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The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialing of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

With that structure the ENIAC did rather reassemble a contemporary accounting machine like the IBM 402 than anything we think of a computer today. Including programming by wiring function blocks like the 402 did by using a plugboard. The main difference was being tube based instead of electro-mechanical (*4).

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

*4 - Ken Shirriff has provided a very nice and detailed description about how a 402 was plugboard programmed to perform iterations over input data. The terms used ((sub)total, etc.) are applications specific and may need some thinking to reveal the modern equivalence behind.

The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialing of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

With that structure the ENIAC did rather resemble a contemporary accounting machine like the IBM 402 than anything we think of a computer today. Including programming by wiring function blocks like the 402 did by using a plugboard. The main difference was being tube based instead of electro-mechanical (*4).

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

*4 - Ken Shirriff has provided a very nice and detailed description about how a 402 was plugboard programmed to perform iterations over input data. The terms used ((sub)total, etc.) are applications specific and may need some thinking to reveal the modern equivalence behind.

The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialling of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

With that structure the ENIAC did rather reassemble a contemporary accounting machine like the IBM 402 than anything we think of a computer today. Including programming by wiring function blocks like the 402 did by using a plugboard. The main difference was being tube based instead of electro-mechanical (*4).

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

*4 - Ken Shirriff has provided a very nice and detailed description about how a 402 such was programmed to perform iterations over input data. The terms used ((sub)total, etc.) are applications specific and may need some thinking to reveal the modern equivalence behind.

The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialing of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

With that structure the ENIAC did rather reassemble a contemporary accounting machine like the IBM 402 than anything we think of a computer today. Including programming by wiring function blocks like the 402 did by using a plugboard. The main difference was being tube based instead of electro-mechanical (*4).

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

*4 - Ken Shirriff has provided a very nice and detailed description about how a 402 was plugboard programmed to perform iterations over input data. The terms used ((sub)total, etc.) are applications specific and may need some thinking to reveal the modern equivalence behind.

The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialling of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

The ENIAC was the first programmable, electronic, general-purpose digital computer.

A debatable claim, as each of those attributes (*1) is flawed in one way or another.

When we say "programming by rewiring", what does that actually mean?

ENIAC was just a bunch of components (mostly accumulators *2) which needed to be connected by plugging of wires to create a data path as well as control logic and dialling of knobs to select certain functions to be performed. Each of the 20 accumulators had 12 knobs to be set to the right combination to determinate what it will do with incoming pulses in relation to its content and when and what it will pulse out (*3).

After that the parts became a special one-function computer.

Well, that is if everything worked out - which it mostly didn't. Not so much because of logical errors as due to timing issues. Accumulators receiving their input too late, or control pulses being not recognised and so on.

With that structure the ENIAC did rather reassemble a contemporary accounting machine like the IBM 402 than anything we think of a computer today. Including programming by wiring function blocks like the 402 did by using a plugboard. The main difference was being tube based instead of electro-mechanical (*4).

Is it similar to programming an FPGA?

Kinda, but not really. Programming an FPGA is done by storing information in memory cells which in turn control connections between elements (gates etc.) and buses. ENIAC in turn was physically rewired each time to solve a new task.

In addition, each of the elements had controls to set what subfunction was to be done.

In that form it became a 'new' one-function machine.

The closest equivalent would be a number of TTL ICs on a breadboard which can be (re)wired to create a desired circuitry. Or maybe those nice 1970s trainers like Heathkit's ET-3xxx series, or Tandy's Science Fair sets. In fact, for all building blocks of the ENIAC (Clock, Sequencing, Accumulators, Multiplexers, etc.) similar units existed as TTL or combination thereof.

It wasn't until later that those connections were put into a formalized scheme which in turn could be 'programmed' by flipping switches instead of plugging wires. Again later when those switches were replaced by a loadable control store - at that point the comparison with an FPGA becomes more likely.

What is the "magic" of ENIAC that makes it "programmable"?

The magic was not being a single function device but being reconfigurable by rewiring. All in the basic sense of 'programmable' is that there's a procedure that can be changed.

*1 - If at all, and using all those adjectives with their modern meaning, then the Manchester Baby is, IMHO, the first machine that fits. Maybe less capable than ENIAC, but by no doubt regarding those requirements.

*2 - Today one would call them rather ALU with a register included plus logic attached to control transfers of input or results (values or signals).

*3 - ENIAC was for most parts a serial design.

*4 - Ken Shirriff has provided a very nice and detailed description about how a 402 such was programmed to perform iterations over input data. The terms used ((sub)total, etc.) are applications specific and may need some thinking to reveal the modern equivalence behind.