About infos about how to enable pagination

Author: SamyPesse

Chapter-8/README.md

@@ -21,9 +21,9 @@ In a paged system, each process may execute in its own 4gb area of memory, witho
 The translation of a linear address to a physical address is done in multiple steps:
 
 1. The processor use the registry `CR3` to know the physical address of the pages directory.
-2. The first 10 bytes of the linear address represent an offset (between 0 and 1023), pointing to an entry in the pages directory. This entry contains the physical address of a pages table.
-3. the next 10 bytes of the linear address represent an offset, pointing to an entry in the pages table. This entry is pointing to a 4ko page.
-4. The last 12 bytes of the linear address represent an offset (between 0 and 4095), which indicates the position in the 4ko page.
+2. The first 10 bits of the linear address represent an offset (between 0 and 1023), pointing to an entry in the pages directory. This entry contains the physical address of a pages table.
+3. the next 10 bits of the linear address represent an offset, pointing to an entry in the pages table. This entry is pointing to a 4ko page.
+4. The last 12 bits of the linear address represent an offset (between 0 and 4095), which indicates the position in the 4ko page.
 
 ![Address translation](./paging_memory.png)
 
@@ -44,4 +44,24 @@ The two types of entries (table and directory) look like the same. Only the fiel
     * 0 = 4ko
     * 1 = 4mo
 
+**Note:** Physical addresses in the pages diretcory or pages table are written using 20 bits because these addresses are aligned on 4ko, so the last 12bits should be equal to 0.
+
+* A pages directory or pages table used 1024*4 = 4096 bytes = 4k
+* A pages table can address 1024 * 4k = 4 Mo
+* A pages directory can address 1024 * (1024 * 4k) = 4 Go
+
+#### How to enable pagination?
+
+To enable pagination, we just need to set bit 31 of the `CR0`registry to 1:
+
+```asm
+asm("  mov %%cr0, %%eax; \
+       or %1, %%eax;     \
+       mov %%eax, %%cr0" \
+       :: "i"(0x80000000));
+```
+
+But before, we need to initialize our pages directory with at least one pages table.
+
+