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Institute for Advanced Study Computer
The IAS Computer was one of the earliest stored-program computers, designed between 1945–1951 at the Institute for Advanced Study (IAS), Princeton University.
It was designed under the leadership of John von Neumann, who applied his theoretical model (now called the Von Neumann architecture) into a working machine.
The machine became a prototype — many later computers were modeled on its design, known as the IAS architecture.
Post–World War II (1940s–1950s), a time of rapid advances in electronics and computing.
Institute for Advanced Study (IAS), Princeton, New Jersey.
John von Neumann, a mathematician and physicist, famous for his work in quantum mechanics, game theory, and computer science.
Create a stored-program electronic computer → a machine that stores data and instructions in the same memory.
This idea was revolutionary compared to earlier computers like ENIAC, where programs were hardwired with switches and cables.
Von Neumann and his team conceptualized a machine based on the stored-program principle.
The idea: a flexible computer where software could be changed without rewiring.
Work began in 1948.
Main challenges:
By 1951, the IAS computer was working.
It was one of the first stored-program computers in the world.
The IAS Computer directly embodied the Von Neumann Architecture:
Arithmetic Unit (ALU): Performed addition, subtraction, multiplication, division, and logical operations.
Control Unit (CU): Fetched instructions from memory, decoded them, and executed them.
Size: 1,024 words, each 40 bits long.
A word could hold:
Memory stored both instructions and data → unified storage system.
Accumulator (AC): Stored arithmetic results.
Multiplier-Quotient (MQ): Helped with multiplication/division.
Instruction Register (IR): Held the current instruction.
Program Counter (PC): Tracked the next instruction's address.
Used punched card readers, printers, and other electromechanical devices.
The IAS computer's memory could store both instructions and data in the same memory space, implementing the stored-program concept.
Each 40-bit word could hold either one data value or two instructions, providing flexibility in how memory was used.
Each instruction was 20 bits.
A 40-bit memory word could hold two instructions.
Format of an instruction:
Opcode (8 bits): Specifies the operation (e.g., add, subtract, load).
Address (12 bits): Specifies the memory location of data.
Instruction = 00000101 000110101011
00000101 → Opcode for "ADD"
000110101011 → Address where operand is stored.
256 possible operations
4,096 memory locations
Instruction is fetched from memory into the Instruction Register (IR).
Control Unit decodes opcode → determines operation.
Data is fetched (if needed), ALU executes operation, result stored in AC or memory.
Program Counter moves to the next instruction.
💡 This fetch-decode-execute cycle is the foundation of how modern CPUs operate today.
Suppose we want to compute C = A + B.
Store values of A and B in memory.
LOAD A → puts A into AC.
ADD B → adds B to AC.
STORE C → writes result back to memory.
👉 This process in IAS was one of the first times programs controlled operations stored in memory instead of rewiring circuits.
Most early computers (EDVAC, IBM 701, MANIAC, etc.) were based on the IAS design.
Before IAS, computers like ENIAC required rewiring to change programs.
IAS allowed storing instructions in memory → flexible programming.
Allowed large-scale computations in physics, mathematics, and engineering.
Example: simulations of nuclear processes, advanced math calculations.
The IAS (Von Neumann) architecture is still used today in CPUs (with improvements).
Its design became the model for many early computers worldwide (often called "IAS-type machines").
Influenced machines like IBM 701, MANIAC, and others.
Very slow by modern standards (performed thousands, not billions, of operations per second).
Single memory for data and instructions caused the Von Neumann bottleneck (CPU and memory could not work simultaneously).
Required massive hardware (vacuum tubes) → unreliable and power-hungry.
Memory size (1,024 words) was very limited by modern standards.
🔍 Despite these limitations, the IAS Computer was revolutionary for its time and laid the groundwork for modern computing.
The IAS Computer (1951) was a pioneering achievement that shaped the future of computing.