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A comment on Ask HN: Why do many CS graduates lack foundational knowledge?. Parent comment

Re:Ask HN: Why do many CS graduates lack foundational knowle... by thrown123098 on Monday March 20, 2023 @05:01AM (#35228949)
My computer is very much a Turing machine since each time it runs out of disk space I can buy more disks. The fact you think a Turing machine has infinite memory rather than finite but arbitrarily large memory tells me all I need to know about the sorry state of your theoretical education.
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by dgb23 on Monday March 20, 2023 @05:04AM (#35228966)
How much does an infinite amount of disk space cost?
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by oriolid on Monday March 20, 2023 @05:30AM (#35229152)
Nothing, if it's your users who buy it instead of you.
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by thrown123098 on Monday March 20, 2023 @05:07AM (#35228986)
Ignoramus educate thyself: https://en.wikipedia.org/wiki/Arbitrarily_large
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by rrobukef on Monday March 20, 2023 @08:34AM (#35230589)
A Turing machine is a mathematical concept. It has, by definition, infinite memory. A computer is just a real machine that can do similar things as a Linear Bounded Automaton, a Turing machine's little brother who'll never do quite the same things.
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by thrown123098 on Monday March 20, 2023 @09:31AM (#35231230)
Wrong: https://en.wikipedia.org/wiki/Arbitrarily_large
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by rrobukef on Monday March 20, 2023 @03:07PM (#35236941)
There is a physical limit to the number of disks you can add to your CPU. There is a physical limit to the memory you can address in your CPU (48-bits). It is not arbitrarily large.

Also wrong for Turing Machines, it really is infinite. That's a big difference to arbitrarily large. The halting problem is undecidable for TM's but not for arbitrarily large (you'll need precise definitions though).

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Re:Ask HN: Why do many CS graduates lack foundational knowle... by thrown123098 on Monday March 20, 2023 @06:44PM (#35239906)
It is left as an exercise to the reader to find a natural number which isn't arbitrarily large but calculable.
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by rrobukef on Tuesday March 21, 2023 @03:08AM (#35243289)
The tape size needed for a Turing machine is incalculable. Here's a reference to a proof: https://scottaaronson.blog/?p=2725.

The machine with 7918-states, Z, stops (well, Z cannot be proven to run infinitly long) iff. ZFC is consistent. For this it needs a finite amount of space but we cannot calculate how much. If we could calculate an upper bound we've proven ZFC is consistent.

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Re:Ask HN: Why do many CS graduates lack foundational knowle... by thrown123098 on Tuesday March 21, 2023 @08:23AM (#35245217)
Yes which is why the size if strictly finite but arbitrarily large.
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Re:Ask HN: Why do many CS graduates lack foundational knowle... by bigbillheck on Monday March 20, 2023 @09:49AM (#35231453)
> each time it runs out of disk space I can buy more disks.

There's only so many that you can buy.

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