Control Register 4 (CR4) Extensions
3-5
18524C/0—Nov1996
AMD-K5 Processor Technical Reference Manual
3.1.2
4-Mbyte Pages
The TLBs in the 486 and 386 processors support only 4-Kbyte
pages. However, large data structures such as a video frame
buffer or non-paged operating system code can consume many
pages and easily overrun the TLB. The AMD-K5 processor
accommodates large data structures by allowing the operating
system to specify 4-Mbyte pages as well as 4-Kbyte pages, and
by implementing a four-entry, fully-associative 4-Mbyte TLB
which is separate from the 128-entry, 4-Kbyte TLB. From a
given page directory, the processor can access both 4-Kbyte
pages and 4-Mbyte pages, and the page sizes can be intermixed
within a page directory. When the Page Size Extension (PSE)
bit in CR4 is set, the processor translates linear addresses
using either the 4-Kbyte TLB or the 4-Mbyte TLB, depending
on the state of the page size (PS) bit in the page-directory
entry. Figures 3-2 and 3-3 show how 4-Kbyte and 4-Mbyte page
translation work.
Figure 3-2. 4-Kbyte Paging Mechanism
Linear Address
4-Kbyte
Page
Directory
4-Kbyte
Page
Table
4-Kbyte
Page
CR3
0
11
12
21
31
22
Page Directory
Offset
Page Table
Offset
Page
Offset
PDE
PTE
Byte
Summary of Contents for AMD-K5
Page 1: ...AMD K5 Processor Technical Reference Manual TM...
Page 10: ...x AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 24: ...1 4 Overview AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 54: ...2 30 Internal Architecture AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 116: ...4 26 Performance AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 356: ...6 44 System Design AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 380: ...7 24 Test and Debug AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 396: ...A 16 AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 406: ...I 10 Index AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...