IBM AT 5170

The IBM AT also known as the IBM 5170 is IBM’s follow up to the IBM PC and IBM XT (and XT-286) home computer. Released in 1984 the 5170 featured a 286 processor and the then new 16-bit ISA expansion slots which would continue to be seen on computer motherboards all the way until the early 2000’s. The AT also supported high density floppy drives, came standard with a hard drive, featured a battery to store system settings as opposed to motherboard switches and was a great machine for then then new EGA graphics standard.

For the duration of this article please take not I will be using the terms 5170 and AT interchangeably to refer to this PC.

The IBM 5170 has a pretty utilitarian look in my opinion but there are many fans of the industrial look of this very sturdy case. My case was rescued from a garage and has some significant rust and scratching but it still fully functional. On the far left we have the standard IBM model badge as well as a lock and LEDs for power and hard drive activity.

On the right side of the case are dual 5 1/4 drive bays. These bays are usually populated by two 1.2MB 5 1/4 inch floppy drives though it’s fairly common to see at least one bay housing a 3 1/2 inch floppy drive via a bay adaptor. All 5170’s support 720KB floppy drives but later revisions like mine also support 1.44MB 3 1/2 drives. I did upgrade one of my 1.2MB floppy drives to a 1.44MB drive but keep in mind you will need a bay adaptor as well as a molex to floppy power adaptor.

Below these duals bays there is also a smaller bay obscured by the front panel that could possibly mount a smaller half height form factor hard drive.

Like the earlier IBM computers the AT power switch is a large red flip switch located towards the rear of the case and on the side.

Looking at the rear we see the power supply on the left side. The AT came with a PSU of about 200w which was sufficient to power a hard drive and several expansion cards and drives. The only built in port on the AT is the AT keyboard port located next to the expansion slots. The AT like the XT supports the now standard eight expansion ports which meant now you had to sacrifice less when picking and choosing expansion cards as the earlier PC only have five expansion slots.

After the five rear screws securing the case cover are removed we can take off the top and have a look inside the AT.

As seen in the image above my original configuration included three expansion cards such as the hard drive controller as well as a serial/parallel port card and lastly a cirrus logic VGA card. The VGA card will be replaced later for something more period correct for the 5170.

Below is a view of the motherboard with the expansion cards removed.

The hard drive is housed in a bay next to the dual 5 1/4 bays. The 5170 shipped stock with an unreliable 20MB MFM hard drive though at some point my AT was upgraded to a 40MB model.

The 5170 lacks any switch blocks on the motherboard and setup is accomplished via a setup program run from a floppy disk. There is an official IBM setup program but it can be a little outdated and the setup program itself may not have options for things such as 1.44MB floppy drives even though the motherboard may be fully capable. A good alternative is a program called GSETUP which you can use with the IBM 5170 as well as other computers which require setup programs.

1 ) CPU – Early versions of the IBM 5170 used a 6MHz 80286 for it’s CPU but later revisions like the one I have pictured were upgraded to an 8MHz 80286.

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Even at 8MHz the AT’s 286 processor is on the slow side as far as 286 CPU’s go. It’s certainly faster then an 8088, even at 10MHz but it’s still to slow to be optimal for many VGA titles that are more action oriented like combat flight simulators. The earlier IBM XT-286 was said to run faster with the same speed CPU due to 0 wait states though I have never personally tested this.

2 ) FPU – The 5170 motherboard does have a socket for adding a 287 math co-processor to assist in more complicated mathematical processing.

The FPU is useful for CAD type programs but it’s usefulness in games is quite limited with only a scarce few games of the time taking advantage of the processors capabilities.

3 ) RAM – All IBM AT’s came standard with 512KB of memory on the motherboard. The 5170 supports up to 16MB of memory though expanding to a full 640KB and beyond does require a memory expansion card.

4 ) Battery – The 5170 motherboard does not have any CMOS battery on the board to save settings nor switches (besides for monitor selection) thus a working battery is essential to save the settings set with the previously mentioned setup programs. The 5170 in order to save settings uses an external battery.

As original batteries are long dead for the most part buying a newer replacement will most likely be required. There are many options on eBay that use AA batteries though usually the wiring is keyed differently. Modification will most likely be required as most of these battery holders are not wired for the AT.

There is a switch between the power connector and the external battery connector. This switch is for selecting the monitor in use. The rear position is for using an MDA monitor and the forward position is for CGA. The position has no effect when using an EGA or VGA video card.

5 ) AT Power Connector

6 ) PC Speaker – The 5170 has a fairly decent PC speaker located at the front of the case.

Let’s take a look at the expansion cards I have installed in my IBM 5170 making it a late 1980’s configuration.

We will start with the two cards my PC had preinstalled and not counting the VGA card I initially installed for testing.

Hard drive controller

I believe this WD based 16-bit MFM controller card which came with my 5170 is the stock card provided for the later revision 8MHz AT’s.

The other card that came with my 5170 was a simple serial/parallel port card which is extremely useful seeing as there are no built in I/O ports.

And now to take a look at the expansion cards I decided to add.

Joystick Card

I decided to add a gameport card since my soundcard of choice did not have a gameport on it as many later sound cards do.

The card I went with was an 8-bit CH Gamecard III automatic. I didn’t have any specific reasons for choosing this card other then it’s what I had on hand although it is nice that it supports two gamepads.

RAM Expansion

Having memory over 640KB isn’t to important on an IBM AT since most games that will run acceptably on this PC only require 640KB or less of conventional memory. Unfortunately the 5170 only came with 512KB of memory stock so although that is enough to play a number of games you really want to get a full 640KB to get the best experience with the AT.

For memory expansion I installed an Intel Above Board which has a total capacity of 2MB but also allows you to backfill the conventional memory to the full 640KB bringing the total memory of the 5170 to 640KB of conventional memory and the difference allocated to being XMS or EMS memory though usually XMS is favored for 286 class PCs. Larger memory cards are available and you can even install multiple cards up to 16MB but I’ve found little use for more then 2MB in a PC of this vintage and class.

Audio

Sound cards weren’t really a thing until 1987 and most games that will run on the 5170 well won’t necessarily require anything beyond PC speaker though a sound card does expand your options. Since I decided to go more period correct with this PC I decided an original Adlib was the best choice.

The original Ablib as seen above from 1987 uses a 1/4 inch audio jack and a simple volume knob. This card uses off the shelf parts but its YM3812 FM chip is widely supported in games. These cards are quite the collectors item these days so I can’t recommend tracking one down unless you want a strict period correct machine from the later 1980’s and have large sums of cash to burn. Almost all later sound cards like the Sound Blaster 16 have perfect Adlib compatibility so I would suggest more people go down that route. There are also a number of Adlib reproductions available for a much cheaper price if you want to keep that original Adlib look. Later Adlib cards from 1990 also switched to a more commonly used 3.5mm audio jack.

Video

In the late 80’s most 5170’s would likely have been fitted with an MDA or CGA video card though the more expensive and fancier option was the official IBM EGA card allowing 16 colors on screen at once.

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There are later smaller and cheaper EGA cards with all the memory built in but the official IBM card just felt right for this PC. The IBM EGA video card only comes with 64K of video memory on the card severely limiting resolutions and colors on screen and causing some games to display an incorrect image. There is a memory expansion daughterboard as seen above which brings the card up to a full 256K of video ram. These daughterboards used to be quite rare though I believe there are third party replacements available. I unfortunately only have a CGA monitor on hand but thankfully the card can be made to display to a CGA color monitor via switches on the card and will display EGA graphics but at a lower resolution.

You can add an ISA VGA video card which would be significantly cheaper and allow the use of much more common VGA monitors if so desired though I find this much less interesting.

Overall the IBM 5170 is a capable PC for the 80’s although I do feel its CPU is a bit on the weak side even at 8MHz speeds. It’s to fast for very early PC games that require an 8088 CPU but for more demanding games of the 80’s a 12MHz or 16MHz 286 or a 386 would serve you much better. I went with a very IBM, period correct build for this article but nothing is stopping you from adding a decent VGA card and Sound Blaster 16 giving a significant boost to this PCs power and expanding the playable game library, though as I mentioned the CPU will still be a bottleneck for more demanding VGA games. In my opinion one is better off with a clone system which are usually smaller, lighter and have more things built in such as more memory and I/O ports. You also most likely do not have to worry about the tiresome setup programs required on the 5170 when using an IBM compatible which is a plus. If you are an IBM fan though this PC can be a lot of fun. The design is seen as beautiful by many IBM enthusiasts the AT is more expandable and versatile then the IBM PC and XT and the case itself is built like a tank.

Anatomy of a 286 DOS PC

Continuing with my “anatomy of” series we’re going to take another step back today and jump back one more generation from my previous “anatomy of a 386” article and take a look at the often overlooked 286 based PC and examine what I feel is pretty close to the “ultimate 286” setup.

The 286 was first introduced in 1982 and was widely used in the mid to late 1980s and even into the early 90s. They came in speeds ranging from 4mhz to 25mhz with 20mhz and 25mhz chips being fairly uncommon. For a CPU that existed in such a transitional time for DOS computers it really doesn’t seem to get a lot of love from retro PC enthusiasts and retro PC gamers. I do have a few ideas of why this may be the case though. The first reason I believe has to do with game compatibility and CPU speed. The 286 simply doesn’t fall into a position where many speed sensitive games demand it. For instance there are a number of very early CGA games that demand a 4.77mhz 8088 CPU to run at the intended speed and even on the slowest 286 will simply run too fast. On the other end there are a few games such as Wing Commander and Bubble Ghost that really need a mid range 386 class CPU and on a standard mid range 286 will run a little too slow. I have run into a few instances where a 286 “felt right” speed wise such as Ultima III with the EGA/MIDI patch but these instances seem few and far between. Many later games also need a 386 to run for non speed related reasons so while a 386 will pretty much play everything one may play on a 286 the reverse is not true. I’m guessing most enthusiasts think “why limit myself” and for the most part their right.

The second reason I believe the 286 is passed over is that finding hardware for a 386 is just so much easier and it will still run most games that run on a 286 plus later VGA games just fine. I wouldn’t call the 286 rare but in all my thrifting and buying old PCs as far as x86 machines go I probably see the 286 the least. Even less than early CPU setups like the 8088 and 8086. The hardware is also a bit less user friendly than a 386 setup which could also be a contributing factor.

Now that doesn’t mean the 286 doesn’t have its place or is useless for retro PC gaming. It makes a fun project and it’s nice to sort of see the transition going on from the 8088 to more modern style boards such as with the introduction of 30 pin RAM on motherboards as well as the common ability to address more than 640KB on the board and things like 16 bit ISA slots which appeared on 286 boards. The 286 is also perfect for playing most EGA games and demanding CGA games that may chug a little on a bog standard 8088. a more powerful 286 such as the 16mhz and up with 4MB of RAM are also very capable of playing VGA titles from the late ’80s and early ’90s and you may be surprised how well it can play them especially provided there isn’t a lot of movement going on screen, point and click adventure games run well most of the time. the common 286-16 as well as the uncommon and border line rare 20mhz and 25mhz 286 CPUs generally outperformed early 386SX CPUs.

and now without further delay here’s my 286.

To be perfectly honest I didn’t have to do much to this machine when I acquired it besides adding some bells and whistles such as a VGA card and sound card. The case is that classic beige tower from the late 80s with the large power switch as opposed to a button as well as extra large buttons for reset and turbo options and a nice green LED speed display. The turbo button slows the speed down to 10mhz though this is still too fast for some early speed sensitive games. The floppy drives I have installed are both high density drives and are a 1.44mb 3 1/2 floppy and a 1.2mb 5 1/4 inch floppy drive. In the case of a 286 I feel the 1.2MB drive is a little more important than in other machines since many games were released in that disk format during the 286 era. Obviously, many of those games were also released on 1.44MB floppy and later CD but if your collecting and playing games from this era you’ll find that many picked up randomly “in the wild” will come on 5 1/4 disk. A CD drive is also very useful for a 286 since as stated earlier many games were re-released on CD format thus having a CD drive makes things much more convenient. It is not though a necessity and you can certainly get by on a 286 without one. I’m using a slow and early x4 drive but later ones should work just fine.

Those eagled eyed readers may also notice the faux 3 1/2 floppy panel below the real disk drive. These weren’t uncommon back in the day. I’m not sure what the point of them was though except maybe to fool your buddies into thinking you had a slightly more impressive setup.

Here’s the back of my 286. As you can see it’s pretty much the same as a 386 and 486 would commonly look. A generous number of slots for possible expansions and an AT keyboard port as well as a standard AT power supply.

Here is a rather jumbled image of the machine with the cover removed and all the expansion cards installed.

A) Hard drive – I went with a 2GB 50 pin SCSI hard drive for this machine. They are a little less common than IDE drives but SCSI lets me make larger partitions, is a little faster in theory and takes a tiny bit of load off of the CPU which helps at these lower speeds.

B) SCSI controller – I went with a 16-bit ISA Adaptec controller for the SCSI. This card is a pretty simple Adaptec AHA-1540. My card lacks a floppy controller but simply sports a 50-pin internal connector and an external connector. I didn’t have any issues with this card and it detected my hard drive first try.

Operating System – I have MS-DOS 5.0 installed on my system. 6.22 should work just fine but I wanted to use a little earlier of an OS to be a bit more era accurate and I didn’t want to go all the way back to DOS 3 or use the generally disliked DOS 4.

Here we have the motherboard with the expansion cards removed.

Motherboard – The board I’m using is an Ilon USA, Inc M-209. This is a rather late 286 motherboard so it supports quite a few features and CPU speeds earlier boards in general do not.

1) CPU – The most common of the 286 CPUs were the mid to mid-high range 12mhz and 16mhz 286s. These are the two most commonly used and all and all are not bad performers. I actually wanted a 16mhz 286 when I considered this project but as fate had it I ended up finding a great deal on my 20mhz 286 system that I couldn’t pass up. The CPU I’m currently using is made by Harris who also produced the 25mhz 286 which was the fastest 286 produced. The Harris 20mhz and 25mhz CPUs were fairly rare and are sought after today by those that do want to forge ahead and build a high end 286. I strongly suspect my 286 board with its 20mhz Harris CPU could outperform a similarly clocked 386SX chip.

2) FPU – Like the 386 the 286 could utilize a separate 287 math coprocessor to speed up the calculation of more complex math calculations. I was lucky that my motherboard came with a FPU rated for the same speed as my CPU at 20mhz. Like on the 386 the FPU chip isn’t really all that much help for games and besides programs like CAD very few games were programmed to utilize the co-pro.

I eventually replaced this FPU with an Intel 287XL which is a cut down 387 FPU made to work in a 287 socket. After running some benchmarks I found the 287XL had noticeably better performance.

3) RAM – RAM on many 286 boards can be interesting as there was a bit of a transition going on and it wasn’t uncommon to find several types of RAM being implemented on 286 boards. This is similar to later 486 motherboards where sometimes sockets for both 30 pin and 72 pin RAM could be found. The 286 itself could address up to 16MB or RAM but I’ve never seen a 286 motherboard supporting more than 4MB onboard. Currently, I have 4MB installed via four 1MB SIPP RAM sticks.

My motherboard supports up to 4MB onboard and can accept either DIP or SIPP RAM. DIP RAM are chips just like the ones used on 8088 boards for memory while SIPP RAM was a short lived style of RAM that used legs as seen below.

4) Nic-cad barrel style CMOS battery and AT power connector.

5) Six 16-bit ISA slots and one 8-bit ISA slot – One of the great things about a 286 motherboard is that 16-bit ISA slots were now standard which opens up a huge variety of options for expansion. Since 16-bit ISA slots continued to be used on motherboards all the way up to the early 2000’s cards are very plentiful and relatively cheap compared to 8-bit ISA cards.

I/O – For my I/O controller I used a simple 16-bit ISA Goldstar controller card. I really like Goldstar cards as they always tend to just work for me. This card supports adding a serial and parallel port as well as two high density floppy drives and two IDE devices such as my CD-ROM drive.

Video – For my video card I went with an ATI VGA Wonder XL24 card. The VGA wonder cards were well-regarded VGA cards throughout the ’80s and very early 90’s. While not as fast overall as cards like the Tseng ET4000 they had a few features which I felt lent themselves more to a 286 class machine. The VGA Wonder XL24 card that I’m using is the last and most powerful Wonder card in the series. Released in 1992 this card is a 8/16 bit VGA card that offers 1MB max of RAM and improvements in speed and bug fixes over earlier cards in the series. The card offers one BUS mouse port which was a type of mouse connector similar to but not compatible with the PS/2 standard as well as two monitor ports. The thing I really like about these cards is that they have both a 15-pin monitor port for VGA as well as a 9-pin port for TTL CGA.  The card also could auto detect the type of monitor connected rather than requiring the use of dip switches to tell the card what it’s displaying. I find this feature very handy for a system like a 286 where you may want to be using a VGA or CGA monitor depending on what you’re playing. Although the VGA wonder XL24 claims to offer 100% CGA compatibility this may not be completely true. Despite this the compatibility with CGA is quite high and having the ability to use a true CGA monitor is always a great option with a 286 where you are likely to be playing a lot of CGA games as well as later EGA and even VGA games. The ability to use both types of monitors and a boast of very high compatibility is definitely a plus.

Sound – Lastly we come to sound. I chose to use the 8-bit sound blaster 2.0 card with the CMS sound compatibility chips installed. The sound blaster 2.0 is fully adlib compatible and offers superior quality compared to the earlier sound blasters. The main draw of this card though was the option to add chips for CMS compatibility or “Creative Music System”. This was an earlier standard used by Creative in their first “Game Blaster” cards and some earlier games use this. The CMS compatibility on the SB2.0 with the added chips isn’t quite 100% but it is close. At one time finding the third PAL chip needed for CMS compatibility was very hard but thankfully someone figured out how to reverse engineer the chip and made it available for most revisions of the SB 2.0 card such as the 049151 revision I am using. If you do have a card with the CMS chips installed remember to remove jumper jp9 as circled in the image below to enable them.

Add the line

SET BLASTER=A220 I7 D1 T3

to your Autoexec.bat file to initialize.

Before I wrap this article up I just wanted to post a few images of another motherboard I have. This one is a later 286-16 board.

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Notice That this board uses standard 30 pin sockets for RAM.

My 286 when I originally acquired it complete with monochrome amber screen monitor.

So what’s my opinion of the 286 and do you need one as a retro PC gamer/enthusiast? The short answer is no. Personally, I enjoy the 286 for its somewhat uniqueness but I can understand why it is usually overlooked. As I stated at the beginning of the article it’s just too fast for the earliest CGA games and as for anything later it can’t really do anything a 386 cant do better. Also compared to a 386 the 286 is harder to find parts for and is generally less capable. If your short on space Id say pass on building a 286 but if you have space, cash and time to spare they can be fun little machines that bridge the small gap between the somewhat archaic 8088 and the somewhat modern feeling 386.