Summary

Chapter 5: Fundamental Operating Systems 119Table 5-1Memory ManagementMemory TypeConventionalUpperExtendedLogical Memory Allocation0 to 640 KB640 KB to 1 MB1 MB to the maximum amount of RAM installedThe sections that follow describe these modes of operation in greater detail.Real ModeA CPU that operates in real mode can only execute one program at a time, and it can onlyaddress 1 MB of system memory at a time. Although all modern processors have real modeavailable, it is only used by DOS and DOS applications or by 16-bit operating systems,such as Windows 3.x. In real mode, when an application creates an error, the entire computercan be affected because the program has direct access to memory. This can cause thecomputer to stop responding, restart, or shut down due to corruption of the memory space.Table 5-2 is a chart of some common DOS commands that can still be used in modern operatingsystems, such as Windows XP.Table 5-2CommandHELPDIRATTRIBEDITCOPYXCOPYFORMATMDCDRDCommon DOS CommandsFunctionProvides command-line helpDisplays the contents of a directoryChanges the attributes of a file to indicate a read-only, archive,system, or hidden fileOpens a file for editingCopies a fileCopies files and subdirectoriesFormats a diskMakes a new directoryChanges to a specified directoryRemoves a directory