A computer capable of running a multi-tasking system may have to deal with widely varying demands for memory. At some times, no users may be logged on and the only tasks running are the kernel and possibly a backup process. At other times, ten or more users may all be carrying out complex operations which demand lots of memory.
Microsoft Windows versions 3.x provided a protected mode graphical operating environment that ran existing MS-DOS applications and allowed Windows applications to break the 640K barrier. There are three types of memory that Windows 3.x can use or provide (conventional, extended, and expanded).
Conventional memory is the first 640K of memory in your machine. MS- DOS has a limit of 1024K of addressable memory (conventional memory plus the UMA), and all MS-DOS applications must run within this conventional memory. All Windows 3.x operating modes share this limitation for running MS-DOS applications, but standard and 386 enhanced modes break the 640K limitation for running Windows applications. Windows 3.x enhanced mode can create multiple virtual MS- DOS machines (Memory).
Between the top of conventional memory at 640K and the start of extended memory at 1024K lies the 384K UMA. This area does not contain physical memory. Mapped into the 384K
UMA are the system BIOS (basic input/output system) ROM chips and the display adapter memory. When you install other accessory cards, such as network adapters, they may also occupy space within the 384K UMA.
Extended memory is the simplest type of add-on memory to understand. It is also the type of memory used by Windows 3.x running in either standard or 386 enhanced operating mode. Extended memory is a seamless continuation of the original 1 MB address space on 80286 and 80386 computers. Extended memory always starts exactly at 1024K, where the 384K UMA ends. There are no exceptions (Memory).
Windows 3.1 used swapping as part of it’s memory managment scheme. The system supported concurrent execution of processes in memory. If a new process is loaded and there is insufficient main memory an old process is swapped to disk. This swapping process is called virtual memory. Windows 3.1 used virtual memory, but since is was a 16 bit system is didn’t use is as effectively as Windows 95.
Users of Windows 95 didn’t have to worry about conventional, extended, or expanded memory…memory was installed and just used by the system. This made life easier for the user. Windows 95 uses a 32-bit code, which can move data at higher speed than the 16-bit code used by previous versions of Windows (Windows 3.1, 3.11, etc.). As a result, Windows 95 memory management is more efficient, and printing and other tasks finish faster. At least in theory, the...