Compaq Presario 633 Notes

These are some various links and notes I have collected from working on the Compaq Presario 633. Some of this may apply to other Compaq slimline 486s as well.

Specs

Compaq Presario 633 QuickSpecs: Contains specifications and part numbers. (http://www.elhvb.com/mobokive/Archive/Compaq/Presario/Presario%206xx/Presario%20633/633quickspecs.html)

633 vs. 633 CDS

As far as I can tell, these two systems are exactly the same with two exceptions.

The 633CDS includes a Sound Blaster 16 (CT1770). The regular 633 had no sound card included.
The 633 included a 5.25" floppy drive. The 633 CDS replaces this with a CD-ROM drive attached to the SCSI controller on the Sound Blaster.
The DSP version on the CT1770 on my system is 4.12, this means it exhibits the hanging note bug.

BIOS

Press F10 when the cursor is blinking on the upper right of the screen to enter the BIOS.
The BIOS on my machine is dated 4/14/94. It does not have the 504 MB disk size barrier that is common with 386s and 486s. I am using a 4 GB compact flash card and IDE adpater with no problems.

Jumpers

There is a nice sticker on the right side of the chassis that shows all the motherboard jumper settings. Here is a picture in case yours is missing or marked up.

Video

The integrated video chip is a E4000/W32i. This is good because it is one of the faster video chips from the time.
Windows 3.1 Drivers - Windows 3.1 Drivers for TSENG ET4000/W32/W32i/W32p dated 12/8/1994. These work fine. I had to install by running SETUP from the DOS inside the C:\WINDOWS directory. The SETUP program within Windows could not find the drivers and kept prompting me to insert the disk.
VESA TSR for DOS - The official DOS VESA driver is called TLIVESA.COM. I've read that UNIVBE works as well, but haven't tried it.
The VGA port is one of the annoying old ones that only has 14 pins. You cannot plug a VGA cable into it that has all 15 pins. Either use a 14 pin cable or break off the extra one.

Memory

4 MB of RAM is built into the motherboard.
It has four slots for 72-pin FPM SIMMs. Must be 50-70ns with parity.
The slot closest to the built in RAM will only accept a 4 MB stick. The others will take up to 16 MB. Maximum RAM is 56 MB (4 + 4 + 16 + 16 + 16 MB).

CPU

The motherboard does not have L2 cache and there are no slots to add it.
There is no overdrive socket. The processor has to be replaced to upgrade. (ODPR Overdrive models instead of ODP.)
The jumper selection sticker on the chassis documents settings for i486 25,33,50, and 66 SX, DX, and DX2 processors. I was able to install a 486 DX4 overdrive (DX4ODPR100) with no problem using the settings for a 33/66 DX processor.