I'm wondering if I can use grub to switch to long mode then load a 64-bit kernel? I want grub to switch to long mode, setup page tables so the map one-to-one virtual to physical addresses and setup enough page tables to cover physical memory.
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is it possible to replace a ram with higher storage on a machine with a processor of low speed? is speed of processing increased or decreased.
i want to replace the ram drive of my machine with a higher storage ram so that I can try to manipulate the processor speed without changing the processors, will it work?
Yes. You can use faster RAM, currently up to DDR4-4800MHz. Using higher capacity RAM would also be useful if running out of RAM capacity is what’s slowing you down. Using a high-speed solid-state drive (SSD) would also speed up task that require reading or writing from storage, including booting up the computer and running programs that use a lot of assets on the computer. You can also overclock both your CPU and RAM to make them faster, but this may void your warranty.
Additionally, you can use software. For example, you can use CCleaner to remove useless files which clutter your computer. You can also use it to disable unneeded scheduled tasks that your computer runs. If your computer has a spinning-disc hard drive, then you can try defragmenting it by using the built-in Windows defragger, or you can use the Defraggler program from the same people who make CCleaner. Of course, you can also try deleting programs or files you no longer need or use if it’s limited hard drive capacity that’s slowing you down.
If it’s web browsing that’s slow, you may want to consider using a faster browser, like Google Chrome or Firefox. You can also install browser extensions/add-ons like AdBlock and Ghostery to prevent unneeded things from being loaded on pages, making pages load faster.
I am reading about logical and physical addressing. I am confused that when a binary file is run, does it pass first through the CPU where the logical address are generated or is it directly copied to the physical memory ?
when a binary file is run, does it pass first through the CPU where the logical address are generated or is it directly copied to the physical memory ?
Typically some code somewhere loads the executable file's headers into memory, and then uses information from the headers to figure out where various pieces of the file (sections - e.g. .text, .data, etc) should be in virtual memory and what each virtual page's virtual permissions should be (if writes are allowed, if execution is allowed).
After this, areas of the virtual address space are set up. Often this is done by memory mapping the relevant part of the file into the virtual address space, without actually loading them into physical memory. In this case each page's actual permissions don't reflect the page's virtual permissions (e.g. a "read/write" page might be "not present" initially, and when software tries to read from the page you'll get a page fault and the page fault handler might fetch the page from disk and change the page to "present, read only"; and then later when software tries to write to the page you might get a second page fault and the page fault handler might do a "copy on write" so that anything else using the same physical page isn't effected and then make the new copy "read/write" so that it matches the original virtual permissions).
While this is happening; the OS could (depending on amount of free physical RAM and whether storage devices have more important data to transfer) be prefetching the file data from disk (e.g. into VFS cache), and could be "opportunistically" updating the process' page tables to avoid the overhead of page faults for pages that have been prefetched.
However; if the OS knows that the file was on unreliable and/or removable media it may decide that using memory mapped files is a bad idea and may actually load the needed executable's sections into memory before executing it; and an OS could have other features that cause the file to be loaded into RAM before it's executed (e.g. if the OS checks that an executable file's digital signature is correct before allowing the file to be executed, then the entire file probably needs to be loaded into memory to allow the digital signature can be checked, and in that case the entire file is likely to still be in memory when virtual address space is set up).
You need to read an entire book on these topics and spend several weeks on that
But Operating Systems: Three Easy Pieces is a good book, and it is freely downloadable.
Once you have read it, look perhaps also into osdev.org for practical things. And don't forget free software OSes such as Linux, e.g.
https://kernelnewbies.org/
Be aware of copy-on-write and virtual address space...
An executable files is generally an interpreted program itself that is executed by the loader. The executable contains instructions that tell the loader how the program should exist in VIRTUAL memory. By that, I mean the instructions in the executable define how the initial VIRTUAL representation of process address space.
So when the executable starts, there is only a virtual representation of the address space in secondary storage. As the program executes, it starts page faulting repeatedly to load pages into memory. After the initial load, the page fault rate dies down.
The executable NORMALLY only contains logical addresses.
I can see from my OS the informations about my hard disk, RAM and CPU. But I've never told my OS these info.
How does my OS know it?
Is there some place in the hard disk or CPU or RAM that stores this kind of information?
Is there some standard about the format of this kind of information?
SMBIOS (formerly known as DMI) contains much of this information. SMBIOS is a a data structure/API that is part of the BIOS/UEFI firmware and contains info like brand and model of the computer, etc.
The rest is gathered by the OS querying hardware directly.
Answer grabbed from superuser by Mokubai.
You don't need to tell it because each device already knows (or has a way) to identify itself.
If you get the idea that every device is accessed via address and data lines, and in some cases only data lines then you come to the relaisation that in those data lines you need some kind of "protocol" that determines just how you talk to those devices.
In amongst that protocol you have commands that say "read this" and "send that" or "put this over there". It is also relatively easy to have a command that says "identify yourself" which, rather than reading a block of disk or memory or painting a pixel a particular colour, will return a premade string or set of strings that tell the driver or operating system what that device is. Using a series of identity commands you could discover a device type, it's capabilities and what driver might be able to work with it.
You don't need to tell a device what it is, because it already knows. And you don't need to tell the operating system what it is because it can ask the device itself.
You don't tell people what they're called and how they talk, you ask them.
Each device has it's own protocol for these messages, and they don't store the details of other devices because to do so would be insane and near useless given that you can remove any device at any time. Your hard drive doesn't need to store information about your memory or graphics card except for the driver that the operating system uses to talk to it with.
The PC UEFI specification would define a core set of system specifications that every computer has, allowing the processor to be powered up and for a program stored in an EEPROM to begin the asbolute basic system probing necessary to determine the processor, set up the RAM, find a disk and display and thus continue to boot the computer.
From there the UEFI system would hand over to the operating system which would have more detailed probing and identification procedures, but it all starts at the most basic "I have a processor, what is around me?" situation.
ARM's aarch64 has an AT (Address Translate) instruction that runs a virtual address through a stage of address translation returning a physical address in PAR_EL1, along with status to indicate whether the translation exists. See ARMv8 ARM, Section C5.5.
The question is: does x86_64 have the equivalent? Intel's System Programming Guide (Volume 3, Chapter 5) talks about pointer validation, but these methods seem to apply to segment-level protection, and there do not appear to be any page-level protection pointer validation instructions.
Is anybody aware of an ARMv8-AT-like instruction for x86_64?
No, the x86-64 instruction set does not have an instruction to perform physical-to-virtual address translation. It only has basic instructions like setting the page directory register, invalidating addresses, and enabling paging.
If you want this functionality on x86-64, I'm afraid you need to be in supervisor mode to do so. You would read the CR3 register, possibly change a few page table mappings to access the physical addresses you need, and perform the address translation by manually walking the page directory and tables.
Your question raises a question in response: For what purpose do you need to know about virtual-to-physical address translations? Paging is supposed to be transparent to application programs, and it is rare to have a good reason to know the physical memory address corresponding to a particular virtual memory address.
I am currently learning about Virtual Memory within the OS. I recently learned that access rights are stored in the page tables and so I am wondering if you can modify your own page tables? Does the hardware enforce protection from this?
Yes, you can modify your page tables—to some degree. Most operating system have system services to allow you to map and unmap pages to your address space (thus modifying your page tables).
Because page tables are stored in the system address space invariably with access limited to kernel mode, you have to modify the page tables in kernel mode. That means doing it through a system service that executes in kernel mode.
Of course you are limited to the types of modification you can make by the system services.
No, you (as user code) cannot directly modify the page tables for your processs, or any other process.
The page tables are manages exclusively by the kernel. They are stored in physical memory which is not mapped into userspace.
The hardware (specifically the MMU) enforces this protection just as it protects all of the kernel data and code.