Extended memory is additional memory available on DOS systems, typically over 1 MB, supported by certain microprocessors. It’s managed through an API and allows for more efficient allocation of memory resources. Expanded memory is configured to meet a specific standard, while extended memory is not. Newer processors make expanded memory obsolete, allowing for larger amounts of memory and more tasks to be handled.
Extended memory refers to any amount of memory available for use on the main storage inherent in most DOS systems. In most cases, this means that any memory over 1 megabyte (MB) supported by DOS will be considered extended memory. Memory of this type is supported by the use of certain types of microprocessors that allow for loading and accessing extended memory. Along with the extended form of memory, many systems are also capable of supporting so-called expanded memory.
One major difference between extended and expanded memory is that expanded memory is configured to meet a specific published standard known as EMS. This standard works with DOS to allow access to additional memory and make it possible to use that memory for certain tasks. Conversely, extended memory must not use EMS or any particular published standard. Instead, the ability to use that additional memory via the microprocessor is managed with the use of an application programming interface that allows communication between standard and extended memory.
The extended memory feature allows a system to allocate memory resources more efficiently. As part of the allocation, the processor can determine when standard memory is insufficient to handle certain tasks and use a portion of the added memory resources to complete necessary steps in the task sequence. For end users, the perception is that total memory is insufficient to drive the required functions, with no real need to distinguish whether the resources involved are from standard memory or from extended memory. The end result, a completed task, is always the same.
Over time, extended memory has become more common than using the expanded memory approach. This is because newer systems use more powerful processors which makes the need to use expanded memory obsolete. As a result, more powerful processors can support installing significantly more memory, which in turn allows the system to handle more tasks at once, without negatively impacting overall system efficiency. The ability to access ever larger amounts of memory has led end users to perform tasks on desktop and laptop systems that would have been impossible a decade ago. As the use of computers in everything from business activities to access to entertainment options continues to grow, processors capable of handling large amounts of memory will be developed.
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