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Preface
This document contains not only a partial history of the PC/XT, but is also a good reference for new-comers who are interested in restoring, upgrading, or maintaining their IBM PC/XT. This article has been written in black and green as a tribute to the IBM 5151 Monochrome Display commonly sold with the PC/XT. As a warning, if your eyes are unable to bear the colour scheme selected for this article, you may be in for some serious eye strain when dealing with an actual slow phosphor display. |
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Introduction
In March 1983, the PC/XT 5160 was the second "Personal Computer" introduced by IBM following the release of the original PC 5150 in 1981, and preceding the PC/AT in 1984 and the PC/XT 5162 model 286 in 1985. Together These four machines helped to create industry standards used by computer community. Of these machines the PC/XT 5160 proved to be the most popular due to its improved expansion capabilities over the PC 5150. The early model IBM PCs are undoubtedly the most reliable machines designed in recent computer history, and the IBM PC/XT 5160 is no exception. It was not uncommon for these machines to operate for over a decade without experiencing the slightest problem. Common XT deaths typically involved hard drive or power supply failures, but luckily these components were fairly easy to replace. Getting replacement parts in the 21st Century is becoming a problem as the supply is nearing it's end, however searching the internet can still yield parts. A typical XT weighs approximately twenty to thirty pounds depending on its configuration. These machines are construted from industrial strength steel and plastic, and a common expression used among Vintage PC ethnusiasts is that it is "built like a tank". Not to be taken too literally, this is the kind of machine you can drop down the stairs and still expect to operate. It is unfortunate that IBM no longer uses the high quality components they once did. That quality was lost somewhat during the dark days of the PS/2 when IBM attempted to corner the market. Sadly even more quality has been sacrificed in recent days as competitors in the PC industry set out to drive down costs, creating what is known as "the disposable PC". |
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Opening & Cleaning your XT
Considering the PC/XT was discontinued in late 1986, your system probably will not be in the best condition, although some manage to get lucky and find an old lady who has had one in her closet that she had only used twice. To be on the safe side, it is not a good idea to fire up your XT as a first step, particularly if it has been gathering dust for an extended period of time. In this situation it is highly recommended that the machine be completely dismantled and cleaned before operation. Dust normally tends to concentrate in the power supply, and on or under the motherboard. Unfortunately these are the last two places in your machine where you want dust buildup. To avoid shorting electrical components, use "canned air" or a vacuum to remove the dust. Be careful not to suck up anything important! A complete cleaning of the power supply will probably require opening, but requires a special star shaped screwdriver, which is very hard to find. If you cannot open your power supply, try to suck out as much of the dust as possible. To remove the cover, unscrew the five large screws on the rear of the machine, and side the cover forward. Be sure to keep an eye on your screws. If you lose them you will have a very hard time finding replacements. These are not the screws you will find in modern day computers, and they are also different from the smaller screws holding many other components into your XTs casing. If you are lucky, the former owner has already had the honour of losing some of the screws for you. Pictured below are five casing screws compared to I/O component screws, and "modern" screws. Next, remove all components from the base unit. Start with component cards. Be careful not to damage any of the ribbon cables that might be attached, you may need them again later. Remove all screws holding the motherboard in place. The speaker connector, and the power cables will also require removal before the motherboard may be dislodged. You should now be able to remove the motherboard by siding it away from the power supply. Removing floppy drive(s) can sometimes be a challenge. You may have to first take out the PC internal speaker which is blocking access to one of the screws, which are located on the left side of the drive cage with respect to the front of the unit. If you have a late model XT with half height floppy drives there may also be some additional mounting equipment to remove. In this case, there may also be a screw holding the drive(s) in from the bottom of the case. Make note of how the mounting brackets are installed before you remove them, reassembly may be harder than it seems. The screws to remove the hard drive(s) (if present) are located on the opposite side of the drive cage. Remember to disconnect the power and ribbon cables before tearing the drives out of their bays. The final component to remove is the power supply unit. The screws holding it on are on the back of the casing. Removing the screws on the top of the power supply will cause the fan to fall inside, so unless you have the special screwdriver to open the power supply, you may find it a bit tricky to get the fan back to its original position. In other words, don't play with the fan unless you have the ability to open the power supply.
For a thourough cleaning of your motherboard and component cards you can flatten the heads of some Qtips with a pair of pliers so that they can reach in between the many memory chips scattered across the circuit boards. It will probably take a lot of time and Qtips to finish the job. Remember to remove any cotton that gets lodged in electrical components. This is the best method the author has been able to come up with for cleaning circuit boards. If you have a better one, leave you input in the IBM PC/XT & AT Webforum. After you have fully cleaned and reassembled the inside of your XT, power it up to see if everything is working okay. If the POST does not report any errors and boots up to DOS or BASIC then you're good to go. If you encounter any problems or need some help, try the IBM PC/XT & AT Webforum. As an optional step you can clean the case cover. Take the cover into a work area, and scrub it with a soapy cloth. This should remove most of the dirty spots, and make permanent scratches less noticeable. For stains and sticky spots that won't come off, try spraying them with some WD40 and scrub vigorously. Remember to use soap afterwards to remove the oil. Do not use SOS pads or any other scrub pad that may damage the paint or metal. It is not recommend that you use any chemicals for cleaning, because they often damage the paint and plastic. On the front of your over you will find a small silver IBM logo. If it looks beaten up, you can remove the damaged plastic membrane to restore its shine. If it is in good condition leave the membrane alone to preserve its originality. If your plastic panel has yellowed you are out of luck.You will either have to paint it or find a new cover. IBM machines usually do not yellow since they are made from superior plastics. |
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The PC/XT System Board During the four year production run of the PC/XT two versions of the system board were released. The original 64k-256k boards introduced in 1983, and updated 256k-640k boards from 1986. It is possible two determine the board type by looking near the ISA slot furthest from the CPU. The memory capacity will either be silkscreened on the board, or on a small white tag. The tags are more commonly found on 256k-640k boards. Both the 1983 and 1986 design are based on the same circuit board. The only noticable differences being the 64k-256k version lacks a ROM that goes into U84, and a jumper that needs to be soldered to activate the ROM. Modification of an older board allows you to install the full 640k memory. The instructions to upgrade a 256k board to 640k are available in the "hardware information" section of our webpage. Unfortunately the upgrade method is too complicated for most users. Fortunately there is another method for upgrading memory size. A number of companies designed memory upgrade boards for ISA slots. These memory boards are available in a number of different memory configurations, but you will probably want one that comes with 384k memory so you can run the full 640k (384k+256k=640k). The most popular of the 384k boards were the AST Sixpakplus cards, which also feature a real-time clock powered by a lithium ion battery. Unfortunately these clocks only tell time from 1980 to 1999. Don't worry too much about this problem, as many XTs did not even have clocks. On a clockless machine the year resets to 1980 ever time the machine is started. Software and jumper settings for the SixPakPlus can be found HERE.
Before we get to far into the review, we should probably discuss a bit about the layout of the XT motherboard. The 8-bit XT motherboard consists of (8) 8-bit ISA slots, 4 banks of 16-pin DIP memory (0-3), an 8088 CPU socket, an 8087 math coprocessor socket, and block of DIP switches to configure your XTs components. Remember, your XT does NOT have a CMOS, everything is taken care of through this DIP switch block and DEBUG. The most important thing to remember with your XT board is how to properly install the 16-pin memory DIPs. As always, you want make sure that your memory is plugged in the right way by verifying that the notch on your chip is aligned with the notch on the chip socket. The next thing to remember is that when you are installing the memory, that you do NOT mix and match the memory speeds and densities in the same bank, and to completely fill each bank you are using with all 9 DIPs. Not following these instructions will certainly result in failure. There are also certain densities and speeds that you should not install into your motherboard. DO NOT install chips under 200ns, and make sure that the chips you are installing are either 64kbit or 256kbit. If you do not have a 640k motherboard you will only be able to use 64kbit memory. Installing the 256kbits will work, but they will be detected as 64kbit. It does not really matter which memory banks you have occupied, but it is probably a good idea to start from bank 0 and work your way down to bank 3. I highly recommend that if you currently use 200ns chips and have access to 150ns chips or faster, that you replace them. But remember to keep your old memory chips incase you run into memory failures in the future. Installing the memory alone will not quite complete your memory configuration. To let your XT know how much memory is installed, you will need to set the memory switches on the small blue switch box (shown below) to the appropriate positions. The switch settings can be found HERE. This switch box is also used to configure the number of floppy drives, install a math-co, set video type, and set the post loop test. I have one last word regarding your memory installation. You may have seen some places on the internet with instructions for upgrading your XTs memory capacity beyond 640k. Doing this is a no-no, and can cause problems with your video card. Even though an 8088/8086 can address 1 meg of (1024k) of memory, PCs are limited to 640k conventional memory. You cannot configure the memory as UPPER or EXTENDED either because the 8088/8086 does not support that type of memory.
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PC/XT 5160 VS. PC 5150 You may be wondering what the big difference is between the IBM PC 5150 and IBM PC/XT 5160 is. Well, in terms of overall performance they are pretty much equal, but the XT was given 8 ISA slots over the PCs 5 slots for greater expandability. In the PC/XT You must make sure that you do not use the ISA slot closest to the CPU, because it is reserved for IBM's special asynchronous serial card. Another difference between the two systems is that the XT lacks the 5-pin DIN port for connecting a tape recorder. On the PCs it was located right beside the keyboard port on the back of the unit. I guess that when IBM designed the XT they figured that using tape recorders for BASIC programs were too obsolete to bother with. The most important improvement with the XTs is that they come with a 157 Watt power supply unit (PC uses 63.5 watt) which allows you to connect internal hard drives. PCs casings also lacked mounts for half height hard drives, so in most cases the user had to get a special hard card that plugged into an ISA slot. Just like XT motherboard, power supplies come in many different styles but they all deliver the same 157 watts of power. Below is a picture of the power supply unit that came with my XT 5160-089. Beside it is a power splitter, you may need one these to use three internal drives or two splitters for four internal drives. When you reconnect the 2 power connectors for the motherboard, remember to make sure that the black wires on the sides of each connector are facing one another or your system will not turn on.
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Processor & Math-coprocessor
All IBM PC/XT 5160s come standard with AMD or Intel 8088 CPUs running at 4.77 MHz. These chips are 16-bit internally, and 8 bit externally. The 8088 CPU comes in a 40-pin DIP package. There are many upgrade paths you can take without having to replace your XT motherboard. Upgrading to the 8086 is not one of these options though, because it is not pin compatible with the 8088. The 8086 wouldn't be a worthwhile upgrade anyway, since its only difference is it is 16-bit externally. The NEC V20 is probably the simplest upgrade to perform. Once again it is running at 4.77 MHz in a 40-pin package, but its internal architecture is different, providing up to a 50% performance increase in raw CPU speed. Other upgrade options are 286, 386, and even 486 upgrade cards that plug into an 8-bit ISA slot. To install these you usually have to remove your old 8088 and plug a cable into the CPU socket which runs off the upgrade board. Although they provide a huge increase in processing power, getting memory above 640k that comes on the card to work is often a hassle and requires software from the card manufacturer. I don't recommend replacing the CPU at all, because it destroys the XT's originality. As mentioned earlier in this review you can also purchase a 40-pin 8087 CPU to run along with your 8088. You will probably not notice any difference in your XTs processing speed, but if you run math intensive software, the 8087 is definitely worth while. The 8087 I use is made by Intel, and relabeled by IBM. It is really strange, because I have never seen an 8087 that runs at 6 MHz before. It will not matter what the speed it, because the math-co will run synchronous to your 8088 CPU. My 8087 also has a weird gold plate on the top of it, but I personally like the plain ceramic models better.
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Side Note
If you want to find the date your XT was manufactured, you can find it on a cloth tag which is attached to the PC internal speaker. If your speaker has been damaged, don't panic. You can easily find a replacement at a nearby Radio Shack. The speakers that come with your XT are among the best in PC internal speakers. The speakers you find in modern day casings are often very small, and very quiet. These suckers produce loud clean beeps, and are perfect for all of those great EGA and CGA games you have lying around. In the picture directly to your left, you might notice some plastic braces next to the PC internal speaker. If you are planning on installing long cards, it is probably a good idea to make sure they are in place to keep your cards from wobbling around. |
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Video Display Adapters
With the release of the PC/XT, there were only two video options offered from IBM. Basic configurations came with an MDPA (Monochrome Display Parallel Adapter) which was a text only monochrome card. As the name indicates, these cards included a built-in parallel port, which would save you the trouble of having to spend more money to buy a parallel port adapter. The CGA card (Color Graphics Adapter) was the more expensive adapter offered from IBM. CGA wasn't an impressive graphics system, even in its day. Its two main graphical modes were 4 colour 320x200, and two colour mode at a "medium" resolution of 640x200. CGA also offered a 16 colour mode at 160x100, but due to its extreme blockiness, it is seldom use. Despite the limitations of the CGA system, many titles were written for it. In 1984 IBM released the EGA card (enhanced graphics adapter) with the introduction of the AT. EGA gained tremendous support in the gaming world, and was also practical for some graphical business applications. Unlike CGA, EGA offered 16 colors in all graphical modes, including a new 640x350 high resolution mode. EGA also introduced the concept of palletized graphics. EGA selected its 16 colors palette of 64. The IBM EGA adapter is highly recommended for use in the PC/XT, as it is the best consumer level It may be more convenient for you to get an EGA card from another manufacturer though, because finding an original IBM can be difficult. Getting one with the 256k daughterboard is even more of a challenge. Almost all the clone manufacturers offered their cards with the full 256k video DRAM. To the right is an IBM MDA card, and to the left is an ATI VGAWONDER which does an excellent job at EGA with its 9-pin EGA port.
For those of you who must absolutely have better graphics, there is on last option for you. IBM released the VGA (Video Graphics Array) card in 1987 for the use with their PS/2 machines. The VGA board offered 256 colour in 320x200, and 640x480 high-res mode with 16 colors. Like EGA, VGA is also a paletted display. In 256 colour modes, colours are selected from a palette of approximately 256,000. IBM VGA boards were only available for microchannel PS/2 machines, but other manufacturers quickly released 8 bit and 16 bit ISA versions for use with the older machines. Although having a VGA card in your XT is nice, most programs that use it and that can run on your XT are very slow. On top of this, you will not be able to use a true IBM vintage monitor with your XT. In theory you can use an SVGA adapter (Super Video Graphics Array), but it would be so slow that it would not be worth the trouble installing. SVGA offers 256 colors in modes 640x480 and beyond. Here is an overview of the display adapter types discussed: MDPA (MDA): 4k RAM, monochrome, 80 column text CGA: 16k-64k RAM. Resolutions: 40 and 80 column text
modes in 16 colour EGA: 64k-256k RAM. Resolutions: All CGA resolutions supported VGA: 256k RAM. Resolutions: All CGA and EGA resolutions
supported SVGA: 512+ RAM. Resolutions: CGA, EGA, and VGA resolutions
supported Although these cards were the most popular, an XT owner had a few other choices as well. The most popular alternatives were MCGA, PGA, and Hercules. MCGA (Multi Color Graphics Adapter) wasn't that bad of a card. It offered 256 colors in the 320x200 graphics resolution, but unlike the VGA adapter, it did not offer high resolutions with decent color depths. Because of this, and the fact that MCGA was not well supported, it did not gain much popularity. The same goes for the PGA (Professional Graphics Adapter) card in terms of popularity. I don't really know much about the PGA other than that it was designed for CAD/CAM programs. The PGA did poorly because it required 3 ISA sockets, had terrible support, and was EXTREMELY expensive. The Last alternative mentioned was the Hercules adapter made by a company called ...Hercules. This was the only alternative card that really went anywhere. Although this card offered high resolution graphics, they were only in one color (or monochrome). This card was meant for users with monochrome monitors of course. Because this card was not multi-color, it was fairly cheap, which is the reason why it was able to gain some popularity. |
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Selecting a Proper Display Adapter for your Monitor
When you choose your display adapter, it is very important to make sure that you get a monitor that will be compatible. There are several bad combinations of video cards and monitors that you should stay away from. If you are going to use any type of card which has a 9-pin connector, you must make sure that you have a monitor with a 9-pin cable. There is one exception to this rule however. With a special adapter you can hook a 15-pin VGA monitor up to a 9-pin EGA/CGA/MDA video adapter. DO NOT get adapters that work the opposite way though. Trying to use a 15-pin VGA card with a 9 pin EGA/CGA/MDA monitor will NOT WORK because of the difference in frequencies. You should also make sure that you do NOT use an EGA card with a CGA monitor. The monitor may display the lower resolution EGA modes correctly but the higher resolutions will probably not work correctly. MDA monitors will work perfectly with both CGA and EGA video cards. The three types of monitors that IBM offers for your XT are the IBM 5151 MDA (monochrome green), the IBM 5153 CGA (low-res 16 color), and the IBM 5154(right) EGA (hi-res 16 color). If you are not sure which one you have, check the tab on the back. The IBM 5151(left) is the most reliable of the 3 of these monitors. You do not have to use a monitor from IBM, but they are nice to have.
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Floppy controllers/drives/IO ports
Generally there is not much choice available when selecting a floppy controller. Almost all users stick with the standard floppy controller from IBM, which supports 360k 5.25" floppy drives. Most of them support 720k 3.5" drives as well, however it is rumored that some of the older ones do not. There are also rumors that the 320k/160k/180k drives are also supported, but since I have not been able to get my hands on any of them, it is hard to say if that is accurate. If you are smart you will stay away from the 320k/160k/180k drives, because they are junky and unpopular. The drive that I highly recommend is the IBM 360k 5.25" full height drive. The reason for this is that they are the easiest to replace, and are very reliable. But if you have the mounting hardware required for a half height drive then by all means use it. I find that the IBM 360k full height drive made by Magnetic Peripherals are much more reliable than the drives made by Tandon. The Tandon drives have small orange-brown connectors on the back end, while the drives made by Magnetic Peripherals (bottom right) have red or blue clear plastic connectors. I have found this from my experiences, but it is up to you to decide which one you use. I went through three Tandons(bottom left) in two months.
What about 1.2/1.44 MB drives you say? The IBM controller does not support these formats, but if you are lucky you can find a newer one made by a 3rd party manufacturer that does. Just make sure that you get one that is easy to configure and has a manual. The standard IBM controller does offer one advantage over the newer controllers...it has a massive 40-pin port on the back which allows you to hook up 2 external floppy drives. So if you REALLY want to, you can have a total of 4 floppy drives hooked up to one machine. Since this feature usually isn't all that useful, you are probably going to want to use something better if you are working at usefulness rather than originality. I have found that the best card to install is a newer 16-bit multi I/O card that supports 8-bit operation mode. The reason for this is that most multi I/O cards contain 4 I/O ports on them ...usually the printer and COM1 (serial) port on the card, and a game port and a COM 2 (serial) port on an extender cable. This can free up 2 ISA slots since everything is integrated onto one card. The downside to this is that you cannot use the IDE port because the card does not have onboard BIOS, so it will probably be a good idea to disable it. The card I use in my XT is a Winbond ISA multi I/O pictured bottom left. Remember, if you go with the IBM controller, you may need to track down some I/O cards if your memory or video card does not have them.
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Hard drives and controllers
When XTs were first released many people could not afford to buy hard drives, and instead went with dual floppy drives. But if you had the cash to spare you originally had the option of buying an XT equipped with a 10 MB MFM full height drive. At the time this would have been considered an outrageous amount of disk space. But, a few years later when parts were cheaper and programs were larger, IBM made 20 and 40 MB MFM half height drives available with their units. All systems that had hard drives also required controllers so that you could attach your drive to the computer. Unfortunately when IBM first started shipping these drives and controllers, they didn't think that people might one day wish to upgrade to larger hard drives, so if you bought a system with a 10 MB MFM hard drive, that controller was only good for a 10 MB MFM drive and below. At least IBM had the common sense to design the newer controllers with backwards support for newer drives. All hard disk controllers allow a user to attach up to 2 hard drives. MFM/RLL controllers require two cables to hook up to a drive. A command cable and a smaller data cable. If you want to add a second hard drive, you need to make sure that your hard drive command cable has 2 ports on it. Make sure that you do not confuse it a dual floppy drive cable, because they are the same size, but do not work. On a command cable the first drive connects to the port closest to the controller. Each of the drives will require its own data cable. And remember that when you install these cables that the red line on the cable is aligned with pin 1 on the controller, and pointed towards the power connector on the hard drive end. When installing two drives, you must also make sure that their jumpers are set correctly. The best hard drive controllers to use are made by Western Digital. What makes them good is that they are small, and support 40+ Meg hard drives. The WD1002A-27X is for RLL, and the WD1002A-WX1 is the MFM model. To the right is my WD1002-WX1.
Although most XTs came with MFM drives you could install
drives of other formats such as RLL, IDE, ESDI, and SCSI. RLL drives are identical
to MFM drive, but they use a much better method of storing data on the disk. They
also require RLL controllers. Make sure you do not mix RLL and MFM drives and
controllers, because it is possible to damage your hard drive(s). To format an
MFM or RLL drive you need to get a system disk with the following files: FDISK,
DEBUG, FORMAT, and SYS. When you boot to the disk you must first run the program
DEBUG. To get into the low level formatting program, you need to call the BIOS
on the hard drive controller. The most common command is G=C800:5. If this does
not work, you need to find the correct command for your manufacturer. Once in
the program, it will ask you a few questions about your drive. If you do not know
the information on your drive, then you are going to have to get it from the drive
manufacturer. The next step is to run FDISK. In this program you select the type
and number of partitions that you would like to make. After you make the partitions,
you will need to format them again using FORMAT. Finally to make your partition
bootable you need to run the program SYS. Installing the other 3 types of drives
mentioned above uses the same basic installation method. If you wish to run IDE,
ESDI or SCSI, you need to make sure you find an 8-bit controller with an onboard
BIOS, otherwise it will not work. These cards also have their own DEBUG codes,
so you will need to find them.
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Input Devices
The most high quality keyboards that are loved by all (almost all) were made by IBM. When you buy a keyboard from IBM, you can expect it to last you for a good 12 years. IBM at first only offered one keyboard when you purchased an XT ...which is known as the IBM 83-key. Its main noticeable differences from today's keyboards are that they only have function keys 1-10 which are located to the far left of the keyboard, and that it lacks the lock LEDs. Despite these disadvantages they are incredibly well built...and very heavy. It is made from a thick industrial plastic, and all keys make a confirming clunk when pressed. They are also somewhat easy to repair when they break. ALL parts are removable so if you have transplant parts your keyboard could last you forever. IBM also started offering a 101 keyboard in 1986. Although it is still high quality it just isn't the same as the 83-key. If you see a 101, be sure to pick it up because they can be very hard to come by. Remember, when you are using any type of 101 key keyboards, you may need to put it into XT compatible mode by playing around with the switches on the bottom. Some people may also want to use a mouse for word processing etc. This is one of the only things that IBM isn't very good at. Their mice are clunky and uncomfortable. The best serial mice are probably made by Microsoft and Logitech, because they are supported in almost all DOS programs with mouse support. The best mouse driver to use with them is the one that comes with DOS. Depending on which one you have, the driver will be called either MOUSE.COM or MOUSE.EXE. To make your mouse look official, you might want to try to get your hands on a nice IBM mouse pad.
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Sound cards
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Final Notes
Always remember to take care when assembling and disassembling your IBM PC/XT. Try to avoid NOT bumping, scratching or defacing your unit with stickers or pen. Always park your hard drive(s) before relocating your machine, and keep spare screws, and other parts handy incase you run into problems in the future. If you are not going to be using your XT for extended periods of time, try to cover it with a sheet to prevent dust from getting inside it, and close the latch on the floppy drive(s) to ensure they remain dirt free. It would also be a good idea to turn your machine on every couple of months to ensure that the heads on your harddrives do not seize up. This article may be due to change in the future. Any recommendations and contributions are appreciated. Please report any mistakes in the "Website Development" section of our IBM PC/XT & AT Forum. |
Article written by: P. Holowaty
Edited By: S. Pearce
Moved and updated By: Matt
Many updates By: John Harshbarger
Re-edited by: P. Holowaty
Creative labs sound blaster 1991
Pro AudioSpectrum