Upgrading & Tweaking the Toshiba T6400 Laptop

It’s been a while since my last post – I had been really busy with work and other things in my life, but recently have found some time to get back into retro tinkering.

The T6400 still sits on my desk and is one of two Toshiba laptops that I use often (the other being my Toshiba Satelite 4005 CDT). The T6400 has a special place in my collection as it’s the one of the fastest 486 portables in my collection (currently running an AMD 5×86 133 Mhz) and it somehow has hardware contrary to what is listed in it’s specifications, most importantly, that it has 512KB of video RAM. This allows the running of 256 colors (despite the built-in plasma only offering 16 shades of grey). This unique combination means that I can get games that require 256 colors under windows 95 to run on the internal gas plasma screen and not throw up error messages. It also doesn’t hurt that it has 36 MB of RAM from the two memory cards installed.

The Gas Plasma Display & Video Chipset

Both the T6400 and the Toshiba T6400C use a Western Digital / Paradise chipset – specifically, the PVGA1F (WD90C23). There are several interesting things about the T6400’s graphics capabilities:

The T6400 and the T6400c use the same screen connector, (and I suspect, actually identical motherboards) and the screens are interchangeable between the two different models.
The T6400c actually has 512K of video memory, not the 256k as described in literature from Toshiba and I am pretty sure the T6400 also has an identical amount of video memory. This has some interesting consequences for the built in gas plasma screen.
The internal gas plasma display panel can only display 16 colors (shades of grey / orange), and maxes out at a resolution of 640 x 480. However, because the amount of VRAM that the video chipset has, it is capable of displaying 256 colors at 640×480 resolution.
The T6400 / T6400c (along with the T4400 and other similar laptops that are designed to run a greyscale LCD or gas plasma display), have a built in color grey scale controller gate array. This chip along with other chips in the video chipset ‘converts’ color values to 16 shades of grey to be displayed on the internal display, while the external video can display 256 colors (at 640 by 480).
Since the graphics card has 512k of video memory, the computer is capable of using VESA drivers (like univbe) to run DOS and Windows software that require 256 color modes.
Interestingly, this means that the T6400 with a 16 color / shade gas plasma display functions properly in 256 color modes. Software (including Windows 95) will run in 256 color depth, and the colors to be displayed are remapped by the hardware into the closest matching 16 shades of grey.
As far as I am aware, this means that the T6400 is the only gas plasma laptop / portable that (without any hardware modifications) natively runs games and software needing a VESA driver – this means you can run a whole bunch of early to mid 90’s DOS and Windows 95 games that normally would require 256 color displays to run. The onboard color to ‘grey’ scale converter will translate 256 colour output into one of the 16 shades of ‘grey’ on the plasma display. Check out my screenshots below! The color-to-greyscale mapping hardware typically does a very good job at remapping the normal colour pallete used by the software into the 16 shades of grey / orange used by the gas plasma display. How cool is that?!
Note that the T4400SX / T4400SXP (the only T4400 variant that is offered with a gas plasma display) has almost identical hardware to the T6400 (aside from the ISA slots) but with one main difference. The T4400SX only has 256KB of video memory, meaning that it is not VESA compatible, and is limited to a color depth of 16 colors in Windows 95 (unless you use scitech’s display doctor version 6, but the display will be garbled as there is not enough video memory (300KB minimum) for 256 colors. Full write up on the T4400 series coming soon.

CPU Upgrade

Upgrading the CPU is fairly easy – it’s ZIF socket 486, so most 486 CPU’s can be dropped in with ease. However, the socket voltage is 5V, meaning if you want to use later 486’s you will need drop-in upgrades that have an on-board voltage regulator. Additionally, due to the limited height clearance, only QFP style 486 upgrade CPUs will fit. Others that have a large heat-sink, or that use a ceramic 486 with a traditional interposer and voltage regulator board will be too thick and the cover won’t fit. To be on the safe side, I also added a thin copper sheet to the cover of the CPU to act as a makeshift heatsink, for the AMD 5×86 which hopefully allows for increased heat dissipation. This seems to work just fine, but be careful as bare copper can conduct electricity and create shorts if you are not careful.

The performance boost that comes from the drop-in CPU upgrade is substantial, however, the system is still held back by it’s built-in graphics chipset, and unfortunately there is no way to upgrade this as it’s on the system board and is used to drive the gas plasma screen. Oh, and for those with keen eyes, you will notice a removable CPU clock crystal daughterboard- don’t try and overclock this computer – I tried with a plethora of crystals (over 10), with resulting clock speeds from 33 Mhz up to 80 Mhz – none of them worked except the 33 Mhz one that came with the computer. Further research indicates that the onboard controller gate array chip (used in the T4400 as well) can only operate at 16, 25 or 33 Mhz, so 33 Mhz is the only way to go.

Memory

The Toshiba T6400 accepts two ‘credit card’ style RAM cards. These were manufactured in various capacities (2MB, 4MB, 8MB and 16MB), by different manufacturers (Kingston, Toshiba and perhaps others). The T6400 can operate with two 16 MB RAM cards installed for a total of 36MB (4MB onboard, plus 16MBx2), allowing the T6400 to run memory intensive applications, and Windows 95 is quite snappy and responsive. Here’s my first test with 28MB (24 on card plus 4 on the system board).

Expansion Slots

The Toshiba T6400 comes with one built in ISA expansion slot that can fit any full length ISA card. To maximise expandability, I chose to install a dual slot Vadem ISA to PCMCIA adapter, which allows me to use two PCMCIA cards simultaneously. Since the hard drive is limited to specific models and the largest is 200MB (unless you choose to use dynamic drive overlay software and go the CF / SD adapter route), and I am running Windows 95, I have a 1 GB compact flash card permanently inserted into slot 1 (the lower slot) and then in the other slot I can choose between my Panasonic CDROM / Sound Card combo or my PCMCIA network adapter.

The setup above works flawlessly in Windows 95, drivers were automatically installed for the PCMCIA slot. However, there are some quirks when using the seemingly rare dual PCMCIA adapter with the Vadem chipset in dos. For one, if you are using a PCMCIA to CF Card, it seems to only work in the lower slot (my guess this is slot 1). Inserting the card above into slot two doesn’t seem to work, no matter what settings I tried, which is a bit annoying.

Additionally, it was also quite the chore to get both the PCMCIA CD-ROM driver and the PCMCIA CF Card drivers working simultaneously in dos. If anyone out there is trying to get PCMCIA working in dos, here is the configuration that I used for here’s the software I used and my config.sys and autoexec.bat files, along with the CardWiz and CDROM files needed. In the ZIP are the individual files and the folders needed, just add this to a DOS 6.22 or Win 95 setup.

Download CardWiz, Config.sys, Autoexec.bat and CDrom Drivers for my T6400 Setup.

Floppy Drive

If you have a retro Toshiba laptop of an early to mid 90’s vintage, you might have noticed that the floppy drive does not work – many of these computers come with a Matsushita branded slim-line internal floppy drive. These unfortunately are rubber belt driven, and as time does it’s thing the rubber belts essentially disintegrate and turn into a sticky gooey mess. I was fortunate enough to have a working drive when I obtained my T6400, so I was able to install all the drivers for the PCMCIA adapter and other software before the floppy failed. I’m currently waiting for my replacement belts to arrive, hopefully they are a right fit as apparently these drives variants are commonly used across the Toshiba lineup and they are very particular about the belt size and thickness as noted here.

EDIT: the replacement belts that I ordered above worked, but I had to mix and match parts of 3 different drives to get it working reliably. These drives are somehow very sensitive to the belt’s dimensions. A belt that is too thick or thin may not properly stay looped onto the motor and disk drive. Slight differences in belt length (diameter) will affect the rotational speed of the drive. After tinkering with it however, it’s been working fine (reading, writing, formatting disks) for the last 6 months with no problem and the belt seems firmly in place.

The Result

Well – having upgraded my Toshiba T6400 with gas-plasma display to the specs below let’s see how far we can push it:

36 MB of RAM
AMD 5×86 running at 133 Mhz (with improvised copper sheet heat sink to dissipate the extra heat)
200 MB HDD – I kept this stock as the drive seems ultra reliable and you just can’t replace those hard drive sounds 😉 – additionally, the T6400 BIOS will only accept a very limited range of hard drive models made by Conner.
ISA to PCMCIA adapter with:
- CDROM & Sound Card Combo (limited sound through a Panasonic external KXL-D745 SCSI PCMCIA combo CDROM & ISS sound card, music only in dos, some sounds in Windows).
- A ‘permanent’ 2GB CF card, used to store working game & software files & backups – I only use this card to hold games, programs and backups to help ensure it does not get corrupted. The OS’s (Dos & Windows 95 are on the HDD (C:), so if I want to copy software to the T6400 I use a scratch / other CF card to copy software to the actual hard disk, then I copy the software from that onto the ‘permanent’ CF card.

What games can we get to run, and how playable are they (considering game speed and graphics legibility)? Again most of these games require 256 color modes to run, and have their 256 color palletes converted to 16 shades of grey. On top of that the screen is not 16 shades of grey, but 16 shades of not so distinct orange, so the playability / legibility of graphics is obviously not going to be as good as it would be in real 256 colors. However it is quite a novelty to see these mid-to-late 90’s games running on hardware that is really not supposed to be supported.

Windows 95

Grand Theft Auto (1997)

The original GTA does works in 8 bit color mode – as I am using the Panasonic PCMCIA sound card / CD-ROM combo, I can’t get FM Synth in dos and some windows games. However the radio / music does work just fine. The game is a bit laggy as one would expect on this hardware, but it surprisingly it runs well enough to be just about playable.

Command & Conquer RED ALERT (1996)

Red Alert runs surprisingly well, even the pre-game videos and animation play at an acceptable frame rate.

Civilization II

This is perhaps my favourite strategy game, and I think my favourite game overall from the 90s. I spent hours and hours playing this game as a kid. Not only is it highly addictive and well designed, every game plays out differently so the replay-ability factor is 10 out of 10. Despite the 256 color pallete used in the original game being quite colorful (as in almost all 256 colors are used), the remapping hardware does a great job at translating the 256 colors into 16 shades of grey.

However, most laptops / luggables with a gas plasma display are only equipped with 256K (or less) of video ram, and the remapping done by Windows 95 under 16 color mode uses alot of dithering and makes the game almost totally illegible and unplayable. Being that this is my favourite game, I have created a special set of graphics and palette files that optimises the remapping of the 256 colors used by Civilization II into more a more legible 16 shades greyscale / shades of grey / orange. I created this by editing the files in a Win 95 version of Paint Shop Pro. You can chose to run Civ 2 on a T6400 with a 16 shade gas-plasma display in 256 color mode, which remaps the pallette without dithering, or you can switch to 16 color mode and use my custom palette (more legible flag colors, better terrain visibility etc., than the default 256 to 16 shade remapping.)

Note, this palette is needed to run the game with on the Toshiba T4400SX without dithered graphics, as the T4400 can only support 16 shades of grey, with 256 color palettes being dithered to being unplayable. You can download the 16 shade gas plasma optimised palette and associated updated graphics files for Civ 2 here.