Lenovo PC 300GL Understanding Your Personal Computer 6267, 6277, 6287 - Page 14

Physical and Virtual Memory, Other Types of Memory Management

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memory above the first 1 MB is not written to or read from directly. It is broken into 16 KB pieces called pages, or 64 KB pieces called frames, and is moved in and out of the reserved area as needed. When a page or frame is moved into the reserved area, it can be read from and written to as any other address in conventional memory. Other Types of Memory Management Operating systems such as Microsoft Windows 95, Windows 98, and Windows NT have very sophisticated memory-management systems. These operating systems use a technique called disk swapping or disk paging. If your computer does not have enough memory to meet the needs of your active programs, these operating systems transfer the least-used information from memory to the hard disk to make more memory available. When the information on the hard disk is needed, it is exchanged with other information in memory. Microsoft Windows 95, Windows 98, and Windows NT also use memory in another way. These operating systems assign blocks of memory as virtual DOS machines (VDM). Each VDM runs independently of the others, providing the same function as a separate computer running DOS. With very few exceptions, these operating systems are fully compatible with application programs written for DOS. If you are using any of these operating systems, adding memory can increase the overall performance. Physical and Virtual Memory Physical memory consists of all the addressable memory locations in the computer. Physical memory is used to store such items as the operating system, video data, and instructions and data the computer uses to run programs. Virtual memory is memory that appears to be allocated to application programs. The operating system uses a portion of the hard disk as virtual memory, swapping data and instructions between the hard disk and physical memory. Virtual memory makes multitasking possible. In a multitasking session, the memory requirements of all the programs that might be running in the system at the same time can far exceed the amount of physical memory that is available. The operating system allocates virtual memory to meet the total memory requirements of each program and then manages the available physical memory to meet the actual requirements. Thus, the amount of virtual memory that is allocated can be much greater than the amount of physical memory installed in the computer. 6 Microprocessors and Memory

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memory above the first 1 MB is not written to or read from directly.
It is broken into 16 KB
pieces called
pages
, or 64 KB pieces called
frames
, and is moved in and out of the reserved
area as needed.
When a page or frame is moved into the reserved area, it can be read from
and written to as any other address in conventional memory.
Other Types of Memory Management
Operating systems such as Microsoft Windows 95, Windows 98, and Windows NT have
very sophisticated memory-management systems.
These operating systems use a technique
called
disk swapping
or
disk paging
.
If your computer does not have enough memory to meet
the needs of your active programs, these operating systems transfer the least-used
information from memory to the hard disk to make more memory available.
When the
information on the hard disk is needed, it is exchanged with other information in memory.
Microsoft Windows 95, Windows 98, and Windows NT also use memory in another way.
These operating systems assign blocks of memory as
virtual DOS machines (VDM)
.
Each
VDM runs independently of the others, providing the same function as a separate computer
running DOS.
With very few exceptions, these operating systems are fully compatible with
application programs written for DOS.
If you are using any of these operating systems, adding memory can increase the overall
performance.
Physical and Virtual Memory
Physical memory
consists of all the addressable memory locations in the computer.
Physical
memory is used to store such items as the operating system, video data, and instructions
and data the computer uses to run programs.
Virtual memory
is memory that appears to be allocated to application programs.
The
operating system uses a portion of the hard disk as virtual memory, swapping data and
instructions between the hard disk and physical memory.
Virtual memory makes
multitasking
possible.
In a multitasking session, the memory
requirements of all the programs that might be running in the system at the same time can
far exceed the amount of physical memory that is available.
The operating system allocates
virtual memory to meet the total memory requirements of each program and then manages
the available physical memory to meet the actual requirements.
Thus, the amount of virtual
memory that is allocated can be much greater than the amount of physical memory installed
in the computer.
6
Microprocessors and Memory