Specifications

Computer Architecture and Maintenance (G-Scheme-2014)
developed by AST, Quadram and Ashton-Tate is known as EEMS (Extended EMS).
EEMS enables programs to use extra memory for code as well as for data. The most
recent version of EMS (created in 1987) is known as EMS 4.0 or LIM 4.0, LIM being the
initials of the three companies that developed the specification: Lotus, Intel, and
Microsoft. EMS 4.0 raises the available amount of memory to 32MB.
Expanded memory relies on technical trick known as paging. Paging involves
accessing of large memory by swapping it in 16KB chunks or blocks in and out of 64KB
memory window. This window is placed between unused memory space from 640KB
to 1MB.Expanded memory is inefficient for the program code and is normally used for
the data. This memory unlike conventional or extended this memory cannot be directly
addressed by the processor.
Expanded memory is slow and clumsy for the system to use and generally obsolete
(outdated) now days. But some of the antique software still require EMS memory. 386
and higher systems can create expanded memory out of extended memory out of
extended memory by using a driver called “EMM386.EXE”. This software was
designed with 8-bit system because they do not have capability to access extended
memory. This software is load through the Autoexec.bat file.
Until the release of Microsoft Windows 3.0 in 1990, expanded memory was the
preferred way to add memory to a PC. The alternative method, called extended memory,
was less flexible and could be used only by special programs such as RAM disks.
Windows 3.0 and all later versions of Windows, however, contain an extended memory
manager that enables programs to use extended memory without interfering with one
another. In addition, Windows can simulate expanded memory for those programs that
need it (by using the EMM386.EXE driver).
Main uses extended memory are:
RAM-disks
A RAM-disk is a chunk of semiconductor memory that behaves like an ordinary disk
but is extremely fast. It also loses its data instantly once power is turned off but is great
for temporary files such as index files, extracted data from Lotus to be imported into
another application etc. Example: VDISK.SYS, supplied as part of DOS 3.x.
To create a RAM-disk, add one line in your config.sys such as DEVICE =
\DOS\VDISK.SYS 256 /E. This will look in the DOS subdirectory for the driver, create
a 256 kB RAM-disk. The /E parameter will place it into the extended memory.
Prepared By – Prof. Manoj.kavedia (9860174297 – 9324258878 ) (www.kavediasir.yolasite.com)
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