External battery

Motherboards used to have 3.6V barrel batteries. One good thing about them is that they are rechargeable. They charge themselves every time computer is powered on so in theory they should have never need to be replaced. Unfortunately they are like Duracell batteries, they leak and might work while leaking.

Leaking can damage motherboard so remove leaking batteries immediately. I recommend to remove them before they start to leak. Removing is easy, just cut them with pliers and there will be no need to desolder anything.

Locate the 4-pin external battery header from the motherboard. It should be close to the battery and there should be a jumper to select between internal and external battery. Pin 1 of the header is +, pin 2 is not connected (and usually missing completely so there are only 3 visible pins). Pins 3 and 4 are -. You can use multimeter to locate pins 3 and 4 since they are connected together. This is useful if your motherboard has all 4 pins available and there are no good markings.

Here are what you need to build an external battery: CD-Audio cable, battery holder, 3 AA batteries, soldering iron and some electric tape. It is possible to do this without soldering iron if you use some connectors or just tie the wires together.

You are going to need the type of CD-Audio cable that has one large connector that fits to the external battery header. That is the most common type of CD-Audio cable so it will be easy to find. Battery holders are easy to get as well. You can get those from Chinese ebay sellers and the price is very cheap even with postage. Just make sure you get holder for three AA batteries that are connected in series to get 4.5V.

You might wonder if 4.5V is too high since the barrel battery is 3.6V. I once had a “real” external battery and once it had depleted I opened it. It had 3.7V lithium battery in it. That made me try to build my first own external battery using 3.7V lithium-Ion rechargeable battery. It worked but it self discharged way too soon to be of any use. Using non-rechargeable lithium battery would have been far better but those are expensive.

Modern systems use 3V lithium batteries that are shaped like a coin. I tried those and 3V was enough to hold BIOS settings but it was not enough for RTC to tick properly. I'm told that it will work better on some motherboards.

Then I read from Vintage Computer Forum that 4.5V is not too high. Finally I found one interesting picture from a 386 motherboard. Next to the external battery header there was printed the voltage range and the range was 3.6 to 4.5V. So I finally decided to try 4.5V. So far I've tried it on two motherboards and both without problems. I don't know how long the batteries will last but I'll let you all know when I need to replace them.

Back to the assembly instructions. Here I have CD-Audio cable that has large head on the other end and large + small head on the other. This is good since this cable can be used for CD-Audio even after building the external battery. Alternatively I could have build two external batteries using one CD-Audio cable.

I should have taken first photo before cutting anything but I didn't think of it until it was too late. The pictures should be self explaining. Just be careful when connecting the small CD-Audio head back as the orange wire and thin black wire are connected together. It might be wise to use multimeter to see how the wires are connected before cutting anything. Some CD-Audio cables have different colors and possibly only 3 wires.

If you don't need to keep the CD-Audio cable usable it might be wise to use longer cable for the external battery. This helps to place it in a location where leaking does not do any harm. Finally remember NOT to use Duracell batteries since they will certainly leak eventually.

CD-Audio Cable. The short part with black connector will be used for the external battery.

Wires are now soldered.

 

First tape all individual wires, then tape them all together.

This step is optional. I inserted toothpick to the not connected hole and then broke the toothpick. This makes harder to connect the external battery wrong way. Also note that red wire is used as + wire.

External battery is now completed. The tree AA batteries are connected in series.

My first computer

I'd like to tell something about my first computer. I don't have any pictures from it and I can't remember was is year 1990 or 1991 when I got it (I was 10 or 11 years old then). More likely 1990 because I think I got NES as Christmas present on 1989 (I was hoping for a computer).

My first computer was quite generic XT clone build in AT clone case used by many PC XT/AT clones. Brand of my first computer was Trifunic and it was assembled in Finland.

I remember the specs very well. I learned a lot with and from this computer. Monitor was IBM 5153 CGA display. I can't remember was the keyboard IBM as well but I do remember it was 84-key XT keyboard. Trifunic didn't come with mouse but I got one later.

Other specs were:

• 8 MHz Turbo Board with NEC V20 processor
• 640 kiB RAM
• 100 % compatible CGA clone adapter
• Seagate ST-225 20 MB MFM hard drive
• 720k 3.5” Floppy Drive
• 360k 5.25” Floppy Drive
• Multi I/O card of some sort (it did have serial port to plug the mouse in)

As you might have guessed by now, system like that bought in 1990 must mean it was previously owned and it was. Nobody had slower PC and I couldn't play many of the games my friends did. I always wanted new computer back then but now I'm glad what I got. It made possible for me to start from XT systems and feel the progress of PC hardware and games from the beginning.

Friends dad did some work with computers and through him I got the Trifunic. At their place I saw a PC for the very first time. I don't know it's specs other that it was also XT clone. It had amber display that looked so amazing.

Before I got the Trifunic I was told it had color display, and it did. CGA is able to display 4 colors in graphics modes. We were at my friends place to test the computer for the first time (my friends dad must have installed DOS and some games in it). Digger was the very first game we tried on it and it looked and worked great. King's Quest III was the second game we tried and it appeared black and white! What a disappointment. There was key combination to switch to color mode but that was even more disappointment. King's Quest III looked so much better in amber display, not to mention in real color display.

About the same time my friends dad got 386sx system with VGA. No need to guess where we played all the games after school.

I didn't know back then but Sierra's AGI games support CGA composite output. I'm sure I had one in my Trifunic but even if I had known it, I wouldn’t have anything to plug it in. European PAL televisions back then didn't support NTSC and even if they would have, I had black and white TV for the NES. RGB Output in AGI games were always black and white or 4 color mode with quite awful palette so I used the B&W mode. Later SCI games from Sierra had much better CGA RGB color support.

And those I mostly played on my Trifunic; every Sierra game that run on it. It didn't matter that the copy of KQ3 had disk 2 missing or Larry 3 was corrupted so that it always froze when entering bamboo forest. Or that I only knew one phone number from Larry 2 (3425, can't forget it) so it took a while to get in the game.

Other games I played were Lucasfilms Indy 3 (I'm one of the few who thinks Last Crusade is better game than Fate of Atlantis but Atlantis didn't work on my Trifunic, of course), Monkey Island and Zak McKracken.

Then I really spend many hours on Prince of Persia (one of the best games ever), SimCity and Ducktales. Again it didn't matter how slow they were as long as they supported CGA.

If a game worked slow back then it didn't mean slow frame rate like today. When game was slow, the character was moving slower that it supposed to. In my opinion that is better alternative than slow frame rate (actually the frame rate was slow as well but it feels completely different on 2D games than on 3D games).

I wanted to let you know how my PC gaming started because that certainly affects what I consider to be “best” retro gaming XT system.

XTIDE Universal BIOS beta 3 bugs

What's going on with XTIDEUniversal BIOS? It's been four months since v2.0.0 beta 3 was released.

Beta 3 was supposed to be last and quick beta testing phase before releasing stable v2.0.4. Well, beta 3 turned out to be a lot more buggy than I thought it would. It is buggy but fortunately most of the bugs are quite minor and doesn't effect many users, except that slave drive support is broken.

I believe most people use XTIDE Universal BIOS on their XT systems along with XTIDE or Lo-tech XT-CF boards. Actually I do most of the testing with Pentium system so AT builds get most of my attention. I have 8 MHz Turbo board for testing XT builds but I don't have enough space to keep all my testing equipment available all the time. I also test with my gaming 286 and 486 systems from time to time.

Back to the bugs in beta 3. I started to do lots of testing to get stable version released and I fixed those minor bugs quite soon I found one. I decided to try to install Windows 95 and 98 along the testing process. There were no problems to install Windows 95 but Windows 98 was something else. One bug was exceptionally hard to fix and it took weeks.

Windows 98 install always crashed to blue screen at certain point. I was able to install Windows 98 using motherboard BIOS but again I got the very same blue screen when loading Windows once I had switched back to XTIDE Universal BIOS. Eventually I found out that the blue screen happened when Windows 98 tried to load protected mode floppy driver (HSFLOP.PDR). Renaming it forced Windows to use real mode floppy driver and that helped. Next I had to find out how XTIDE Universal BIOS was incompatible with Windows 98 floppy driver.

If you are familiar with XTIDE Universal BIOS, then you must know that it has a feature to allow install DOS from any floppy drive to any hard drive on the system. DOS itself only supports boot from first floppy or hard drive on the system. Drive number translation, or swapping, is a way around this limitation. During drive detection, you can use hot keys to select what drive(s) are to be set as primary. For example to boot from second hard drive in the system, press D. This sets second drive to be drive C and first drive to be D. Next you can press A to boot from floppy drive containing DOS install disk. Or you can press B to set second floppy drive as primary floppy drive and boot from it. Now you can install DOS from second floppy drive to second hard drive.

Floppy drives are handled by motherboard BIOS and there can be hard disks handled by other BIOSes as well. They don't know anything about drive swapping so XTIDE Universal BIOS must do all the drive number translations. One thing to complicate this is that the other BIOSes can make recursive INT 13h calls (INT 13h contains drive access functions) so XTIDE Universal BIOS must not translate the drive number more than once.

Previously XTIDE Universal BIOS temporarily restored system INT 13h handler before calling it. This way the system BIOS could do as much recursive calls as it needed to. Replacing the INT 13h handler was something Windows didn't expect and that caused blue screen. Now XTIDE Universal BIOS disables drive swapping before it calls system INT 13h.

I still have more testing and fixing do to before stable version can be released. I just don't have as much time for coding as I would like.

I'm a project leader of XTIDE Universal BIOS, a BIOS expansion to use large modern hard drives, CF cards and micro drives on old PC systems starting from original IBM 5150. But this blog is not just about XTIDE Universal BIOS, although I plan to write about it from time to time.

I'm a collector of sort. I don't want to own every piece of PC hardware ever released or fill my home with computers I don't have time to use (well, I don't really have time to use those I already have...). I aim to build “best” possible XT, 286, 386 and 486 systems for retro gaming purposes, or more properly DOS gaming purposes. That is the reason why building Pentium system is not so interesting.

Building perfect retro PC is actually impossible as there are no such thing as best components to build best possible system. There is no such thing as best sound card or even best Sound Blaster. For example my 486 system has three internal sound cards but it is still a compromise solution. And for my 286 I've tested many different VGA adapters but I'm sure there are even betters out there. I'm going to write about those and many other things eventually.

I hope my blog will be useful for other collectors and retro PC gamers such as myself.