Re: Problems installing Debian on a 486
On Tue, Mar 23, 1999 at 03:03:28PM -0800, Alan Bailward wrote: other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... [snip] The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Could it be that the kernel on the rescue disk was compiled for 586+? Could that be causing it? I'm grasping I know, but... :) alan, out on a limb. The A20 line has something to do with working around a bug in memory addressing that first showed up in 286's I think. I don't really know much about it, but on my 486, their is an option in the BIOS to set the line. You might try changing this option in the Bios at boot and see if it helps. Gerald
Re: Problems installing Debian on a 486
On Wed, 24 Mar 1999, G. Crimp wrote: The A20 line has something to do with working around a bug in memory addressing that first showed up in 286's I think. I don't really know much about it, but on my 486, their is an option in the BIOS to set the line. You might try changing this option in the Bios at boot and see if it helps. The original 8088 had 20 address lines called A0 through A19. This allowed it to directly access 1024k of memory. (It was split 640k/384k as RAM/ROM. It could have been worse, my understanding is that the original plan was to split it half and half. Oh, and the 8086 had 19 address lines called A1 through A19. I digress.) Anyway, on the 8086's and 8088's you could access the bottom 65520 bytes of RAM by setting the segment register to the very top of RAM and using an offset larger than the amount of RAM above the start of the segment register. Anyway, along comes the 80286. It has, in effect, 24 address lines (A0 through A23) for a total allowed memory of 16,384k. That broke those programs that relied upon the memory wrapping around. Since they all ran under DOS and since DOS was limited to 1024k, PC manufacturers put a control in which would not pass the A20 line through to the RAM, which had the effect of simulating the behavior of the 8086/8. That's what the A20 gate is about. You could run some DOS programs with the A20 gate disabled that you couldn't run with it enabled. You, of course, want to run a protected-mode operating system, where relying on tricks like that simply cannot work. Since many people also wanted to run protected mode software, (to do things like loadhi and with extended memory and suchlike) the mboard manufacturers made that gate configurable. That's the whole story, to the best of my knowledge. -- Jonathan Guthrie ([EMAIL PROTECTED]) Brokersys +281-895-8101 http://www.brokersys.com/ 12703 Veterans Memorial #106, Houston, TX 77014, USA
Re: Problems installing Debian on a 486
There is one more thing. On 286's and above when in real mode, if the segment register is set to 0x then the address's above 0x will overflow into address bit a20 giving access to an additional 65k(-16 bytes) of memory in real mode. This was known as 'hi-mem' access and dos 4.0 and above used this trick. (meant turning that a20 gate on to allow a20 through). === Amateur Radio, when all else fails! http://www.qsl.net/wa2mze Debian Gnu Linux, Live Free or . _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com
Re: Problems installing Debian on a 486
Matthew Gregan wrote: At 15:03 1999-03-23 -0800, Alan Bailward wrote: other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... I can't answer your question, BUT I can tell you this: This is to do with protected mode, and the keyboard. the only other time that I know of this occuring is occasionally with himem.sys (xx-DOS) on older hardware. If it can't do this, HIMEM.SYS uses some other handler - not sure how linux is meant to do this. frankie [snip] The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Could it be that the kernel on the rescue disk was compiled for 586+? Could that be causing it? I'm grasping I know, but... :) These are the rescue disks from the debian-slink disk-i386 dir... I'm pretty sure they're not using a kernel for 586+ architecture... I should also mention that someone suggested I try the tecra rescue disk. I did that, and had no luck... I get the same message, so now I'm really stumped, having read the readme for the tecra disk I would have though that'd fix the problem. Thanks again... -- Matthew Gregan[EMAIL PROTECTED] -- Unsubscribe? mail -s unsubscribe [EMAIL PROTECTED] /dev/null -- Confession is good for the soul only in the sense that a tweed coat is good for dandruff. --Peter de Vries http://www.skunkpussy.freeserve.co.uk - Drum'n'Bass music, samples and links. ICQ://25576761begin:vcard n:;Frankie x-mozilla-html:TRUE url:http://www.skunkpussy.freeserve.co.uk adr:;;;Birmingham;;;UK version:2.1 email;internet:[EMAIL PROTECTED] title:Mr x-mozilla-cpt:;-8160 fn:Frankie end:vcard
Re: Problems installing Debian on a 486
Subject: RE: Problems installing Debian on a 486 Date: Wed, Mar 24, 1999 at 11:43:47AM +1200 In reply to:Matthew Gregan Quoting Matthew Gregan([EMAIL PROTECTED]): At 15:03 1999-03-23 -0800, Alan Bailward wrote: other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... [snip] The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Could it be that the kernel on the rescue disk was compiled for 586+? Could that be causing it? I'm grasping I know, but... :) These are the rescue disks from the debian-slink disk-i386 dir... I'm pretty sure they're not using a kernel for 586+ architecture... I should also mention that someone suggested I try the tecra rescue disk. I did that, and had no luck... I get the same message, so now I'm really stumped, having read the readme for the tecra disk I would have though that'd fix the problem. Thanks again... -- Matthew Gregan[EMAIL PROTECTED] Just had a light bulb go on. I may be out in left field but I seem to remember a bios option for the A20 gate in my old 486DX50. You might give that a look. HTH -- ... one of the main causes of the fall of the Roman Empire was that, lacking zero, they had no way to indicate successful termination of their C programs. -- Robert Firth ___ Wayne T. Topa [EMAIL PROTECTED]
Problems installing Debian on a 486
Hi everyone. I've got 2 old 486 machines here that I'm trying to install slink onto. One of them is a Compaq Deskpro 486/33M and the other is built out of off the shelf parts. I've managed to install onto the Compaq machine with no problems whatsoever, but when I try to boot the rescue/install disk on the other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... I don't know what the problem is, so I was hoping someone could help me out. I've tried turning off both processors caches in the BIOS, but that made no difference... I can't see any BIOS entries relating to the A20 gate, so I haven't been able to experiment with that... The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Thanks in advance. -- Matthew Gregan[EMAIL PROTECTED]
RE: Problems installing Debian on a 486
other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... [snip] The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Could it be that the kernel on the rescue disk was compiled for 586+? Could that be causing it? I'm grasping I know, but... :) alan, out on a limb. --- Alan Bailward [EMAIL PROTECTED] http://www.northco.net/alan He who is known as an early riser need not get up until noon.
RE: Problems installing Debian on a 486
At 15:03 1999-03-23 -0800, Alan Bailward wrote: other machine, it brings up the boot: prompt, and then starts to load the root FS from root.bin.. After loading for a while it fails with the message A20 gate not responding!... [snip] The problem machine is a 486DX33 with 8MB of RAM, if you need more info about the hardware, please let me know. Could it be that the kernel on the rescue disk was compiled for 586+? Could that be causing it? I'm grasping I know, but... :) These are the rescue disks from the debian-slink disk-i386 dir... I'm pretty sure they're not using a kernel for 586+ architecture... I should also mention that someone suggested I try the tecra rescue disk. I did that, and had no luck... I get the same message, so now I'm really stumped, having read the readme for the tecra disk I would have though that'd fix the problem. Thanks again... -- Matthew Gregan[EMAIL PROTECTED]
