Program vs Process (low level concepts)
Summary
TLDRThe video script from 'Program is not a Process by Core Dumped' explores the nuances between a program and a process in computing. It explains that a program is a passive sequence of instructions stored on disk, while a process is an active, temporary instance of a program running in memory. The script delves into early computing history, the evolution of batch systems to time-sharing operating systems, and the concept of concurrency. It also discusses the memory layout of processes, including text, data, stack, and heap sections, and touches on the differences in how compiled and interpreted languages like C, Java, and Python are executed.
Takeaways
- 🖥️ Programs vs Processes: A program is a sequence of instructions stored on disk, while a process is an instance of a program running in memory, with its own allocated resources.
- 🧠 A process is active: Programs are passive entities stored on disk, but when they are executed, they become active entities known as processes.
- 💾 Memory allocation: Processes have distinct memory regions for instructions (text section), global variables (data section), and temporary data (stack and heap).
- 🔀 Single core concurrency: Early home computers popularized concurrency, where a single-core CPU switches between multiple processes to simulate multitasking.
- 📝 Compilation in C: In compiled languages like C, the program is converted into CPU instructions and saved to an executable file with data and instructions stored separately.
- 🐍 Interpreted languages: In Python and JavaScript, there is no compilation into machine code; instead, the interpreter executes the code at runtime, making them distinct from compiled languages like C.
- 📚 Interpreter process: In Python, when the interpreter runs, it loads the Python code into memory as data, while the interpreter itself becomes the active program (process).
- 📝 Text vs Data regions: The text section in memory remains constant for the duration of the process, while the data section may change based on runtime actions.
- 🔁 Recursive functions and memory: Stack memory, often limited, is used for function calls, and recursive functions can lead to stack overflows if too many layers are created.
- ⚙️ Separate processes, shared programs: The same program can run as multiple processes simultaneously, each having its own memory space but the same set of instructions (text section).
Q & A
What is the main difference between a program and a process?
-A program is a passive entity, typically an executable file stored on disk, while a process is an active entity that is created when the program is loaded into memory and executed. A process has its own memory space, including text, data, stack, and heap sections.
How does the memory layout of a process differ from that of a program?
-The memory layout of a process includes the text section (which holds executable code), the data section (holding global variables and constants), the stack (for function calls and local variables), and the heap (for dynamic memory allocation). A program is simply a file, while a process is a live execution with allocated memory.
What is the significance of the text section in a process?
-The text section contains the executable code of the program. It is a part of the process’s memory that remains constant in size and content throughout the execution of the process.
Why is recursion sometimes discouraged in programming, according to the transcript?
-Recursion can be discouraged because recursive functions use the stack for each function call, which can lead to stack overflow if the recursion depth is too high. Stack memory is limited, and exceeding it can crash the program.
What is the role of the heap in a process's memory layout?
-The heap is used for dynamic memory allocation during a process’s runtime. Memory from the heap is allocated and freed as needed, and the size of the heap can grow and shrink during the execution of the program.
How do interpreted languages like Python handle the difference between a program and a process?
-In interpreted languages like Python, the source code is not directly executed by the CPU. Instead, the Python interpreter (itself a program) is executed, and the source code is loaded into one of the interpreter’s memory sections (typically the heap) as data to be interpreted.
Why is it important to distinguish between a program and a process in computing?
-Distinguishing between a program and a process is important because a program is simply a file that can be executed, while a process is the running instance of the program with its own memory and resources. Multiple processes can run from the same program, but they operate independently.
How does Python handle global variables and string literals after compilation?
-After compilation in Python, global variables and string literals are stored in the data region of the process. They are separated from the CPU instructions and can be accessed during runtime without being part of the executable code itself.
What is concurrency, and how does it relate to early computer systems?
-Concurrency refers to the ability of a system to execute multiple processes or tasks at the same time, allowing for time-sharing. In early computer systems, this concept was introduced to allow multiple users or tasks to share the CPU's resources. Concurrency became popular with home computers, allowing single users to run multiple programs at once, even on single-core CPUs.
What happens when a Java program runs, according to the script?
-When a Java program runs, it is executed within the Java Virtual Machine (JVM). Java code is compiled into bytecode, which is then interpreted or just-in-time compiled by the JVM. Each Java process typically runs with its own instance of the JVM.
Outlines
🖥️ Introduction to Programs and Processes
The narrator expresses their interest in a YouTube channel that delves into technical computer science concepts. The discussion opens with a question about the difference between a program and a process. The narrator offers an initial explanation, stating that a program is stored on disk and is static, while a process is in memory and more temporary. Early computer systems ran jobs in batch mode, but with the rise of time-sharing, user programs were executed concurrently, allowing multiple processes to run simultaneously. This leads to a deeper examination of the distinction between programs and processes.
💡 Concurrency and Memory Allocation
The video explores how early home computers popularized concurrency, even with single-core CPUs. The narrator speculates that concurrency refers to multiple processes running at the same time with the CPU context-switching between them. They dive into the difference between programs and processes, pointing out that a program is a set of instructions, while a process is an active instance of those instructions. The narrator begins contemplating how the memory sections of programs, such as global variables and stack memory, function once a program is compiled into executable code.
📂 Memory Layout and Processes
The narrator dives deeper into how programs interact with memory when they become processes. They explain that when a program is loaded into memory, it is divided into sections like the 'text section' for code and 'data section' for variables. While the text section remains unchanged, the data section can vary based on the program’s runtime behavior. The concept of memory allocation is discussed in terms of recursive functions and variable memory needs, explaining how a process uses memory differently than a static program.
🔍 Understanding Processes with Examples
The video provides a practical example of processes using a text editor. Opening two files in separate windows results in two different processes, even though the program is the same. The narrator highlights that each process has its own memory space, though the code (text section) is the same. They further explain that processes are an operating system-level concept, each with its own ID and memory management. While the video doesn’t go too deep into technical details, it emphasizes that a process is more than just an active program—it’s a complex entity managed by the OS.
💾 Interpreted Languages and Processes
The narrator discusses how interpreted languages like Python and JavaScript differ from compiled languages like C. Unlike compiled languages, which turn source code into executable files, interpreted languages run through an interpreter. Each time a Python program runs, a process is created, and the interpreter reads the source code. The narrator brings up an interesting point about how even though Python has a compilation step to bytecode, it's often overlooked due to its runtime nature. The interpreter manages both the text and data sections for these interpreted programs.
Mindmap
Keywords
💡Program
💡Process
💡Memory layout
💡Text section
💡Data section
💡Heap
💡Stack
💡Concurrency
💡Interpreter
💡Compilation
Highlights
The distinction between a program and a process: a program is a passive entity stored on disk, while a process is an active entity in memory.
Concurrency in early computers allowed a single user to run multiple programs simultaneously, even with a single-core CPU, using context switching.
In computer science, programs are referred to as processes when executed, not programs.
The text section of memory stores executable code, while global variables and constant values are stored in the data section.
Heap and stack memory regions complement the data section for runtime memory allocation, such as user inputs and temporary variables.
The stack is used for local variables and function calls, while the heap is for dynamically allocated memory.
The stack has limited memory, which is why stack overflows can occur, especially in recursive functions.
The text section of a process's memory never changes in size or content during execution, but the data section's contents may vary.
In interpreted languages like Python, the interpreter itself is a process, while the Python source code is treated as data for the interpreter.
Global variables and string literals in a compiled C program are saved in the data region, while local variables go to the stack.
The difference between compiled and interpreted languages: in Python, source code is not executable by itself but is processed by the interpreter.
Processes associated with the same program, such as opening two text files in the same editor, operate in separate memory spaces.
Java programs are run by the Java Virtual Machine (JVM), which operates as a separate process to execute Java bytecode.
Even though Python source files are text, they are compiled to bytecode before execution by the interpreter for performance optimization.
Recursion, while theoretically valid, is discouraged because of memory limitations in the stack, which can lead to stack overflow.
Transcripts
program is not a process by core dumped
probably my new favorite YouTube channel
because it takes me back to the days
when I was just getting a computer
science degree and I was actually
learning about things that were
interesting most people learn to code so
they can actually build things that are
genuinely useful not me I just like
understanding how things work and this
channel is going to let us do that a
question that arises in computer science
is what to call all the activities
performed by the CPU I hate to pause it
right now but I think so just based on
the title The first thing that I think
of is that a program versus a process
what's the difference um I guess a
process is just an instance of a program
for example like for one program you can
have multiple processes and a program I
believe is just going to be stored on
your dis so it's like persisted there
versus a process is going to be stored
in memory and it's going to be
shortlived or temporary at the very
least early computers were batch systems
that executed work units called jobs
as I discussed in my video about
concurrency when time sharing operating
systems emerged they were designed to
share the CPU among multiple users so it
was said that those systems ran user
programs interesting I actually don't
know very much at all about very early
computers eventually the home computer
Market popularized the use of
concurrency to allow a single user to
run multiple programs at once that's
very interesting actually let me replay
that did he say concurrency eventually
the home computer Market popularized the
use of concurrency the use of concurr
currency what he means by that I think
is not like this is like the invention
of a multi-threaded or like multi-core
CPU it's more that just you have
multiple processes running at the same
time and then the CPU is going to
contact switch between them uh that's
very interesting so that was probably
even with a single core CPU to allow a
single user to run multiple programs at
once but in computer science we don't
refer to these entities as programs but
rather as
processes so today we are going to learn
the difference that's very interesting
to this shows me how much I actually
don't know because I thought Linux is
just I I believe from its birth was
using like processes so that's
interesting it's kind of hard to believe
that there was a point you literally
couldn't run multiple processes at the
same time just imagine living like that
today I don't even think it's possible
Concepts hi friends my name is George
and this is core dumped for the vast
majority the answer to this question
seems obvious programs after all that's
what CPU does right it runs programs but
as I mentioned before in computer
science the correct term is process
that's technically correct I wonder how
mad people would get though if you just
said program kind of reminds me of the
other day how I said pointer in
technically the wrong context informally
a process is usually defined as a
program in execution even though this
definition is technically correct what I
find frustrating is that it is not
enough to help a casual reader
understand what a process is
so let's start by establishing what a
process is not think about this
interesting I think he's right CU like
the devil is in the detail to say that a
process is an instance of a program
isn't really getting into the hardware
and like like I said kind of at the
beginning the hardware matters like the
dis versus like the memory where each is
stored and how it's run and all that
different programs are obviously
intended for different purposes but in
many respects they are similar when
executing as they all reduce to the
fundamental actions performed by the CPU
and here's where we can start making
distinctions a program is a sequence of
instructions and the data that the CPU
needs to accomplish a specific
task now if you carefully Analyze This
description you'll notice that it can
also describe an executable file and
that's because that's pretty much what a
program is let's say like you have a c
program you compile it it turns into
like CPU instructions that the CPU is
going to load into memory and execute
that makes sense so what is this data at
the top of my head I actually don't know
cuz the executable file it has data
itself what does that mean cuz I know
when a process is running it's going to
have some memory allocated like the
stack space Etc but the executable file
itself has data I'm curious about that
so I wanted to at least have like a
little bit of understanding of what that
meant so I just went to chat gbt and
asked it so can you give me a simple
example of a c program after compilation
what parts of it would be the CPU
instructions and which parts of it would
be the data I think that the CPU
instructions are like Rel relatively
straightforward in terms of like if you
had conditional statements loops and
things like that like the control flow
that makes sense that those would turn
into CPU instructions but I was
surprised to see that so if you have
like Global variables and for example
string literals those are actually saved
in the data region after the program is
compiled and so local variables like
this are going to be as we would kind of
expect pushed onto like the stack space
and I would assume like the same thing
with recursive calls of course but it's
interesting to me that a string literal
like this would be saved not as like a
CPU instruction but rather in the data
region so what does that mean like if I
had multiple print statements would that
same string be copied multiple times I'm
assuming not CU that sort of
optimization could be made but actually
now that I think of it on second thought
if there are distinct strings and you
want to update one of the strings you
don't necessarily want both strings to
be updated I think if we were to dig
deeper into this we would probably be
getting really into the realm of like
operating system so I guess I won't do
that right now but it does make sense
that a lot of variables and just large
amounts of data are going to be stored
in the data region of an executable file
separate from the code instructions and
so all of that is going to be loaded
into memory when it's actually run but
there's going to be separate memory
regions like the stack and probably the
Heap that can complement the data
section a program is that passive entity
that resides in your storage waiting for
you to click on it to tell the the
computer to start running
it as I've mentioned many times in the
past to run a program it first needs to
be loaded into memory as that's where
the CPU can start fetching instructions
and
data when loaded into memory the section
containing the executable code is known
as the text section while data such as
Global variables and constant values is
loaded into the data section okay I mean
he literally just answered the question
sorry about that but running a program
requires more than these two sections it
also need extra space in memory to store
all the data generated at runtime like
user input and temporary results or
variables yeah so he said at runtime
like there's going to be separate memory
so I don't think he's probably going to
have enough time to like go into the
details of every little thing in this
video but I'll try to add like my
commentary which is that so conceptually
think about it for a second why would we
not have the memory up front for
something like a recursive function or
even different variables that may or may
not necessarily be allocated why do we
need like a variable amount of memory
because you don't necessarily know you
could have a recursive function
depending on the input to the program it
might stack up 10 times before hitting
the base case or depending on a second
input it might stack up 20 times if you
pre-allocate the memory you don't
necessarily know how much memory it's
going to take now even the stack is
technically Limited in memory that's why
like stack Overflow occurs like this
region called the stack which recursive
functions use it will hit a limit like
there is a limit to this I think you can
sometimes update that limit many
languages will have like a default limit
size but anyways we already know a lot
about the stack and the Heap such as the
fact that they are growing and shrinking
in size all the
time the tech section is the only one
that never change neither in size nor
content interesting that would make
sense based on like the CPU instructions
text is not going to change stack is
obviously growing for reasons I talked
about not just for recursive functions
but also like one function calls another
it's going to go on the stack when that
function finished it's going to return
back to the previous function the Heap I
actually don't remember off the top of
my head but I'm pretty sure one program
if it's using Heap memory the amount of
memory that that program is actually
using from the Heap could change but
theoretically you should be able to use
as much memory as your computer has uh
for the Heap let me actually just double
check that just from our cursory Google
search I guess this part is actually AI
generated but it does look like a
program can use unlimited amounts of
Heap memory what's the default stack
memory limit in C for example um it
looks like it's 1 Megabyte I don't know
if that depends on the compiler but
again like you can see that this is like
relatively small so it's reasonable that
you could hit a stack Overflow even if
there's not infinite recursion like
that's why recursion is actually not
good and you're hearing this from me the
data structures guy on YouTube that
generally speaking you don't want to do
recursion even for valid recursion you
could hit the memory limit anyways but
we can't say the same about the data
section because even though it doesn't
change in size its content may varies
depending on what the running program is
doing as you can see so the data region
can vary in size I mean if this is part
of the executable I wonder if that means
that at runtime that that is like the
amount of memory that's being used by
that data region is going to change but
like all that memory should be allocated
for the programmer maybe I'm
misunderstanding let me just replay it
just in case can't say the same about
the data section because even though it
doesn't change in size its content may
varies depending on what the running
program is
doing as you can see even though
initially we loaded the program into
memory when running this layout can no
longer be considered as a program of
course not it has now become a
process and please note that this is the
memory layout of the process not the
process
itself the reason this definition is
often con that's interesting so that's
the memory layout of the process but not
the process itself so how do you define
a process in my head it's an operating
system level unit right like the
operating system is managing the process
it gives it an ID if there are multiple
threads that are a part of that process
they will possibly share memory I guess
we're getting overly technical let's
just continue considered informal is
that the notion of what a process is is
far too complex to be captured in just a
few words we're not going to go into
technical details in this video because
there's a video about processes already
scheduled but for now let me help you
get an idea of what a process
is consider that little program that
comes with your operating system to open
text
files now imagine we have two files to
read if we open both files the operating
system will launch the text editor app
twice this results in two separate
Windows each displaying a different text
file both are the same program but two
completely different processes
right each process has its own memory
space of course while the content of the
text section in both processes memory is
identical since they are the same
program the data they are working with
is different right so that obviously
makes sense and it also makes sense that
in a text editor all of the data would
be going to the Heap you again wouldn't
want to run out of like stack space for
that imagine just declaring a massive
variable with megabytes like a megabyte
long string or something like that
probably want to avoid something like
that in this example the first process
is working with a much larger text file
than the second so it naturally requires
more memory to manage its
data and if you're a casual viewer
hopefully that's everything you needed
to understand the difference between a
program and a
process I are we casual viewers I don't
feel like I'm a casual viewer I always
want to know like the exact details and
by the way definitely subscribe to this
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dumped I don't want to just call him
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I emphasize that a program by itself is
not a process a program is a passive
entity whereas in contrast a process is
an active entity although two processes
may be associated with the same program
they are nevertheless considered two
separate execution
sequences I know that having a notion of
what a process is is not the same as
being able to Define it in technical
terms but as I mentioned earlier a
dedicated video on processes is coming
soon this episode is not over though
everything I've discussed so far makes
sense for compil languages when using
languages like C or rust the result of
the compilation is an executable file
that is the program itself but what
about interpreted languages like python
or JavaScript where there is no
compilation
process in Python for example every time
we want to run code we must first
instruct the computer to run The
Interpreter and then one thing I
actually want to go back to is he put
Java in the same realm as interpreted
and so that to me actually does make
sense given that like when you're
running a piece of java code is it the
code that's being executed because for
people who don't know Java turns into
like bik code and then there's a
separate program called the Java virtual
machine which then runs that Java code
so in a sense I think it is interpreted
it really is because what's running is
the Java virtual machine at least an
instance of it I'm actually not an
expert on Java if somebody wants to
comment maybe we can answer this
ourselves let's use Claude this time and
so I asked when a get away when a Java
process is running does it get its own
instance of the Java virtual machine yes
when a Java process is running it
typically does so this may or may not be
correct I'm going to assume it is
because for something basic as this I
would think Claude is correct we could
also Google this but so that's very
interesting so in that sense yeah I mean
Java definitely does feel like a
interpreted language I don't want to
start a debate or anything and in the
same realm I actually recently learned
this that python is also compiled like
there is a compil step like I used to
think like I had a very naive
understanding of how the python
interpreter worked I thought it
literally just read the python text
files line by line but there is a
compilation step so what is the
compilation step with python code and
how does it differ from java compilation
okay so there is a compilation step in
Python it's compiled into bite code but
it happens at runtime I believe there's
not an actual separate compilation step
so that honestly makes me feel like you
could not know that you could not know
that there's a compilation step in Java
just like you could ignore like the just
in time compilation with JavaScript and
you'd probably be fine I'm assuming this
is mainly done for optimization reasons
was there a point where python did not
have a compilation step why does it
exist or performance so it sounds like
it always was there and mainly does EX
for performance reasons or JavaScript
where there is no compilation
process in Python for example every time
we want to run code we must first
instruct the computer to run The
Interpreter and then tell The
Interpreter to execute our
code right so every time we run a python
file or Python program we're creating a
process and that process encapsulates
the python interpreter and it's going to
specifically be using the file itself
self as like the executable as the
instruction set not the instruction set
as the
instructions in other words there are
now two passive entities involved the
python interpreter which is a program
okay right so there's a separate unit
running for that process not just the
CPU reading like the lowle instructions
there are higher level instructions
involved file which is practically a
text file I would like to highlight here
the fact that the python source file is
not a program remember that source code
is just text that computers cannot
understand and therefore cannot execute
I guess in this case and maybe I'm
getting overly technical but even let's
say you took that python file and it
turns into bite code the distinction
between This and like that c program
example we were looking at towards the
beginning is I wonder if this python
when it's compiled into the bite code in
the bite code I wonder if there's a
separate region for the data versus like
the instructions I mean I wonder if that
matters at all but that's just something
that came to my mind so in this kind of
situations the program we're actually
asking the computer to run is The
Interpreter not the python code we
wrote once this new process is created
it has its own memory region with text
and data sections right I mean of course
every process has a text and data
section but I wonder how that relates to
like the bik code or like how like the
Java virtual machine does it this is
from the operating systems perspective
but from the python interpretor
perspective it's going to be reading
like the bik code where's the bik code
probably within the text
I think I'm just confusing myself maybe
they are distinct as well as a stack and
a heap just like any other
process the key Point here is that
what's loaded into the text section is
not our python source code but the
executable code of The Interpreter our
source code is loaded by The Interpreter
process into one of its data sections
most likely the Heap because it serves
as the data The Interpreter will work
right that's very interesting so this is
the program that's running for it to
know how to execute it's going to keep
fetching the data from the Heap that's
very interesting because still when a
program is running it's not just running
from top to bottom like there's control
flow for example like you might have
some instructions but if the if
statement does not evaluate to true that
if statement is going to be skipped that
must mean when you have a python
interpreter it's going to go through the
memory it's sure it can read through the
memory but like that itself needs to be
coded to skip certain parts of the code
so it's almost like when you're creating
an interpreter in a sense you're kind of
creating like an abstraction for like a
CPU work with to read and
interpret and let's wrap it up for now
compilers and interpreters deserve their
own videos since I'm committed to
continue releasing quality content once
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encourage you guys to subscribe as well
honestly his channel is fantastic
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