x64 Virtual Address Translation

🔥 Learn How x64 Virtual Address Translation is Performed
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Video Creator: rexir
📜 Video Description:
Virtual memory serves as a key component in the architecture of contemporary operating systems, not excluding Windows. Essentially, it's an ingenious abstraction layer that empowers processes by creating an illusion of a vast, continuous memory block, despite the fact that the actual physical memory is often considerably smaller and shared among numerous processes.
At its core, virtual memory hinges on the idea of address translation, shifting from a "virtual" framework, leveraged by programs and processes, to "physical" addresses that point to concrete locations in the hardware's memory.
Virtual memory address translation
Private Virtual Space for Processes: Windows grants each process its own exclusive virtual address space. In the realm of 32-bit Windows, this typically amounts to 4GB of space (2^32 bytes). However, for 64-bit variants, the virtual address space is exponentially larger (theoretically 2^64 bytes, but practically curtailed by hardware constraints and Windows' architectural design).
Mapping Virtual Memory to Physical Memory: There isn't a direct correlation between virtual and physical memory. The operating system curates a map, dubbed a page table, that links every virtual memory address to a coinciding physical memory address.
Understanding Page Tables: A page table, housed in memory, holds an entry for every memory page a process employs. Here, a page represents a fixed memory block, usually 4KB on most systems. Each entry specifies the physical memory address where the page resides.
The Role of the Memory Management Unit (MMU): Residing within the CPU, the Memory Management Unit (MMU) shoulders the responsibility of translation. When a process seeks to access a memory location, it supplies a virtual address. The MMU, employing the page table, transposes this into a physical address. Dealing with Page Faults: In the event of a process requesting an address absent from the current page table (for instance, if the corresponding page is on the hard disk due to infrequent use), a page fault is triggered. Following this, the OS promptly loads the requisite page into physical memory and updates the page table.
Multilevel Page Tables and the TLB: Current systems employ multilevel page tables to minimize memory usage, along with a Translation Lookaside Buffer (TLB) to cache recent translations and hasten the process. Moreover, modern Windows versions harness a feature known as Physical Address Extension (PAE) to access beyond 4GB of memory.
The OS and the MMU collaborate to ensure that the virtual memory address translation process is entirely transparent to the process or program. Virtual Address Translation
Diving deep into Windows Virtual Memory, we uncover a cleverly designed system of mapping processes into their own isolated memory spaces, thereby ensuring seamless operation even in the face of limited physical memory resources. Windows Page Tables, a cornerstone of the operating system, play a pivotal role in maintaining a mapping between virtual memory addresses and their corresponding physical memory counterparts.
Shedding light on x64 Address Translation, it's a fascinating interplay of hardware and software where the Memory Management Unit (MMU) utilizes a set of page tables to translate virtual addresses into physical memory addresses. The Windows Memory Management Unit (MMU), while a largely overlooked component, is truly an unsung hero, responsible for the critical task of transforming virtual memory addresses into physical ones.
Page table translation, a mechanism in the heart of memory management, helps map virtual addresses to physical, enabling processes to operate in their own memory space. When we probe into the complexities of 64-Bit Virtual Memory Address Translation, we see that it allows Windows to manage a big address space, far beyond the confines of physical memory.
Virtual Address Translation
With 64 addressable bits on an x64 system, it's staggering to contemplate the vast 18.4 exabytes of virtual memory space available to a Windows process, an enormity that stands testament to the power of computing. A single Windows Page Table Entry, though small in size, holds information about the memory it represents.
0:00 Memory Address Translation
0:40 Types of Page Tables
1:15 The 64-Bit Address Distribution
1:54 Page Table Entry
2:25 Decoding of Bits
3:10 Write Through & Cache Disabled
3:59 Accessed & Dirty Bits
4:17 Large & Global Bits
4:45 CopyOnWrite & Prototype Bits
5:32 Write Bit
6:29 No Execute Bit