Fujitsu MRN-3556(150) – “Pentium on module” CPU module for notebooks, among Fujitsu’s early modular Pentium solutions 

The Fujitsu MRN-3556(150) is a CPU module belonging to the first generation of “Pentium in module” solutions for portable computers produced by Fujitsu. With this approach, the CPU is not delivered as a single traditional package, but as a module (often ceramic) intended to provide more controlled mechanical and electrical integration in notebooks of the era, under constraints of dissipation, routing, and serviceability.

This family of Fujitsu modules was offered across multiple frequencies, indicatively from 100 MHZ up to 233 MHZ. The MRN-3556(150) variant directly identifies the 150 MHZ speed grade, positioning it in the mid-range between lower-speed versions (100/120) and higher-speed ones (up to 233).

“CPU on module” for notebooks: practical meaning

The module concept for notebooks typically has these operational implications:

• More predictable thermal and mechanical integration: the module concentrates CPU and interfaces on a stable physical base, simplifying heatsink design and mounting.

• Easier replacement/upgrade compared to soldered CPUs or less service-friendly packaging, within platform limits.

• More controlled bus routing and critical signals: the motherboard sees the module as a defined “block” footprint, reducing layout variability.

Historical positioning: early Pentium-class notebook CPUs

In the period when notebooks began to demand desktop-class performance, modules like MRN-3556(150) address two needs:

• Bringing a high-end CPU into compact platforms with power and thermal limits.

• Standardizing assembly and service across different notebook lines by using the same module base with different speed grades.

Available frequencies and positioning of the “(150)” model

The stated overall range for this module family is 100–233 MHZ. In practical terms:

• Lower-speed versions (100/120) are easier to cool and are often associated with conservative thermal designs.

• Mid-range versions such as 150 MHZ balance performance and thermal constraints.

• High-end versions (up to 233) require tighter platform and cooling design.

Sketch of the most important connections

                 system bus + notebook controller (chipset, memory, I/O)
        ┌──────────────────────────────────────────────────────────┐
        │        notebook motherboard / system controller           │
        │   RAM, BIOS/ROM, I/O, DMA/interrupt, timing, power        │
        └───────────────────────────────┬──────────────────────────┘
                                        │
                                        ▼
                           ┌─────────────────────────────┐
                           │    Fujitsu MRN-3556(150)     │
                           │     notebook CPU module      │
                           │     150 MHZ speed grade      │
                           └─────────────┬───────────────┘
                                         │
                                         ├────────► memory (RAM/ROM via chipset)
                                         └────────► I/O (video, storage, network, etc.)

Table 1 – Identification data and specifications

Table 2 – Operational and design considerations