How does Apollo AGC core memory work?

In the midst of the Space Race, a groundbreaking technology emerged aboard the Apollo missions, epitomizing the meld of innovation and necessity.

The Apollo Guidance Computer (AGC) was the linchpin of moon landings, with its core memory being the heartbeat of operations. Discover the intricacies of the AGC core memory, the marvel of engineering that transcended earthly bounds, propelling humanity to the lunar surface.

Through a delve into its historical roots, architectural finesse, and operational brilliance, unravel the essence of this pivotal technology that etched a mark in space exploration chronicles.

Step-by-Step Guide to Apollo AGC Core Memory Functioning

Core Magnetization:
- A current is sent through a wire passing through a ferrite core.
- The core gets magnetized in a specific direction if the current exceeds a certain threshold.
Reading Data:
- A current in the opposite direction is sent to read the data.
- This action induces a voltage pulse in the ‘sense wire,’ identifying the core’s magnetization direction, thus interpreting the stored bit.
Destructive Reading:
- Reading is destructive; the original magnetization state is altered.
Data Restoration:
- Post-reading, a restoration cycle reinstates the original magnetization state, ensuring data integrity.
Writing Data:
- The ‘write’ wire is utilized to magnetize the core in the desired direction, representing a binary 0 or 1.
Addressing Cores:
- Core memory is organized in a planar matrix, allowing for specific core addressing for reading or writing operations.
Sophisticated Access:
- Stacking planar matrices creates a 3D structure.
- Sophisticated access schemes are employed, threading cores in each plane with up to 5 wires for precise data access and manipulation.

Exploring Apollo AGC Core Memory Features

This illustration explains the concept of core rope memory. Imagine the data displayed above the cores in the image needs to be stored in the designated core. For instance, to store the value "1000" in the first core on the left, you would connect the top wire from the selection circuit to the core while letting the subsequent three wires skip or bypass that core. When this specific core is read, the connected wire signifies a "one" because all cores in the rope are permanently set to represent ones, whereas the wires that bypass the core will represent zeroes. — This illustration explains the concept of core rope memory. Imagine the data displayed above the cores in the image needs to be stored in the designated core. For instance, to store the value “1000” in the first core on the left, you would connect the top wire from the selection circuit to the core while letting the subsequent three wires skip or bypass that core. When this specific core is read, the connected wire signifies a “one” because all cores in the rope are permanently set to represent ones, whereas the wires that bypass the core will represent zeroes.

Key Takeaways
– Core memory was a prominent memory technology, using ferrite cores magnetized in two directions to store data bits.
– Invented in 1949, core memory was first utilized in the Whirlwind computer and later commercialized by IBM in 1955.
– Apollo Guidance Computer (AGC) employed core memory due to its reliability, radiation resistance, and non-volatile nature.

Historical Context of Apollo AGC Core Memory

The core memory technology emerged in the late 1940s. Photo of a Caucasian man in his 40s, dressed in a brown suit and wearing glasses, looking intently at a computer from the 1950s, which has large panels and dials. The ambiance is filled with a hum from the machine. Old technical manuals and diagrams are spread out on a nearby desk.

The core memory technology emerged in the late 1940s, bringing a significant leap in the cost-effectiveness and reliability of computer memory systems.

This innovative memory solution came as an alternative to the then-utilized mercury and nickel-wire delay lines, magnetic drums, and Williams tubes.

The invention of core memory is largely credited to A. Wang and J.W. Forrester. Core memory found its first application in the Whirlwind computer, marking the beginning of a new era in-memory technology.

Year	Milestone
1949	Invention of Core Memory
1955	Commercialization by IBM
1974	Transition to Semiconductor Memory

Photo of a Caucasian man in his 40s, dressed in a brown suit and wearing glasses, looking intently at a computer from the 1950s. The machine has large panels, dials, and a series of cables connected to it. The ambiance is filled with a hum from the machine. Old technical manuals, blueprints, and diagrams are spread out on a nearby wooden desk, showcasing the intricate details of the computer's design.

Core memory was widely adopted in commercial computers, with the IBM 705 being the first to be equipped with a core memory of 100,000 bits, boasting a cycle time of 17 μs.

The price per bit of core memory was 20 cents in 1960, which saw a steady decrease of 19% per year, making it an economical choice for computer manufacturers.

By 1976, a staggering 95% of all computer main memories were made of ferrite cores, with 20-30 billion produced globally on a yearly basis.

Central Role of Core Memory in Apollo AGC

How was the Apollo Guidance Computer (AGC) Tested Before the Mission?

The Apollo Guidance Computer (AGC) utilized core memory technology due to its exceptional traits:

Non-volatility: Retained information even when power was switched off.
Radiation Resistance: Withstood the harsh space radiation environment.
Reliability: Offered a dependable memory solution for critical space missions.

The core memory in Apollo AGC comprised small ferrite rings, also known as cores. These cores could be magnetized in either of two opposite directions (clockwise or counterclockwise), representing a binary digit or bit (0 or 1).

Core Memory Architecture

Core memory was organized in a 3D matrix configuration, facilitating sophisticated access schemes that were crucial for the efficient operation of the Apollo AGC. Each core was interlaced with wires that controlled the reading, writing, and sensing operations.

Writing: A current passing through the wires magnetized the core in a specific direction.
Reading: The process of reading was destructive, requiring a restoration cycle to reset the magnetized state.

The unique architecture and operational principles of core memory made it an invaluable component of the Apollo AGC, playing a pivotal role in the successful moon landing missions.

Transition to Modern Memory Technologies

The advent of semiconductor (transistor) memory with the 4 kbit chip in 1974 marked the beginning of a transition from core memory to more advanced memory technologies.

Despite this shift, core memory’s legacy lived on, setting the groundwork for modern memory systems that propelled further advancements in computing technology and space exploration.

Operational Mechanics of Apollo AGC Core Memory

The essence of core memory lies in the persistent magnetization of a ferrite core by a current exceeding a threshold. This magnetization is reversible, with a current in the opposite direction.

The process induces a voltage pulse in another wire, the ‘sense wire,’ with the pulse’s polarity determined by the initial magnetization direction. Reading is a destructive operation, necessitating a restoration cycle.

Matrix Configuration

Core memories were typically arranged in a planar matrix, with the ‘write’ wire divided into two (row, column), each bearing half the threshold switching current.

This allowed for addressing a specific core for reading or writing. Stacking such planar matrices created a 3D structure, enabling sophisticated access schemes with up to 5 wires threading the cores in each plane.

Mechanization of Core Threading

Early core memory was hand-woven a laborious, costly process. However, mechanization drastically cut down the time to thread a 64*64 plane from 25 hours to a mere 12 minutes, marking a significant stride in core memory production.

Apollo AGC Core Memory: A Legacy

The Apollo AGC’s core memory stands as a testament to early technological advancements that propelled space exploration, setting the stage for modern memory systems that continue to evolve in complexity and capability.

Dive deeper into the technological advancements of the era with our in-depth article on the Apollo Guidance Computer (AGC), the computational genius behind the Apollo missions.