DOS Memory Management

From gpu
Revision as of 21:31, 1 October 2025 by Holley78P199070 (talk | contribs) (Created page with "[https://joybuke.neocities.org/ neocities.org] <br>1024 bytes) (KiB) of "standard [https://wiki.la.voix.de.lanvollon.net/index.php/Why_We_Dream_and_What_Happens_When_We_Do Memory Wave Protocol]". The 640 KiB restrict was particular to the IBM Pc and close compatibles; other machines working MS-DOS had different limits, for instance the Apricot Pc could have as much as 768 KiB and the Sirius Victor 9000, 896 KiB. DOS, while allowing laptop customers to take advantage of g...")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

neocities.org
1024 bytes) (KiB) of "standard Memory Wave Protocol". The 640 KiB restrict was particular to the IBM Pc and close compatibles; other machines working MS-DOS had different limits, for instance the Apricot Pc could have as much as 768 KiB and the Sirius Victor 9000, 896 KiB. DOS, while allowing laptop customers to take advantage of giant quantities of low-cost memory and new generations of processors. Since DOS has given method to Microsoft Windows and different 32-bit operating methods not restricted by the original arbitrary 640 KiB limit of the IBM Laptop, Memory Wave managing the memory of a personal pc now not requires the user to manually manipulate inside settings and parameters of the system. The 640 KiB limit imposed great complexity on hardware and software supposed to bypass it; the bodily memory in a machine may very well be organized as a mix of base or Memory Wave conventional memory (including decrease memory), upper memory, high memory (not the same as higher memory), extended memory, and expanded memory, all dealt with in alternative ways.



The Intel 8088 processor used in the unique IBM Computer had 20 tackle traces and so might instantly deal with 1 MiB (220 bytes) of memory. Different areas of this address space were allocated to completely different kinds of memory used for various functions. Starting at the bottom end of the handle space, the Computer had learn/write random access memory (RAM) put in, which was used by DOS and application packages. The first part of this memory was put in on the motherboard of the system (in very early machines, sixty four KiB, later revised to 256 KiB). Additional memory might be added with cards plugged into the enlargement slots; every card contained straps or switches to manage what part of the address house accesses memory and gadgets on that card. On the IBM Pc, all the address space up to 640 KiB was out there for RAM. This a part of the tackle area is called "conventional memory" since it is accessible to all variations of DOS routinely on startup.



Phase 0, the first 64 KiB of standard memory, can also be referred to as low memory space. Usually enlargement memory is ready to be contiguous in the handle area with the memory on the motherboard. If there was an unallocated hole between motherboard memory and the expansion memory, the memory would not be automatically detected as usable by DOS. The upper memory space (UMA) refers to the handle area between 640 and 1024 KiB (0xA0000-0xFFFFF). The 128 KiB area between 0xA0000 and 0xBFFFF was reserved for VGA display screen memory and legacy SMM. The 128 KiB region between 0xC0000 and 0xDFFFF was reserved for system Option ROMs, together with Video BIOS. The sixty four KiB region between 0xE0000 to 0xEFFFF was reserved for BIOS as lower BIOS space. The 64 KiB region between 0xF0000 and 0xFFFFF was reserved for BIOS as upper BIOS space. For instance, the monochrome video adapter memory area ran from 704 to 736 KiB (0xB0000-0xB7FFF). If only a monochrome show adapter was used, the address space between 0xA0000 and 0xAFFFF might be used for RAM, which could be contiguous with the typical memory.



The system BIOS ROMs should be on the higher end of the address area because the CPU beginning tackle is fastened by the design of the processor. The beginning deal with is loaded into the program counter of the CPU after a hardware reset and should have an outlined value that endures after energy is interrupted to the system. On reset or power up, the CPU loads the handle from the system ROM after which jumps to an outlined ROM location to begin executing the system power-on self-test, and eventually load an working system. Since an enlargement card similar to a video adapter, arduous drive controller, or community adapter might use allocations of memory in lots of the upper memory areas, configuration of some combinations of playing cards required careful reading of documentation, or experimentation, to search out card settings and memory mappings that labored. Mapping two gadgets to make use of the identical bodily memory addresses may lead to a stalled or unstable system.



Not all addresses in the upper memory space were utilized in a typical system; unused physical addresses would return undefined and system-dependent data if accessed by the processor. As memory prices declined, software programs equivalent to spreadsheets and pc-aided drafting had been modified to reap the benefits of increasingly physical memory in the system. Virtual memory in the 8088 and 8086 was not supported by the processor hardware, and disk technology of the time would make it too sluggish and cumbersome to be sensible. Expanded memory was a system that allowed software applications to entry extra RAM than instantly visible to the processor's tackle area. The process was a form of financial institution switching. When further RAM was wanted, driver software program would briefly make a piece of expanded memory accessible to the processor; when the info in that piece of memory was updated, another part could possibly be swapped into the processor's tackle area.