other peripheral equipment.

1. Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit is responsible for every arithmetic and logic operation. It’s where the CPU will perform every calculation and logic tests. It represents the fundamental building block of the CPU. The ALU works by fetching binary numbers from registers and performing any algebraic operations to it, that might be either plain arithmetic, as seen on figure 2, or logic operations, as seen on figure 3.

• Control Unit (CU)

The control unit is the processor component that relates every instruction that goes in the processor to the computer. It tells the computer’s memory, ALU, and input and output devices how to respond to the instructions that have been sent to the processor. It does so by providing timing and control signals, it literally directs the flow of data between the CPU and other devices or components.

Normally, the CU is the first unit of the CPU to receive an instruction. It takes that instruction and decodes it into several sequential steps that controls and coordinates the CPU’s other units to properly manipulate the data

• Memory

Finally, the memory unit is probably one of the most important units within a CPU. The memory unit stores instructions, data and intermediate results. Also known as RAM, its size affects the speed, power, and capability of a CPU. It uses stack memory to store information and all of the data is in binary, while every address is in hexadecimal.

The memory of a CPU can be divided into the RAM and the Caches. The RAM is the general purpose memory, that will store data, instructions and intermediate results, the RAM will clear out once the system is turned off, in other words, it won’t store information after a system reboots. The caches are a special partition of memory that have a specific purpose, the caches can also be called Registers. The registers on the 4004 chip are all 4-bit long registers and the 4004 chip have only the utmost basic registers: the accumulator, data registers, pointers and counting registers.

Glossary:

Binary: Number system of base 2

Hexadecimal: Number system of base 16

BIT: Binary Digit, is a digit in the binary number system

BYTE: An array of 8 bits

RAM: Random Access Memory, is a type of memory that can be accessed randomly, that is a byte can accessed without touching preceding bytes. It’s where the computer does most of its calculations and operations.

ROM: Read-Only Memory, is a type of memory that can only be read and not written, most programs and applications are stored here then called into the RAM when running

Operational System: The program that manages every other program and file in the computer.

Boolean Logic: A form of algebra centered in the logic operations AND, OR and NOT

Registers: A special partition of the CPU’s memory, dedicated for specific tasks

Stack Memory:  Memory where data is added or removed in a last-in-first-out fashion. A good way of picturing is to imagine a stack of folders, where the bottom folder is only accessible if every other folder on top of it is removed

References:

Arora, Manish, et al. “Redefining the Role of the CPU in the Era of CPU-GPU Integration.” IEEE Micro, vol. 32, no. 6, 2012, pp. 4–16., doi:10.1109/mm.2012.57

Beal, Vangie. “CPU – Central Processing Unit.” Router vs Switch vs Hub: What’s the Difference? Webopedia, www.webopedia.com/TERM/C/CPU.html

“CPU.” P2P (Peer To Peer) Definition, techterms.com/definition/cpu

Fisher, Tim. “What Does a CPU Do? Learn More About CPU Cores, Clock Speed, and More.” Lifewire, Lifewire, 8 Feb. 2019, www.lifewire.com/what-is-a-cpu-2618150

“Intel® Core™ Processors Technical Resources.” Intel, www.intel.com/content/www/us/en/products/docs/processors/core/core-technical-resources.html

“The Story of the Intel® 4004.” Intel, www.intel.com/content/www/us/en/history/museum-story-of-intel-4004.html

Kumar, A. “The HP PA-8000 RISC CPU.” IEEE Micro, vol. 17, no. 2, 1997, pp. 27–32., doi:10.1109/40.592310.

Safford, Matt. “How to Buy the Right CPU: A Guide for 2019.” Tom’s Hardware, Tom’s Hardware, 26 Feb. 2019, www.tomshardware.com/reviews/cpu-buying-guide,5643.html

“Computer Processor History.” Computer Hope, 16 Dec. 2018, www.computerhope.com/history/processor.html

“The Microprocessor.” History of Computers and Computing, Birth of the Modern Computer, Electronic Computer, Manchester Small Scale Experimental Machine, www.history-computer.com/ModernComputer/Basis/microprocessor.html

“How Alan Turing Cracked The Enigma Code.” Imperial War Museums, 5 Jan. 2018, www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code