For example the c standard library provides an

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 10.7. CASE STUDY: THE PENTIUM/LINUX MEMORY SYSTEM 511 Figure 10.25(a) shows the format of a PDE. When È ½ (which is always the case with Linux), the address field contains a 20-bit physical page number that points to the beginning of the appropriate page table. Notice that this imposes a 4-KB alignment requirement on page tables. Figure 10.25(b) shows the format 31 12 11 9 8 7 6 5 4 3 2 1 0 Page table physical base addr unused G PS A CD WT U/S R/W P=1 Field P R/W U/S WT CD A PS G PT base addr Description page table is present in physical memory (1) or not (0) read-only or read-write access permission user or supervisor mode (kernel mode) access permission write-through or write-back cache policy for this page table cache disabled (1) or enabled (0) has the page been accessed? (set by MMU on reads and writes, cleared by software) page size 4K (0) or 4M (1) global page (don’t evict from TLB on task switch) 20 most significant bits of physical page table address (a) Page Directory Entry (PDE). 31 12 11 9 8 7 6 5 4 3 2 1 0 Page physical...
View Full Document

This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

Ask a homework question - tutors are online