Memory Allocations; Table 3-5. Conventional Memory Map - Dell Latitude XPiCD Reference Manual

Table 3-4. IRQ Line Assignments
IRQ Line Used/Available
IRQ12 Generated by the keyboard controller
to indicate that the output buffer of the
integrated trackball or external PS/2
mouse is full
IRQ13 Not available
IRQ14 Generated by the hard-disk drive to
indicate that the drive requires the
attention of the microprocessor
IRQ15 Reserved for the CD-ROM drive
NOTE: For the full name of an abbreviation or acronym used
in this table, see the Glossary in the online System User's
Guide.

Memory Allocations

A microprocessor and programs operating under
MS-DOS (real-mode operation) can address only
1 megabyte (MB) (1024 kilobytes [KB]) of system mem-
ory. This area is divided into conventional memory
(sometimes called base memory) and upper memory. All sys-
tem memory above this 1 MB is called extended memory and
cannot be directly addressed by MS-DOS–based programs
without the aid of some special memory-managing software.
Table 3-5 provides a map of the conventional memory area.
When the microprocessor or a program addresses a location
within the conventional memory range, it is physically
addressing a location in main memory, which is the only main
memory it can address under MS-DOS.
3-16 Dell Latitude XPi CD Reference and Troubleshooting Guide
(Continued)
Address Range
00000h–003FFh
00400h–004FFh
00500h–005FFh
00600h–0FFFFh
10000h–1FFFFh
20000h–2FFFFh
30000h–3FFFFh
40000h–4FFFFh
50000h–5FFFFh
60000h–6FFFFh
70000h–7FFFFh
80000h–8FFFFh
90000h–9FBFFh
NOTE: For the full name of an abbreviation or acronym
used in this table, see the Glossary in the online System
User's Guide.
Table 3-6 provides a map of the upper memory area. Some of
these addresses are dedicated to various system devices, such
as the system/video basic input/output system (BIOS). Others
are available for use by expansion cards and/or an expanded
memory manager (EMM). When the microprocessor or a pro-
gram addresses a location within the upper memory area, it is
physically addressing a location within one of these devices.

Table 3-5. Conventional Memory Map

Use
Interrupt vector table
BIOS data area
MS-DOS and BASIC work area
User memory
User memory
User memory
User memory
User memory
User memory
User memory
User memory
User memory
User memory