Because that’s all that’s needed. 48 bits give you an address space of 256 terabyte. That’s a lot. You’re not going to see a system which needs more than that any time soon. So CPU manufacturers took a shortcut. They use an instruction set which allows a full 64-bit address space, but current CPUs just … Read more
The default page size is fixed by what the MMU (memory management unit) of the CPU supports. In 32-bit protected mode x86 supports two kinds of pages: normal ones, 4 KiB huge ones, 4 MiB Not all x86 processors support large pages. One needs to have a CPU with Page Size Extension (PSE) capabilities. This … Read more
Before I answer your questions (I hope I do), here are a few introductory remarks: Remarks The problem here is that “virtual memory” has two senses. “Virtual memory” as a technical term used by low-level programmers has (almost) nothing to do with “virtual memory” as explained to consumers. In the technical sense, “virtual memory” is … Read more
Yes every process has its own pagetables. They might be shared with the parent process(copy on write) or with other processes(shared memory). But in general every process has its own.
In singlelevel pagetable you need the whole table to access even a small amount of data(less memory references). i.e 2^20 pages each PTE occupying 4bytes as you assumed. Space required to access any data is 2^20 * 4bytes = 4MB Paging pages is multi-level paging.In multilevel paging it is more specific, you can with the … Read more
First, it’s platform dependent. In some architectures, stack is allocated from the bottom of the address space and grows upwards. Assuming an architecture like x86 that stack grown downwards from the top of address space, the idea is pretty simple: =============== Highest Address (e.g. 0xFFFF) | | | STACK | | | |————-| <- Stack … Read more
When people talk about sequential vs random writes to a file, they’re generally drawing a distinction between writing without intermediate seeks (“sequential”), vs. a pattern of seek-write-seek-write-seek-write, etc. (“random”). The distinction is very important in traditional disk-based systems, where each disk seek will take around 10ms. Sequentially writing data to that same disk takes about … Read more
The default sizes for initial heap and maximum heap are defined as a percentage of the machine’s physical memory, of which a production server nowadays tends to have a whole lot. You can choose both via the -Xms and -Xmx command line options.
Version of this answer with a nice TOC and more content. I will correct any error reported. If you want to make large modifications or add a missing aspect, make them on your own answers to get well deserved rep. Minor edits can be merged directly in. Sample code Minimal example: https://github.com/cirosantilli/x86-bare-metal-examples/blob/5c672f73884a487414b3e21bd9e579c67cd77621/paging.S Like everything else … Read more
Softwares run on the OS on a very simple premise – they require memory. The device OS provides it in the form of RAM. The amount of memory required may vary – some softwares need huge memory, some require paltry memory. Most (if not all) users run multiple applications on the OS simultaneously, and given … Read more