The Resurrection of an 18 year old PC - the 486DX2 66Mhz

After comparing a Pentium 2 to a Pi, I started thinking about that old 486DX2 66Mhz chip on the mantelpiece. It was last in a PC back in 1993 and that was broken down for parts in 1995. I was thinking what if, just what if I could get that thing running again.

The Case: The case was still in one of the rooms, somehow a bird made a nest in it. It was covered in droppings and the case was missing.
Power Supply: The AT 180watt power supply was still in the case with the cables and the pc speaker magnet and ribbon.
Motherboard: The empty motherboard (made by SiS) was still in the case. 6 ISA slots and 2 Vesa Local Bus slots (extended ISA). No PCI slots in sight!
Memory: I had 8 sticks of 1mb simms(30x9) upstairs somewhere (the same ones that were ripped from it in 95). 2 sticks were stolen for a SoundBlaster 32 PnP.
Harddrive: The 240Mb Connor harddrive was no where to be seen. Thats ok, that 4.1Gb drive over there might do the trick. Think it was in a Pentium around '97.
Keyboard: Luckily I still had the keyboard as it uses a dplug connection. There is an old serial mouse with it.
Monitor: The Goldstar 15" monitor is not around anymore so I cheated using an old 15" LCD.
IDE Harddrive and Floppy drive controllers: The PC came with an ISA card. Looked like any soundcard - but what it did was house the IDE connectors & control logic for the hard drive and floppy drive.

Videocard:
The original video card, a Vesa Local Bus ISA video, with 1mb of Vram was in an old plastics Dunnes shopping bag with pins sticking through the plastic... might work says I. The beloved Tseng ET4000... Vesa Local Bus was before PCI or AGP or PCI Express standards came out. But was distinct from 16-bit ISA slots.

Soundcard:
The original one i had was an NX Galaxy Pro, an 8-bit "Soundblaster Compatible" card with ADLIB sound. This emulated SB fine but sometimes the cpu suffered.
A year later got a 16-bit Vibra 16 Soundcard (almost an exact SB clone) with a x3 CDROM reader (the caddy box tray kind). The motherboard has no IDE talking of. So the IDE connector was on the soundcard to connect the CDROM to the motherboard. The IDE controller on the soundcard emulated an matsumi cdrom. Which a Windows 98 boot disk in later years would actually detect. In this case dos drivers were supplied with the cdrom package.

Unfortunately, the soundcard I found was actually a Soundblaster 32 PnP designed for a plug and play bios when didnt really take off until 1996+. So no sound is possible for the moment but the pc speaker should do fine in games or utilities (not recommended).

This was a Reeves PC order from the UK, took a month to arrive and when it - it had to go back for a bios fix - the keyboard randomized keypresses - C would print Z and so on. This was an actual fault on the bios chip not the country region dos drivers.

What I did was:
1. Plugged in the CPU, slipped in the 8 sticks of ram. Put in the Power. Turn it on. 8 beeps. That means the cpu is ALIVE! It's ALIVE!
2. Brought down the LCD, slipped in the Tseng ET4000 vga card. Connected the vga cable. Turn it on. I see a bios flash up! 2 beeps. No Floppy or HDD which is expected.
3. Inserted the IDE controller card. Connected the floppy drive. Solid led light wrong way, flip around the cable still no joy. Tried a different card. Turn on - it finds the floppy drive!
4. Insert ms-dos 6.21 boot disk - it reads the disk upon bootup. No harddrive found obviously but works.
5. Rummage for a loose harddrive somewhere in the house. Ah 10Gb harddrive from 1998 - No Joy. Next a 4.1Gb drive from '97. Might work....
6. Boot up and ms-dos tells me I got a drive installed and would you like to install on it? Heck yes.. go for it! Whirrl Whirrrl...
7. I check the contents of the 4.1Gb drive... C:\Dos 5Mb installed, with config.sys, autobat.exec and command.com. Works.. with 241Mb free. I was expecting this..
8. Reboot fdisk (an old hard disk partition manager) tells me I have a 251 Hard disk installed. Ok......
9. Reboot - enter the Bios - under the hard drive - its entered as type 47 (well options from 1 to 46 gave different sizes). Type 47 is like user defined. You enter the number of Cylinders, Sectors etc and it calculated the drive. But this entry was for the old drive back in 1993. Its not auto detected or sized. So enforces the old size on the new drive.
10. I google the serial online and find the geometrics for the new drive. Now the bios says 4170Mb. Great, now lets format it.
11. Reboot. Fdisk tells me i have... 478Mb total when given a primary partitioned. Then I remember LBA... Large Block Addressing overcame the 501Mb limit.
12. This Pc does not support LBA. That's it a max of 478Mb on this. No Matter, it's still better than 248Mb which it had day one. It now nearly rivals the size of a CDROM disk.
13. Install Dos 6.2.1. It all works. Install Doom, works, Install Fractint for floating point unit work - works fine. Might install windows and see.

The CPU is quite hot and never had the basics of a mere heatsink. I would think it be more stable if it did. It did freeze rarely back then. But to think that I'd get this working after 18 years is amazing. A clock doubled 486DX2 66Mhz on a 33Mhz bus. With DosBox and an archive of 18,000 dos applications and games - might try a few benchmarks on it.

Alternatively perhaps a version of FreeBSD would work on 8Mb ram and install on 400Mb. No network and on an ISA architecture would be hard pressed to find such a card and even then the bandwidth would'nt be able to travel along the ISA bus.

When I was googling for drivers I saw this post on Vogons and my breath was taken away - Someone had done the same in 2010. The screenshots are very good, Board, memory (much clearer to see - the white banks of 8 rows). A smaller version of my ET4000 Tseng videocard, the onboard removable 256K cache on the motherboard. The same type 47 user set on the bios screen for the hard drive he had. He has a SoundBlaster Pro card so he'll have sound with the cdrom able to piggy back to the motherboard bus. The screenshots also show you can indeed install a 386SX or DX with/out a co-processor as well on the motherboard.


In screenshots I did the following:

The PC booting up with floppy and in the process of seeing if the harddrive is dead/alive or recognised. Notice the date on the soldered bios battery. It is still working after that length of time. Although when I turned it on - it was slowly losing track of time - 2000 instead of 2012, but still better than 1993. Set now and its fine.



A simple screen shot of the bootup screen when the floppy, harddisk and dos installed and then rebooted. American MegaTrends Intern (AMI) is the bios dated from 1992. The memory is 8Mb and im sure some of you know about the 640Kb conventional memory barrier where a program had to start and then access the memory beyond 1Mb either as extended or expanded memory (EMM386 was a driver that emulated such memory). Memaker works as does Defrag and Chkdsk from the prompt. It really does feel like a primative version of linux now. The help was there typing: help memmaker or whatever you wanted to read.
But to see the letters 80486DX2 again is just... magic!


There is the 1st bios screen - simply with the user defined entry (47) for the 4.1Gb drive i found - Note the bios calculates the size right but the bios can't allocate more beyond the 501Mb limit (which is LBA large Block Addressing issue - which was extended shortly before Windows 95 came along). It's also FAT16 which means you can only have 65536 files on the system. I did a bare check on the Raspberry Pi to see what a bare minimum install did (and i mean before anything) and it still installed 25k files. My Ubuntu system has 251k files. You could get around that limit partitioning the drives in separate drives with 65k files on each etc. But you still had an issue with slack space (where by a 1k file would still eat a 4k cluster, or a 5k file would eat 2 4k clusters (boxes)) FAT32 expanded this, NTFS gave security and now with ext3, ext4 etc we are spoiled for choice. File naming was limited in max length by: 12345678.123


This is inside the PC case. The long card on the left is the video card (Tseng ET4000 1mb). Notice the slot is longer than shorter slots. Thats is vesa local bus. There are 2 on the system here. The 2nd card is the IDE connectors/controllers allowing the hard drive and floppy to connect and be detected. Sadly there is no soundcard in one of the other slots. The 486DX2 is the chip near the ribbons (its name is upside down here). The pc speaker magnet can be seen botton middle attached to the harddrive case. In the middle you probably can see three sticks of ram (8 there in total), in the middle of those ide grey cables in white long sockets. The empty socket is where a 386 would go.




Finally with the case back on and cleaned (still need the 5.1/4 bay covers). I installed and tested a few items. Doom was always a good dos "application" to stress the cpu and video. Right now the chip is rather hot. 20fps doom - well maybe.. I'll have to benchmark it.