THE MEMORY SYSTEM:
The memory system is classified into three regions -
1. TPA (Transient Program Area)
2. Systems Area
3. XMS (Extended Memory System)
In the 8086 or 8088, The TPA and the systems area exist, but the XMS is absent. The TPA contains 640K bytes of memory and the systems area, 384K bytes, for a total memory of 1M bytes.
Of the three memory divisions, theTPA is of most functional importance. Info about the TPA is discussed here.
The TPA:
The Transient Program Area holds the DOS ( Disk Operating System) and other programs which are responsible for a computer's functionality. The Windows XP version of MSDOS leaves around 628K bytes of memory in the TPA for applications and other programs. The earlier versions left only 530K bytes of memory. A Typical DOS map shows how many areas are present in the TPA, and their memory locations (via hexadecimal notation). The memory map shows regions in the TPA specified by Interrupt vectors, BIOS and DOS Communications area, the IO.SYS program, device drivers, COMMAND.COM, the MSDOS program and free TPA space.
The BIOS and DOS communications areascontain data used by programs to access the I/O devices and other internal features of a computer. The BIOS program is seen as a collection of programs which operate many of the I/O systems, and these are generally stored in ROM(read only memory) or a flash drive. The BIOS, DOS programs are accessed by the interrupt vectors.
The 8086 microprocessor also has a program called IO.SYS program in the TPA. This program loads into the TPA from the disk whenever the DOS starts. It contains sets of programs which allow the usage of the I/O devices, keyboard, mouse, video graphics etc.
Drivers are programs which lets the microprocessor control the devices like the mouse, keyboard etc. some programs or applications need special drivers of their own too.
Another important program is the COMMAND.COM. This controls the operation of the computer from the keyboard when operated in DOS mode.
It is the COMMAND.COM program which comes into play when we type something into the "run" window or the cmd prompt.
(to be continued...)
The memory system is classified into three regions -
1. TPA (Transient Program Area)
2. Systems Area
3. XMS (Extended Memory System)
In the 8086 or 8088, The TPA and the systems area exist, but the XMS is absent. The TPA contains 640K bytes of memory and the systems area, 384K bytes, for a total memory of 1M bytes.
Of the three memory divisions, theTPA is of most functional importance. Info about the TPA is discussed here.
The TPA:
The Transient Program Area holds the DOS ( Disk Operating System) and other programs which are responsible for a computer's functionality. The Windows XP version of MSDOS leaves around 628K bytes of memory in the TPA for applications and other programs. The earlier versions left only 530K bytes of memory. A Typical DOS map shows how many areas are present in the TPA, and their memory locations (via hexadecimal notation). The memory map shows regions in the TPA specified by Interrupt vectors, BIOS and DOS Communications area, the IO.SYS program, device drivers, COMMAND.COM, the MSDOS program and free TPA space.
The BIOS and DOS communications areascontain data used by programs to access the I/O devices and other internal features of a computer. The BIOS program is seen as a collection of programs which operate many of the I/O systems, and these are generally stored in ROM(read only memory) or a flash drive. The BIOS, DOS programs are accessed by the interrupt vectors.
The 8086 microprocessor also has a program called IO.SYS program in the TPA. This program loads into the TPA from the disk whenever the DOS starts. It contains sets of programs which allow the usage of the I/O devices, keyboard, mouse, video graphics etc.
Drivers are programs which lets the microprocessor control the devices like the mouse, keyboard etc. some programs or applications need special drivers of their own too.
Another important program is the COMMAND.COM. This controls the operation of the computer from the keyboard when operated in DOS mode.
It is the COMMAND.COM program which comes into play when we type something into the "run" window or the cmd prompt.
(to be continued...)
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