DOS Memory Administration > 자유게시판

1024 bytes) (KiB) of "conventional memory". The 640 KiB restrict was particular to the IBM Laptop and shut compatibles; other machines working MS-DOS had completely different limits, for instance the Apricot Pc may have as much as 768 KiB and the Sirius Victor 9000, Memory Wave Program 896 KiB. DOS, while permitting laptop customers to make the most of large amounts of low-cost memory and new generations of processors. Since DOS has given solution to Microsoft Home windows and different 32-bit working programs not restricted by the unique arbitrary 640 KiB limit of the IBM Pc, managing the memory of a private pc no longer requires the person to manually manipulate inside settings and parameters of the system. The 640 KiB restrict imposed nice complexity on hardware and software supposed to circumvent it; the physical memory in a machine might be organized as a combination of base or conventional memory (including decrease memory), higher memory, high memory (not the identical as higher memory), extended memory, and expanded memory, all dealt with in different ways.

The Intel 8088 processor used in the original IBM Pc had 20 handle traces and so could directly tackle 1 MiB (220 bytes) of memory. Completely different areas of this deal with house had been allotted to totally different kinds of memory used for various functions. Starting at the bottom end of the address area, the Pc had learn/write random access memory (RAM) put in, Memory Wave which was used by DOS and software applications. The first part of this memory was installed on the motherboard of the system (in very early machines, 64 KiB, later revised to 256 KiB). Extra memory may very well be added with playing cards plugged into the enlargement slots; each card contained straps or switches to regulate what a part of the handle space accesses memory and gadgets on that card. On the IBM Computer, all of the tackle area up to 640 KiB was available for RAM. This part of the tackle house is called "conventional memory" since it is accessible to all versions of DOS routinely on startup.

Segment 0, the first sixty four KiB of conventional memory, can be known as low Memory Wave Program area. Usually enlargement memory is about to be contiguous in the deal with area with the memory on the motherboard. If there was an unallocated gap between motherboard memory and the growth memory, the memory wouldn't be robotically detected as usable by DOS. The upper memory area (UMA) refers back to the tackle 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 64 KiB region between 0xE0000 to 0xEFFFF was reserved for BIOS as decrease BIOS area. The sixty four KiB area between 0xF0000 and 0xFFFFF was reserved for BIOS as higher BIOS area. For example, the monochrome video adapter memory space ran from 704 to 736 KiB (0xB0000-0xB7FFF). If solely a monochrome show adapter was used, the address house between 0xA0000 and 0xAFFFF could possibly be used for RAM, which can be contiguous with the standard memory.

The system BIOS ROMs have to be at the higher finish of the tackle house because the CPU beginning deal with is fixed by the design of the processor. The beginning tackle is loaded into this system counter of the CPU after a hardware reset and will need to have a defined worth that endures after power is interrupted to the system. On reset or energy up, the CPU loads the tackle from the system ROM after which jumps to a defined ROM location to begin executing the system energy-on self-check, and finally load an working system. Since an growth card reminiscent of a video adapter, exhausting drive controller, or community adapter could use allocations of memory in most of the higher memory areas, configuration of some combos of playing cards required cautious reading of documentation, or experimentation, to seek out card settings and memory mappings that labored. Mapping two units to make use of the same physical memory addresses might result in a stalled or unstable system.

Not all addresses in the upper memory area were used in a typical system; unused physical addresses would return undefined and system-dependent knowledge if accessed by the processor. As memory costs declined, application programs such as spreadsheets and pc-aided drafting were modified to make the most of increasingly more physical memory within the system. Virtual memory within the 8088 and 8086 was not supported by the processor hardware, and disk expertise of the time would make it too sluggish and cumbersome to be practical. Expanded memory was a system that allowed software programs to entry extra RAM than immediately seen to the processor's address area. The process was a form of financial institution switching. When additional RAM was needed, driver software program would temporarily make a piece of expanded memory accessible to the processor; when the info in that piece of memory was up to date, one other part might be swapped into the processor's tackle area.