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Why is resident portion of DOS loaded in lower memory?
By using this free memory pointer scheme, DOS can protect the memory in use by the resident program. To use TSRs effectively, you need to organize your code and data so that the resident portions of your program loads into lower memory addresses and the transient portions load into the higher memory addresses.
Does DOS have virtual memory?
Virtual 8086 mode, introduced with the Intel 80386, allows the A20 wrap-around to be simulated by using the virtual memory facilities of the processor: physical memory may be mapped to multiple virtual addresses, thus allowing that the memory mapped at the first megabyte of virtual memory may be mapped again in the …
How much RAM did MS-DOS use?
DOS was originally designed for the Intel 8086/8088 processor and therefore could only directly access a maximum of 1 MB of RAM. Due to PC architecture only a maximum of 640 KB (known as conventional memory) is available as the upper 384 KB is reserved.
What is meant by upper memory area and high memory area?
Short for Upper Memory Area, UMA is the area of RAM between 640 KB and 1,024 KB (1 MB) in legacy computers, that is made available to user applications as RAM. In DOS based systems, memory is split into five areas: conventional memory; upper memory; high memory; extended memory; and expanded memory.
What is a TSR process?
A terminate-and-stay-resident program (commonly TSR) is a computer program running under DOS that uses a system call to return control to DOS as though it has finished, but remains in computer memory so it can be reactivated later. TSRs are used only in DOS, not in Windows.
What is a TSR virus?
A terminate and stay resident (TSR) virus is one that stays active (resident) in memory after the. application has terminated Page 4 TSR viruses can be boot sector infectors or executable infectors. Both the Brain and Jerusalem viruses are TSR viruses.
What does Himem SYS do?
SYS is a DOS device driver which allows DOS programs to store data in extended memory according to the Extended Memory Specification (XMS). The memory beyond the first 1 MB of address space is required by Windows 9x/Me in order to load, therefore these versions of Microsoft Windows required HIMEM. SYS . …
What is the difference between expanded and extended memory?
The expanded memory requires hardware and/or software that maps the expanded memory to a piece of address space, in what is called a “page frame”. Extended memory can be used as expanded memory by using software and the 80286 or 80386 chips to “remap” it to the lower 1MB.
How can I load DOS into high memory?
The second line tells DOS to load itself into high memory and enable the use of upper memory blocks. But to take full advantage of HIMEM.SYS, you also need to load its counterpart, EMM386.EXE. Here’s the most generally useful config.sys line to enable it: This loads EMM386 and tells it to emulate EMS memory using XMS memory.
How to move 64K of DOS out of conventional memory?
Do use DOS=HIGH,UMB. This moves 64K of DOS out of conventional memory, and it doesn’t use any upper memory either! Do use DEVICE=C:\\DOS\\HIMEM.SYS. DOS can’t move anything out of conventional memory without it. Do use EMM386.EXE. This allows you to use the upper memory area.
When did DR DOS use the high memory area?
The next stage in the evolution of DOS was for the operating system to use upper memory blocks (UMBs) and the high memory area (HMA). This occurred with the release of DR DOS 5.0 in 1990.
What’s the difference between DOS and upper memory?
We clearly see that DOS manages two different memory blocks, the conventional and the upper memory block. I think the best would now be to explain those terms now. again some history: The original PC in 1980 had a 8088/8086 which could handle 1MB of memory.