Error: "Unable to control A20 line" when starting Ghost.exe
| Situation: | When you run Ghost.exe, you see the message "Causeway error 07: unable to control A20 line." |
| Solution: | This message indicates a problem with the Himem.sys file. If the problem occurs after you "warm boot" the computer, it is usually eliminated by a "cold boot." Before trying any of the following solutions, turn off the computer, wait 30 seconds, and then turn the computer on again. Turning off the computer flushes memory, which might allow the Himem.sys file to load correctly. NOTE: For a detailed explanation of Himem.sys and warm and cold boots, see "Technical explanation of the messages" later in this document. This problem is most often caused by the computer's CPU using a nonstandard type of memory management. To resolve this problem, add the lines Device=A:\Himem.sys and Set DOS16M=2 to the Config.sys and Autoexec.bat files, respectively. See the section "How to edit the Config.sys and Autoexec.bat startup files" later in this document. If adding those lines to the startup files does not resolve the problem, check the following possibilities:
How to edit the Config.sys and Autoexec.bat startup files This procedure modifies the Config.sys and Autoexec.bat files to accommodate different types of memory handling used by the CPU. Since a variety of memory handling methods are in use, you may need to repeat this procedure several times to find the modification necessary for the particular CPU on your computer, as described in Step 9. To modify the startup files to accommodate different types of memory handling:
If the problem is still not resolved If none of these procedures resolved the problem, there may be physical damage to some component of the computer, such as a bad memory chip. Resolution of such issues is beyond the scope of this document. Technical explanation of A20 messages Himem.sys is a DOS program that enables access to the first 64 KB of extended memory, called "high memory." Although Windows is an operating system, it needs this file because Windows 3.x, Windows 95, and Windows 98 are not "standalone" operating systems. They require the Disk Operating System (DOS) to load and run. During computer startup, the computer first starts up in DOS. Once DOS is loaded and the computer has access to high memory, Windows can then load. If the computer does not have access to high memory, Windows cannot load and the computer will display A20 messages. The number A20 refers to the "line" of the CPU that must be enabled in order for Himem.sys to access the high memory area. The A20 error occurs when the A20 line is not enabled. Warm boot A "warm boot" means restarting the computer without first turning off the power. In DOS, a computer can be warm booted by using the Reset button or by pressing Ctrl+Alt+Del. Cold boot A "cold boot" means starting the computer by turning on the power. Generally, after turning off the power, wait 5 to 30 seconds before turning on the power again. This allows time for the hard disk to fully power down before restarting it and time for old information to "drain" from the computer. |
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