EINTR.net / systems / compaq / presario433

Compaq Presario 433

I don't consider this low-cost, all-in-one computer from Compaq a proper *nix workstation. But I think it deserved this page because of the interesting form factor.

Pictures

Notes

The CPU was upgraded to an Evergreen 586 / AMD 5x86 133MHz.
- The AMD 5x86 is designed as a low voltage CPU. Incompatible with this motherboard.
- The Evergreen packaging makes the Socket 3 CPU backward compatible with the Socket 486/1/2.
- The original CPU was an Intel 486SX 33MHz (Ran NetBSD).
- I upgraded first to an Intel 486DX2 66MHz (To run OpenBSD).
- A 486DX (with FPU) is the minimum requirement to run OpenBSD/i386. OpenBSD doesn't have software floating-points.
Memory was upgraded to the maximum of 20MB from the original 12MB.
It run a slimmed down kernel to save much needed memory. OpenBSD 6.8 doesn't support this low amount of memory anymore in GENERIC kernels. This installation is non-standard and unsupported.
The network card on picture is a we0 but it gave me issues. It has been replaced by a ALN101 (NE2000 compatible, jumperless ISA card).
F10 to access BIOS.
The BIOS does not support ISA-PnP. Which means ISA cards must be set with jumpers or through vendor supplied program. The network card is manually set to IRQ5 in order to support the DOS Packet driver.
The power cord plugs in the back of monitor in such a way that it acts as a simple lock for the motherboard drawer.
The original Compaq floppy disk died. It was replaced.
The hard-drive crashed since. It was replaced with a 120GB IDE 2.5 inch laptop drive in an 2.5 to 3.5 inch adaptor.
The BIOS has limitations for hard disk size. Natively, I wasn't able to go beyond about 1GB recognized. I now use the EZ-Drive int 13h extension boot software to access up to 8GB from DOS. OpenBSD use LBA directly through the controller and can access the whole disk.

Specifications

CPU	133 MHz AMD 5x86 P75 - Evergreen 586 packaging makes it compatible with the 486 PGA Socket
FSB	33 MHz (or 25MHz) (Supports 5V CPU, Socket 486/1 compatible, running at a fixed multiplicator of these 2 speeds)
Memory	20 MB (max 20 MB - 4 MB on board + 2 x (1, 2, 4 or 8 MB FPM 72 pins SIMM 60-70ns)
Bus	16 bits ISA (not PnP) - 2 slots on a riser card
Video	Cirrus Logic CL-GD5420 512K SVGA capable (800x600: 256 colors) built-in 14" monitor with inactivity timeout.
Sound	Standard PC beeper Microsoft Sound System (do not know it's capability) [not supported in OpenBSD]
Disk Controller	1 x ATA controller [generic wdc driver in OpenBSD, standard master/slave capable] internal 40 pin male connector [single hard-disk short cable provided]
Case	All-in-One Computer 1 x 3.5 inch floppy drive 1 x half-height IDE hard-drive
External Connectors	Bottom row, from left to right: PS/2 keyboard - 6 pin mini-DIN female connector PS/2 mouse - 6 pin mini-DIN female connector COM1 serial port - DB9 male connector LPT1 parallel port - DB25 female connector Game port (joystick) - DB15 female connector COM2 internal 2400 baud fax-modem - left: line in, right: handset [factory option]

Boot, dmesg and serial console output

On Screen:

EZ-BIOS: Initializing...
EZ-BIOS: Hold the CTRL key down for Status Screen or to boot from floppy...
EZ-BIOS: Continuing startup...

Loading......
probing: pc0 com0 com1 mem[634K 15M a20=on]
disk: fd0 hd0+
>> OpenBSD/i386 BOOT 3.44
cpaq.EINTR.net
com0 19200 baud
switching console to com0

On Serial Port:

>> OpenBSD/i386 BOOT 3.44

cpaq.EINTR.net 
Sun Oct 19 01:04:47 2025

Region 0: type 1 at 0x0 for 634KB
Region 1: type 1 at 0x100000 for 19456KB
Low ram: 634KB  High ram: 15360KB
Total free memory: 20090KB

boot> 
booting hd0a:bsd: 1881900+209924+143368+0+466944 [125914+107+133072+119340]=0x2f2880
entry point at 0x201000

[ using 379008 bytes of bsd ELF symbol table ]
Copyright (c) 1982, 1986, 1989, 1991, 1993
	The Regents of the University of California.  All rights reserved.
Copyright (c) 1995-2020 OpenBSD. All rights reserved.  https://www.OpenBSD.org

OpenBSD 6.8-stable (CPAQ68) #1: Sat Oct 18 02:18:47 EDT 2025
    root@qemu11.o37.ca:/root/src/kernels/compile/CPAQ68
real mem  = 20504576 (19MB)
avail mem = 16232448 (15MB)
random: good seed from bootblocks
mainbus0 at root
bios0 at mainbus0: date 12/30/93
bios0: ROM list: 0xc0000/0x8000
cpu0 at mainbus0: (uniprocessor)
cpu0: AMD Am5x86 W/T 133/160 ("AuthenticAMD" 486-class), 04-0e-04
cpu0: FPU
isa0 at mainbus0
isadma0 at isa0
fdc0 at isa0 port 0x3f0/6 irq 6 drq 2
com0 at isa0 port 0x3f8/8 irq 4: ns16450, no fifo
com0: console
com1 at isa0 port 0x2f8/8 irq 3: ns16450, no fifo
pckbc0 at isa0 port 0x60/5 irq 1 irq 12
pckbd0 at pckbc0 (kbd slot)
wskbd0 at pckbd0: console keyboard
vga0 at isa0 port 0x3b0/48 iomem 0xa0000/131072
wsdisplay0 at vga0 mux 1: console (80x25, vt100 emulation), using wskbd0
wsdisplay0: screen 1-5 added (80x25, vt100 emulation)
wdc0 at isa0 port 0x1f0/8 irq 14
wd0 at wdc0 channel 0 drive 0: <WDC WD1200BEVE-00A0HT0>
wd0: 16-sector PIO, LBA48, 114473MB, 234441648 sectors
wd0(wdc0:0:0): using BIOS timings
ne2 at isa0 port 0x280/32 irq 5, NE2000 (RTL8019), address 00:60:67:25:b8:b8
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
lpt0 at isa0 port 0x378/4 irq 7
npx0 at isa0 port 0xf0/16: reported by CPUID; using exception 16
root on wd0a (6b51e7e6facba0d5.a) swap on wd0b dump on wd0b
fd0 at fdc0 drive 0: 1.44MB 80 cyl, 2 head, 18 sec
Automatic boot in progress: starting file system checks.
/dev/rwd0a: file system is clean; not checking
/dev/rwd0e: file system is clean; not checking
/dev/rwd0d: file system is clean; not checking
/dev/wd0i: 588 files, 2055136 free (64223 clusters)
/dev/wd0j: 24 files, 2087616 free (65238 clusters)
machdep.kbdreset: 0 -> 1
starting network
reordering libraries: done.
starting early daemons: syslogd ntpd.
starting RPC daemons:.
savecore: no core dump
clearing /tmp
starting pre-securelevel daemons:.
kern.securelevel: 0 -> 1
creating runtime link editor directory cache.
preserving editor files.
starting network daemons: sshd inetd.
starting package daemons: sendmail.
Saved dmesg in /var/log/dmesg.OpenBSD.6.8.cpaq.EINTR.net.CPAQ68.v1
starting local daemons: cron.
Sat Oct 18 21:15:33 EDT 2025

OpenBSD/i386 (cpaq.EINTR.net) (console)

login:

Jumpers Markings

Motherboard:

	P1	1-2	25 MHz
		2-3	33 MHz

	P2	1-2	PQFP	# Soldered CPU only
		2-3	PGA	# Socket 486/1 used

	P3-P4	1-2	ODP/ODPR
		2-3	SX(PGA)

	P5	1-2	ODPR	# 168 pins OverDrive Processor Replacement
		2-3	ODP	# 169 pins OverDrive Processor
		3-4	SX(PGA)

	P6	1-2	CMOS CLEAR


	Original 486SX  33MHz:	P1:2-3	P2:2-3	P3-P4:2-3	P5:3-4	P6:1-2
	Upgraded 486DX2 66MHz:	P1:2-3	P2:2-3	P3-P4:1-2	P5:1-2	P6:1-2

	Evergreen 586 / AMD 5x86 133MHz
		Motherboard:	P1:2-3	P2:2-3	P3-P4:1-2	P5:1-2	P6:1-2
		Evergreen:	WT	4X	NORMAL

Evergreen 586:

	WB	# Write-Back Cache	[Late 486 CPU and motherboard feature]
	WT	# Write-Throught Cache	[Early 486 motherboard]

	4X	# Speed multiplicator for CPU
	3X	

	OVRDRV	# Raise signal to disable the original CPU
	NORMAL