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A20 line and XMS manager problem!

Posted on 1997-11-12
Medium Priority
Last Modified: 2013-12-16
hi there,
I have a 486DX Intel processor with 16 RAM. I tried to install win95, I inserted disk 1 and run setup.exe. after the system performance check, my screen showed up the line:

Please wait while Setup initializes.
Error: Unable to ocntrol A20 line!
     XMS Driver not installed.
Setup cannot find a high memory and connot continue.

I also tried to install win3.1, I got same error. what is wrong with my computer?
please give me some hints.

Question by:ny971181
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Expert Comment

ID: 1751733
you need to run himem.sys...edit your config.sys file so that it has a line that says DEVICE=C:\PATH\himem.sys  where PATH is the location of your himem.sys file....probably in C:\DOS  (I've been off 3.1 for TOO long)

Author Comment

ID: 1751734
hi, so many ppl gave me the same answer like you did. but that doesn't work, I tried at least 6 times b4. May I ask what is A20 line? what is xms memory manager? How the xms deal with win 95?
thank you

Expert Comment

ID: 1751735
The XMS memory manager is... HIMEM.SYS. That's why they asked you to put it in CONFIG.SYS
I should ask you to also put, after HIMEM.SYS the following line:
device=c:\path\emm386.exe ram
That _might_ help. If it doesn't, please tell me your E mail so I can send you a util that will check your memory. It might be bad.
If you'd ratther keep your E mail private, send me an E mail at: johnt@mail.club-internet.fr
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Expert Comment

ID: 1751736
The XMS memory manager is... HIMEM.SYS. That's why they asked you to put it in CONFIG.SYS
I should ask you to also put, after HIMEM.SYS the following line:
device=c:\path\emm386.exe ram
That _might_ help. If it doesn't, please tell me your E mail so I can send you a util that will check your memory. It might be bad.
If you'd rather keep your E mail private, send me an E mail at: johnt@mail.club-internet.fr

Expert Comment

ID: 1751737
Oops... Sorry for those 2 comments :)  I should say also that more points would motivate a bit more :)

Author Comment

ID: 1751738
here is the situation:
I copied the system disk form another computer. and did this
format c: /s to my 486 computer. now it has only one file in c:
command.com. I put in win95 disk 1 and setup. Here is where I got problem. I don't have all other files. What should I do now?

Thank you

LVL 25

Accepted Solution

dew_associates earned 60 total points
ID: 1751739
NY: Presuming the other computer is running the same version of Windows 95 that you will be installing on the 486, try this.

On the computer currently running windows 95, create a windows 95 startup disk by clicking, Start, Settings, Control Panel then click the Add/Remove Programs Icon then the Startup Disk tab. Make a startup disk.

Then, using Find, Files and Folders, locate the following files and copy them to the Strtup disk.


Put the Startup disk in the 486 and boot to it.

From the floppy, type EDIT and touch enter.

At the first line, insert the following:


Touch the "alt" key then the down arrow and "save as" this file to the "C" drive on the 486


Repeat the process for an AUTOEXEC.BAT file, but this time insert the following as your first line:


save this as:


Remove the floppy and reboot the system!

Are you using Windows 95 on floppy or CD Rom Disk?

Best regards,


Expert Comment

ID: 1751740
The main part of the solution to the problem consists of making HIMEM work on your computer, as this is essential to both Windows 3.1x in 386 mode and to Windows 95.

HIMEM uses the A20 line to control parts of the computer's RAM. On some older machines the keyboard controller chip is used for that purpose, otherwise it has a dedicated A20 line controller. In case of the latter, you can set it by entering the CMOS setup (usually by pressing the DEL key during startup). In the CMOS setup screen may be an option 'FAST A20 CONTROL', which you can toggle on or off.

Beware: ****ALTERING THE CMOS SETUP IN A WRONG WAY MAY CAUSE YOUR COMPUTER TO BE UNABLE TO START AT ALL!****, so make shure you do not alter anything else unless you know what you are doing.

If that does not help, set the CMOS back to its original state, and procede as follows:

Make a bootable diskette and copy HIMEM.SYS to it.
Create a CONFIG.SYS file on the diskette with the following contents:

Boot the machine with the diskette in place, and observe the screen. The /V switch you added to the HIMEM.SYS means VERBOSE, making the device driver write status messages as it loads. It does not by itself help the problem, but it may make it easier to diagnose.

By editing the line in the CONFIG.SYS, you can try adding different switches, save the changes, and reboot the machine.
Below is an extract from the MS DOS help file, showing some useful switches to use.
For example, you can edit the line to read:

Though this trial-and-error method is quite tedious, chances are that it helps your problem. If not, your processor or motherboard is probably faulty.

Good luck


The information below is cited from Microsoft copyrighted material:

    Specifies whether HIMEM is to take control of the A20 line even if A20
    was on when HIMEM was loaded. The A20 handler gives your computer access
    to the HMA. If you specify /A20CONTROL:OFF, HIMEM takes control of the
    A20 line only if A20 was off when HIMEM was loaded. The default setting
    is /A20CONTROL:ON.

    Specifies what type of computer you are using. Usually, HIMEM can detect
    your computer type successfully; however, there are a few computers that
    HIMEM cannot detect. On such systems, HIMEM uses the default system type
    (IBM AT or compatible). You might need to include the /MACHINE option if
    your computer is a type that HIMEM cannot detect and if HIMEM does not
    work properly on your system by using the default system type.
    Currently, systems that require this option include Acer 1100, Wyse, and
    IBM 7552.
    The value for xxxx can be any of the codes or their equivalent numbers
    listed in the following table.
Code         Number  Computer type
at           1       IBM AT or 100% compatible
ps2          2       IBM PS/2
ptlcascade   3       Phoenix Cascade BIOS
hpvectra     4       HP Vectra (A & A+)
att6300plus  5       AT&T 6300 Plus
acer1100     6       Acer 1100
toshiba      7       Toshiba 1600 & 1200XE
wyse         8       Wyse 12.5 Mhz 286
tulip        9       Tulip SX
zenith       10      Zenith ZBIOS
at1          11      IBM PC/AT (alternative delay)
at2          12      IBM PC/AT (alternative delay)
css          12      CSS Labs
at3          13      IBM PC/AT (alternative delay)
philips      13      Philips
fasthp       14      HP Vectra
ibm7552      15      IBM 7552 Industrial Computer
bullmicral   16      Bull Micral 60
dell         17      Dell XBIOS

If your computer is not on the list, you are not shure which number to use, or the machine number for your computer does not solve the problem, try the machine numbers in the following order: 1, 11, 12, 13, 8, 2 through 7, 9, 10, 14 through 16.

    Directs HIMEM to display status and error messages while loading. By
    default, HIMEM does not display any messages unless it encounters an
    error. You can abbreviate /VERBOSE as /V. (To display status messages
    without adding the /VERBOSE switch, press and hold the ALT key while
    HIMEM starts and loads.)

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