Extended memory is memory located past the first megabyte of the address space. Only 286s and up support extended memory. With the minor exception of the HMA (see below), it is only addressable by applications run in real mode. DOS applications make use of this memory to store data, but not to execute code.
What do you mean by extended memory and expanded memory?
Memory addresses greater than or equal to one megabyte are called extended memory. Expanded memory is addressed from within the lower 1MB space, usually above 640K. It is sometimes up to 64K of real addresses but this is just a small portion of the whole expanded memory, which can be very large.
How does EMM386 work?
EMM386. EXE can map memory into unused blocks in the upper memory area (UMA), allowing device drivers and TSRs to be “loaded high”, preserving conventional memory. EXE version appeared in MS-DOS 5.0 in 1991. Just as the other expanded memory managers, EMM386 uses the processor’s virtual 8086 mode.
What is the purpose of Himem Sys?
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.
What’s the difference between expanded and extended memory?
Expanded memory is addressed from within the lower 1MB space, usually above 640K. Extended memory can be used as expanded memory by using software and the 80286 or 80386 chips to “remap” it to the lower 1MB.
What is extended memory in SAP?
SAP extended memory is the core of the SAP memory management system. Each SAP work process has a part reserved in its virtual address space for extended memory. This means the address space uses the paging file or uses the swap space of the operating system as background memory.
What is meant by extended memory?
Extended memory, also known as XMS (eXtended Memory Specification) is a technology that enables capacity above the 640KB standard MS-DOS limit of main memory. Prior to XMS, expanded memory was used to increase the 640KB upper limit of DOS to 1MB using a gated memory card riser.
What is called extended memory?
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems.
What is expanded memory in computer?
Expanded Memory Specification (EMS), or expanded memory, is a technique for utilizing more than 1MB of main memory in DOS -based computers. The limit of 1MB is built into the DOS operating system. The upper 384K is reserved for special purposes, leaving just 640K of conventional memory for programs.
What is the physical memory range called as low memory or conventional memory?
Segment 0, the first 64 KB of conventional memory, is also called low memory area. Normally expansion memory is set to be contiguous in the address space with the memory on the motherboard.
What is config sys file?
CONFIG. SYS is a configuration file on DOS systems. It is a text file that contains the settings and commands to load drives in a DOS system. This is a primary configuration file for OS/2 and DOS OS. This file was introduced in DOS and is replaced for 32-bit Windows versions with CONFIG.
Where is Himem SYS located?
Note: While this file is only located in the Windows directory, it may also to be located in the root or DOS directory. If when typing any of the above commands you receive a prompt that the file already exists, ensure to overwrite it.
What is extended memory specification?
The term is mainly used under the DOS and Windows operating systems. DOS programs, running in real mode or virtual x86 mode, cannot directly access this memory, but are able to do so through an application programming interface called the eXtended Memory Specification (XMS).
What is expanded-memory manager?
An expanded-memory board, being a hardware peripheral, needed a software device driver, which exported its services. Such a device driver was called expanded-memory manager. Its name was variable; the previously mentioned boards used REMM.SYS (AST), PS2EMM.SYS (IBM), AEMM.SYS (AT) and EMM.SYS (Intel) respectively.
Why do we use extended memory in drivers?
Because of the available support for expanded memory in popular applications, device drivers were developed that emulated expanded memory using extended memory. Later two additional methods were developed allowing direct access to a small portion of extended memory from real mode.
How does the memory management API work?
This API is implemented by a driver (such as HIMEM.SYS) or the operating system, which takes care of memory management and copying memory between conventional and extended memory, by temporarily switching the processor into protected mode.
