14. OCR A Level (H046-H446) SLR4 - 1.2 Paging, segmentation and virtual memory
Summary
TLDRThis video explores memory management techniques, focusing on paging, segmentation, and virtual memory. It explains how programs are loaded into RAM and the challenges of memory allocation when space is fragmented. Paging divides memory into fixed-size blocks, while segmentation uses variable-sized blocks based on program structure. When RAM is full, virtual memory comes into play, offloading less-used data to the hard disk, creating an illusion of expanded memory and addressing the slowdown caused by limited physical memory.
Takeaways
- 💾 Memory Management: The video discusses memory management techniques, focusing on paging, segmentation, and virtual memory.
- 📈 RAM Usage: It explains how programs are loaded into main memory (RAM) and how memory is managed when programs are opened and closed.
- 🔄 Memory Fragmentation: The issue of memory fragmentation is introduced, where free space is not contiguous, preventing new programs from fitting.
- 🔄 Paging: Paging is a strategy where memory is divided into fixed-size blocks called pages, which are allocated to programs regardless of their size.
- 🔄 Segmentation: Segmentation is another strategy where memory is divided into variable-sized segments based on logical divisions of programs.
- 🔄 Efficiency: Paging can lead to inefficiency by splitting program instructions, while segmentation aims to keep related instructions together.
- 💾 Virtual Memory: When RAM is full, virtual memory is used to extend the available memory space by utilizing the hard disk for storage.
- 🔄 Swapping: The concept of swapping is introduced, where less frequently used parts of a program are moved to the hard disk to free up RAM for other programs.
- 📉 Performance Impact: The video explains that using virtual memory can slow down a computer because accessing data from the hard disk is slower than from RAM.
- 💡 Key Question: The video concludes by posing a key question about how computers handle running out of memory and the associated slowdown.
Q & A
What is the primary function of random access memory (RAM) in a computer?
-RAM serves as the main memory where the operating system and other applications are loaded for immediate access and execution by the CPU.
Why is it inefficient to move programs within memory to consolidate free space?
-Moving programs within memory is inefficient because it takes a significant amount of time and requires updating all addresses and references to free space, which can disrupt the program's operation.
What are the two main strategies for dividing up memory to solve the problem of non-contiguous free space?
-The two main strategies are paging and segmentation. Paging divides memory into fixed-size blocks, while segmentation divides memory into variable-sized sections based on logical divisions of the program.
How does paging differ from segmentation in terms of memory allocation?
-Paging allocates memory in fixed-size blocks regardless of the program's structure, which can lead to inefficient memory use. Segmentation, on the other hand, allocates memory in variable-sized segments that correspond to logical divisions of the program, leading to more efficient memory use.
What is the potential downside of paging when it comes to program execution?
-The downside of paging is that it can separate instructions within a program, such as those within a loop, into different parts of memory, which can lead to inefficiencies in program execution.
How does segmentation improve upon the limitations of paging?
-Segmentation improves upon paging by dividing memory into segments that correspond to complete sections of a program, allowing related instructions to be kept together and enhancing program execution efficiency.
What is virtual memory, and why is it used in modern computers?
-Virtual memory is a memory management technique that uses hard disk space to store data and instructions that are not immediately needed in RAM. It is used to give the appearance of having more memory than physically available, allowing more programs to be run simultaneously.
Why does a computer slow down when it runs out of RAM and starts using virtual memory?
-A computer slows down when using virtual memory because accessing data from the hard disk is significantly slower than accessing it from RAM. The constant swapping of data between RAM and the hard disk consumes additional time and system resources.
How does the operating system manage the transition of data between RAM and virtual memory?
-The operating system manages the transition of data between RAM and virtual memory through a process called swapping. When RAM is full, less frequently used data is moved to the hard disk, and when that data is needed again, other data may be swapped out to make room.
What is the role of the bootstrap program in loading the operating system into RAM?
-The bootstrap program is responsible for loading the operating system from the disk into RAM when the computer is turned on, initializing the system for further operations.
Outlines
💾 Memory Management Techniques
This paragraph introduces the concepts of memory management with a focus on paging, segmentation, and virtual memory. It uses a diagram to illustrate the process of loading programs into main memory and the challenges that arise when there isn't enough contiguous free space for a new program. The paragraph explains the inefficiency of moving programs within memory and introduces two strategies to overcome this: paging and segmentation. Paging divides memory into fixed-size blocks, while segmentation allows for variable-sized sections based on program structure. The paragraph also touches on the limitations of these methods and sets the stage for the discussion of virtual memory in the next paragraph.
🖥️ Virtual Memory and Its Role in Memory Management
The second paragraph delves into the concept of virtual memory as a solution to the problem of limited RAM. It explains how virtual memory allows the computer to use hard disk space to store instructions that are not immediately needed, thereby giving the illusion of having more memory than physically present. The paragraph describes the process of swapping out less frequently used instructions to the hard disk and swapping in other programs when needed, which helps in managing memory more efficiently. The video concludes by posing a key question about how computers handle running out of memory and the associated slowdown, inviting viewers to consider the practical implications of the discussed memory management techniques.
Mindmap
Keywords
💡Random Access Memory (RAM)
💡Paging
💡Segmentation
💡Virtual Memory
💡Main Memory
💡Operating System
💡Memory Management
💡Physical Memory
💡Logical Divisions
💡Contiguous Memory Allocation
💡Efficiency
Highlights
Introduction to memory management with a focus on paging, segmentation, and virtual memory.
Explanation of random access memory (RAM) and its role in loading the operating system and applications.
Challenge of fitting new programs into fragmented memory spaces.
The inefficiency of moving programs within memory and the need for a better solution.
Introduction to paging as a strategy for dividing memory into fixed-size sections.
Discussion on the limitations of paging due to its disregard for program structure.
Segmentation presented as an alternative with variable-sized memory divisions based on program logic.
Advantages of segmentation in managing memory more efficiently by keeping related program parts together.
Comparison of paging and segmentation in terms of memory division strategies.
The concept of virtual memory as a solution to running out of physical RAM.
Description of how virtual memory allows more programs to be managed than can fit in RAM.
Explanation of how virtual memory uses the hard disk to store less frequently used instructions.
The process of swapping programs between RAM and virtual memory to optimize memory usage.
The illusion of having more memory than physically available through virtual memory.
Key question posed: How does a computer handle running out of memory and why does it slow down?
Encouragement for viewers to pause and take notes on the similarities and differences between paging and segmentation.
Transcripts
in this video we discuss memory
management
with particular reference to paging
segmentation
and virtual memory
[Music]
so in order to understand this topic
we're going to use
a diagram on the left here so
effectively what we've got
is random access memory main memory
now when your computer first starts up
it loads the operating system
and then you interact with other
applications and programs
and they get loaded into memory so here
programs a b c and d have all been
loaded
program c has now been closed and the
memory has been released
program e arrives but as we can see it
won't fit
into either of the three spaces
available in main memory
now there is enough total free space
available it just doesn't have to be
located together
in a single block
now one solution could be to move the
location of program d
in memory so the free space is all
together
although this looks really simple to do
with our abstract diagram here
it's not actually very desirable to
operate like this in practice
it takes a lot of time to move a program
in memory or on disk
all the addresses and free space
references need updating
we actually need another solution now
there are two main strategies
both of which essentially evolve
dividing up memory
into smaller sections they are paging
and segmentation
so with pages the memory is divided into
fixed sizes all the same
pages are made to fit sections of memory
these pages are considered to be
physical divisions
and the programs are split up to fit
into these given number of pages
now paging takes no account of how
it splits the program only that it
splits it
into these fixed size pages it's quite
possible that it could separate the
instructions inside say a looping
condition
so they're in different parts of memory
and of course this is not very desirable
as it become quite inefficient
it would be better to keep those kind of
structures all together
well another option is segmentation
here the segments are different sizes
they're complete sections of program
so now we're dividing up memory based on
logical divisions
and not arbitrary physical divisions
so here program b has been closed
and the memory has been released
a new program e is loaded there's plenty
of free space so it just goes in
now program f arrives is too big to fit
in either of these three spaces but
based on logical and sensible divisions
segmentation can split the program into
two parts
and it places them in the available free
space as shown
leaving two smaller areas of free space
so as a summary here are the
similarities and differences
with paging versus segmentation you
might like to pause the video at this
point and take some notes before moving
on so after a while it's obviously
perfectly reasonable to have a situation
where main memory has become
full as is shown here now job
g ideally would like to run it would
seem we have to prevent the program from
loading at all
now this situation is far from ideal the
solution
is to make use of what we call virtual
memory
when programs and data are being fetched
and executed by the cpu
they are stored in ram however this
assumes that the memory is large enough
to hold all the programs being executed
in modern computers it's common to have
more than one program open at once
however you can store significantly more
programs on the hard disk compared to
ram
because byte for byte hard disk space is
much cheaper than ram
when you turn your computer on the
bootstrap program will load the
operating system from the disk into ram
when you use a computer every time you
double click an icon to load a program
it transfer those instructions into ram
but what happens when you run out of ram
as instructions are fetch one at a time
that means that some of the instructions
are not likely to be fetched in the near
future
therefore one solution is to transfer
instructions that are not being used
to a space on the hard disk and this is
known
as virtual memory
when these instructions are needed again
a different program can be swapped out
of ram to virtual memory
to make room for the instructions that
are now needed
this gives the impression that a
computer has more memory
than it actually has
having watched this video you should be
able to answer the following key
question
how does a computer handle running out
of memory and why does it slow down
[Music]
you
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