Operating System: Memory

Operating System: Memory

0000k device driver free application command.com Ram 640k barrier.

1 - When the MS-DOS is loaded into a PC, different parts of the operating system are associated with different locations
in the range of 1MB of RAM starting at address 0000. The track is a continuous map logically. But the actual physical positions
some addresses can be in different parts of the PC - in the ROM chips that contain the PC's BIOS, the BIOS chip
video card, the RAM chips located on the motherboard of the PC or the memory chips located on the expansion card.

2 - The first byte kilobyte -1024 - manages the interrupt vector (interrupt vectors) set by the BIOS and by
DOS, which can be modified by application programs (application). The vectors indicate the positions of the routines
program in other memory addresses to which these operations should branch out when the various components of
hardware send a specific signal, called interruption.

3 - The next 256 bytes or more contain BIOS data known as flags (flags), used to indicate the
status of the different conditions of the internal system. Also in this area there is a keyboard buffer (keyboard buffer) of 16 bytes
in which are stored keystrokes, while the PC is temporarily occupied with other tasks, to be
processed next.

4 - The remainder of the RAM up to 640K is called conventional memory. This is the RAM in which the COMMAND.COM, drivers
devices, memory-resident programs and applications are usually loaded. The memory managers
as QEMM-386 or HIMEM.SYS accompanying the MS-DOS 5.0, enable the memory remapping so that drivers
devices (device drivers), the memory-resident programs (memory resident programs) and the MS-DOS 5.0, part of the
COMMAND.COM, can be loaded into high memory above the 640KB, reserved for application programs (application). If
such memory managers are not used, the COMMAND.COM is loaded in the highest memory address
conventional, which can be replaced by any application that needs memory.

5 - Above the conventional memory is high memory, part of which is reserved by the BIOS for multiple boards
Video (display adapter) and other cards such as LAN (token-ring adapter) and hard drive controllers
(Disk controller). The memory managers can remap the areas for these peripherals in order to create areas
more memory available, in which they could charge other device drivers and programs.

1024k display adapter Bios Disk controller token-ring adapter memory resident program.

6 - Approximately the last 64KB of high memory are reserved for BIOS ROM chips contained in the PC. A system
IBM, there is also a simplified code programming, the BASIC ROM.

7 - Although the MS-DOS can directly address only 1024KB, some special schemes allow memory addressing
1024KB above to be used as extended or expanded memory. (The extended RAM can be used only in
Intel 80286 or later.) Under DOS, extended or expanded memory can not be used to manage
program codes, but can manage data.

Note - The DOS services are always available through the BIOS extensions made by the operating system. Beyond
addition, the DOS commands like DIR, which are part of COMMAND.COM, are another part of the operating system commands.
And what we think is simple DOS commands (such as FORMAT, CHKDSK and MEM) are actually utilities. They only
are available if they are on disk in the current directory or any directory in the list of paths (path) of the PC.

Source: Evolution of Computers