๐๐ต๐ฎ๐ฝ๐๐ฒ๐ฟ ๐ฎ-๐ฏ: Protected Mode Memory Addressing Flashcards
where Windows operates
protected mode
selects a descriptor from a descriptor table
selector
describes the memory segmentโs location, length, and access rights
descriptor
contain segment definitions that apply to all programs
global descriptors
another name for global descriptors
system descriptors
usually unique to an application
local descriptors
another name for local descriptors
application descriptors
starting location of the memory segment
base address
operates on 16-bit environment
DOS
operates on WIN32
Windows applications
Large bit / Intel calls it the 64-bit
L bit
Granularity bit
G bit
segment limit when G = 0
00000H to FFFFFH
value of the limit when G = 1
multiplied by 4K bytes
The 32-bit environment that Windows applications use
WIN32
AV bit = 1
Available
AV bit = 0
Not Available
D bit = 0
16-bit Instructions
D - bit = 1
32-bit Instructions
controls access to the protected mode segment
Access rights byte
selects either the global descriptor table or the local descriptor table
TI bit
requests the access privilege level of a memory segment
requested privilege level
privilege level for ring 0; for kernel and driver programs
privilege level 00
privilege level for ring 3; for applications
privilege level 11
GDTR meaning
Global descriptor table register
IDTR meaning
Interrupt descriptor table register
what does GDTR & IDTR contain
base address of the descriptor table and its limit
limit of descriptor table
16 bits
maximum table length
64K bytes
LDTR meaning
Local descriptor table register
TR meaning
Task Register
Holds a selector which accesses a descriptor that defines a procedure or application program
Task Register / TR
