Pre-ThinkPad IBM Portables

IBM PS/2 Note N33 SX & N51 SX

Machine Types 8533 / 8551 · 1991–92 · 5 sections

Two early IBM notebooks sold under the PS/2 name: the N33 SX (machine type 8533) is an AT-bus design from IBM Japan, while the N51 SX and N51 SLC (machine type 8551) use Micro Channel. Only the product overview, short notes on each model and the N51 system-board diagrams are transcribed here. The N51's service procedures are in IBM's Hardware Maintenance Manual Volume 1, linked below; the library has no service manual for the N33 SX.

This is a transcribed historical service reference and may contain incomplete captures. Consult the linked original manuals as the authoritative sources before servicing.

Service Reference

Product Overview #

Four variants side by side, compiled from a hardware survey and IBM's product records. A value spanning several columns applies to each of those variants; a dash means no source records it.

Specifications by variant
Specification	PS/2 Note N33 SX (12 MHz)	PS/2 Note N33 SX (16 MHz)	PS/2 Note N51 SLC	PS/2 Note N51 SX
Released	June 1991	February 1992	March 1992
Processor	Intel 386SX, 12 MHz (soldered QFP package)	Intel 386SX, 16 MHz (soldered QFP package)	IBM 386SLC, 16 MHz	Intel 386SX, 16 MHz
Chipset	Western Digital WD76C10		—
Bus	AT bus		Micro Channel
Memory	Standard 2 MB soldered; maximum 6 MB; 1 × 72-pin SIMM slot		Standard 2 MB; maximum 10 MB; SIMM
Storage	2.5" IDE: 40 MB	2.5" IDE: 40 or 80 MB	2.5" ESDI: 80 MB	2.5" ESDI: 40 MB
Display	9.5" passive matrix greyscale (16 shades), 640 × 480
Graphics	Western Digital WD90C20		256 KB video memory	—
Audio	PC speaker
Main battery	NiCad		NiCad or NiMH
CMOS battery	Lithium CMOS battery (barrel) NiCad reserve battery (stick)	—	Proprietary lithium CMOS battery NiCad reserve battery
Power connector	Barrel jack	—
Media drives	External 3.5" 1.44 MB floppy drive (included)		3.5" 1.44 MB floppy drive
PC Card slots	None
Networking	None		Modem (optional)
Ports	Parallel Serial PS/2 Expansion bus port	Parallel Serial VGA out PS/2 Expansion connector	Parallel Serial VGA out PS/2 Micro Channel expansion bus port
BIOS	IBM BIOS
Pointing device	None

PS/2 Note N33 SX #

The PS/2 Model N33 SX, also sold as the PS/2 Note N33 SX, was the first notebook-sized computer IBM released outside Japan. IBM Japan developed it from its own notebooks, fitting a Western keyboard and an external diskette drive. It uses the AT bus and has 2 MB of memory (6 MB maximum), a 9.5-inch VGA (640 × 480) screen showing 16 shades of grey, a 40 MB or 80 MB hard disk, and serial, parallel and expansion ports, and weighs 5.5 lb (2.5 kg) with its battery.

IBM announced it twice: the 12 MHz model 8533-A13 in June 1991, then the 16 MHz models 8533-A33 (40 MB) and 8533-A35 (80 MB) in February 1992, which added an external VGA port.

External Resources & References

Ardent Tool of Capitalism: PS/2 Model N33 SX (Type 8533) — IBM's announcement letters, original system reference disks, deep-dive repairs, component pinouts, logic board layouts and tech specs.

PS/2 Note N51 SX #

The PS/2 Note N51 SX (PS/2 Model N51 SX) and N51 SLC are Micro Channel notebooks. Both run at 16 MHz, the SX on an Intel 386SX and the SLC on IBM's 386SLC, with 2 MB of memory (10 MB maximum), VGA, a 3.5-inch diskette drive and a 2.5-inch hard disk of 40 MB (SX) or 80 MB (SLC).

IBM's service procedures for both models are in the Hardware Maintenance Manual Volume 1, under Model N51 (8551).

N51 System Board (Top View) #

LCD Interface Connector
System-Expansion Port (120-pin)
Keyboard-Control Card Connector
Battery Presence Switch
LCD Interface Connector
LCD Interface Connector

N51 System Board (Bottom View) #

I/O Panel Connector
Voltage Converter Connector
System Expansion Port (120-pin)
Password-Override Connector
Memory-Module Kit Connector
Hard-Disk Drive Connector
Voltage Converter Connector
Hard-Disk Drive Connector
Diskette-Drive Connector
Diskette-Drive Connector
I/O Panel Connector
I/O Panel Connector