Talk:IBM Personal Computer AT

message: The article should note that the AT keyboard is not compatable with the IBM PC or PC/XT or clones thereof, and that many keyboards were produced with an XT/AT or PC/AT switch to work with either until the PC and PC/XT systems began to be phased out of use in the early 1990's. (I saw many lots of PC and PC/XT systems sold at auctions for a few dollars a pallet in 1990~1992.)
: It should be noted that the AT keyboard is incompatable with the PC and PC/XT for these two reasons. 1. Different scan codes. 2. The A20 gate control circuitry is in the keyboard. The A20 gate is used for switching to Protected Mode. An IBM AT (or any clone without a 'fast A20' BIOS setting or setting to boot without a keyboard or to not test the keyboard during POST) will not function at all without a keyboard connected. Later clones moved the A20 control onto the motherboard and had a 'Fast A20' setting in the CMOS setup to use it, then could be booted without a keyboard.
:: The A20 gate control circuitry is NOT in the keyboard. In all models of the IBM AT, it has always been in the 8042 keyboard controller chip, which resides on the motherboard. The purpose of the A20 gate is to emulate the PC's 8088 when the 80286 CPU is in real mode (that is, emulate the PC's wrapping of addresses at the 1 MB mark). The IBM 5170 can't boot without a keyboard because it presents "301-Keyboard Error (RESUME = F1 KEY)" on screen and because there is no keyboard, the F1 key can't be pressed to resume to boot sequence. 'Fast A20' is functionality found on certain clone ATs that disables/enables the A20 line faster than what the keyboard controller chip can do it. 'Fast A20' can cause problems which is why most BIOS allow users to turn the functionality off. Sphere808 (talk) 04:27, 26 December 2010 (UTC)
thread_title: Keyboard

message: 16 DMA chnnels? I don't understand. I have always thought DMA channels were from 0 to 7. —The preceding unsigned comment was added by 82.155.155.251 (talk • contribs) 19:40, June 30, 2006  (UTC)
:It seems you are correct. The incorrect number in the article was copied from a web site with bad information.  Thanks for the heads up.  --Blainster 00:41, 6 July 2006 (UTC)
thread_title:  DMA channels 

message: Why is this article deleted? This is certainly notable enough for Wikipedia. —The preceding unsigned comment was added by Nick Warren (talk • contribs) 06:27, September 19, 2006  (UTC)
:The article has not been touched in nearly three weeks.  Did someone steal your account to make this edit?--Blainster 22:06, 19 September 2006 (UTC)
replies: text: The page looks fine to me. I recently saw an image page that was redlinked, but had the image there plain to see.  I assume that was a system bug.  Is that what you see here?  --Blainster 21:46, 20 September 2006 (UTC)

text: Maybe the database servers are really slow, but I'm still seeing September 1, 2006 as the last edit.  --Blainster 23:18, 20 September 2006 (UTC)
replies: text: That's right. Re-saves never appear in the history (try it). Mirror Vax 00:04, 21 September 2006 (UTC)
thread_title:  Who deleted this? 

message: Should explain how DOS did not take advantage of most of the 80286 features, so most people with PC AT computers were using the 80286 chip as a fast 8086.  As late as 1991, it was fairly common for even people with 80386 computers to be running DOS with the chip in 8086 emulation mode (this only changed with the wide adoption of Windows 3.1 beginning in 1992). AnonMoos (talk) 09:11, 5 December 2019 (UTC)
replies: text: The 286 processor was designed with a protected mode architecture that required restarting the processor to switch back, which made it unattractive for software developers to use the PM architecture. One piece of software that took advantage of this architecture, but never had to switch back to real mode was IBM Xenix 1.0, another was the EMM driver for DOS.
Deskview, and Topview took advantage of memory addressing of extended memory, by using it as expanded memory. ( extended memory was the 16 bit addressing, and expanded memory was using a window above 640K to swap memory into addresses that could be addressed by real mode ). 
Mot people ran the AT with DOS, because DOS was most popular, and XENIX was $500. There were several other OSs such as THEOS. The 386 chip added a Virtual 8086 mode, but running DOS on a 386 under windows was interesting: If you had a swap file set up, the DOS window would be a Virtual 8086 mode process, but if paging/swapping was turned off, the DOS prompt would be run in Real Mode.  I have not done extensive testing on this, because my interest lies in Xenix. 
I used both Windows 2.0.1, and Windows 386 2.1 on a 386, but never used the VIRT8086 to check the mode the DOS prompt was running in. When the 386 came around, because XENIX for the 386 was $500, I switched to Microport UNIX, and ran dual drives, and never checked out wheather Windows 3.1 ran a DOS prompt in real mode, if paging was turned off, but I assume that it did. Most common was to either run Windows applications in windows, and not use the DOS prompt, or not start windows and run the DOS application. I would say it was uncommon to run DOS prompt in Virutal 8086 mode, and even less common to run a DOS application in Virutal 8086 mode for that reason. I supported many users with 386s.  
The Maximum memory on an IBM AT was 4MB using stock IBM Cards, ( 512K on the mother board, and 7 512K cards ), and using after market adapters you could only get ONE manufacture of card to sit at an address above 4MB, and it would only add 1MB for a maximum of 5.25MB.
Despite the ability of the processor to address up to 16MB - 63k,  142.254.26.9 (talk) 18:29, 26 June 2020 (UTC)
thread_title:  80286 processor underutilized 

message: :The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion. 
The result of the move request was: moved. (closed by non-admin page mover) Vpab15 (talk) 22:00, 16 February 2023 (UTC)
replies: text: IBM Personal Computer/AT →  – I searched for IBM PC AT, IBM PC/AT, IBM Personal Computer AT, and IBM Personal Computer/AT in Google, but with 2 characters at the start (+") and the 2nd character as the last one. This page should be moved per WP:COMMONNAME since it is more common to write without a slash. 176.88.83.247 (talk) 18:52, 8 February 2023 (UTC)
thread_title:  Requested move 8 February 2023