The NEC PC-8401 Reexamined: Part 2

RAM Expansion Cartridges

One of the shortcomings of the NEC PC-8401 is the lack of RAM. By default the computers base 64k is divided in half between file storage and system memory. While 32k is plenty for running the software available in ROM, this limits options when running other software that may require large amounts of memory. Conversely the remaining 32k of RAM dedicated to file storage as a RAM disk places similar constraints on user file and program retention.

Fortunately memory limitations could be alleviated with the addition of RAM expansion cards. These RAM cartridges were to be available in 3 sizes, 128k, 64k and 32k. Rather than adding directly to available application memory, the expansions are used as RAM Disks and must be formatted by the Operating System before use. Once the additional storage is available the PC-8401s base memory may be configured to use the full base 64k as application memory or you may keep existing 32k shared memory split.

No RAM Expansion Attached
32k: Applications RAM
32k: RAM Disk Drive A:

RAM Expanded Machine Option 1
32k: Applications RAM
32k: RAM Disk Drive A:
32/64/128k: RAM Disk Drive B:

RAM Expanded Machine Option 2
64k: Applications RAM
32/64/128k: RAM Disk Drive A:

The PC-8406A 32k RAM Cartridge

The PC-8406A 32k cartridge internals are relatively compact, containing 74 Series logic chips and 16 D446G-15 NEC 2K X 8-BIT SRAM chips mounted on both sides of the circuit board. The SRAM contents are maintained by a CR2032 lithium battery; during battery changes the carts can be powered externally via a 5v barrel jack. Interestingly for the time, just about all the chips contained on the PCB are SMD variants.

The PC-8406A 32k RAM Cartridge.

Unfortunately the PC-8406A 32k pack is on the smaller side of useful, and probably best as a temporary storage device for moving files around. It's not a serious contender as a mass storage device. Even by the file and program sizes of the 1980s it's small. You could for example install MS BASIC on the drive, but then you have very little storage space left for saving programs.

Underside of the PC-8406A 32k RAM Cartridge.

Niggling issues with the NEC PC-8401s overall design choices only increase from there, being that other mass storage devices available of the computer such as the PC-8431A Micro Floppy Disk Unit make no provision for using the RAM carts at the same time, and even the CRT adaptor precludes the usage of the RAM cart as the PC-8401's expansion port provides no means of connecting multiple add-ons.

Effectively there is no easy method of copying the contents of the RAM cart to less volatile floppy disk media. The limitations of the 32k cart apply to a lesser extent to the 64k and 128k expansions, however due to how the PC-8041's memory management works the higher rated cards are inherently more useful as storage mechanisms to begin with.

Severe limitations and all, the RAM carts do help turn the base unit into a more practical computer. Even the 32k cart certainly enhances the PC-8401 user experience, especially in its predicted role as a word processing and spreadsheet powerhouse.

See all entries for this project:  Part 1, Part 2

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The NEC PC-8401 Reexamined: Part 1

A few years back I came across an NEC PC-8401 and proceeded to write up a number of articles during a Retro Challenge month on the machine. Going by blog statistics since RC2017 ended, the NEC PC-8401 is just about as popular in 2019 as it was in 1984. Which is to say not at all. A sad state of affairs then, unlikely to be remedied by further posts concerning this laptop-esque computer. Still, no harm in trying is there?

NEC PC-8401 with PC-8431A, PC-8441A & PC-8406A Expansions

A quick re-acquaintance With the PC-8401

For those who haven't read previous articles on the subject; the PC-8401 series of computers was one of NEC's attempts at introducing portable computing to the business masses. It's main focus is productivity applications, with Wordstar-To-Go, Calc-To-Go, Filer (card filing program) and telecommunications software built into ROM all spring boarding off a CP/M 2.2 OS core.

On the hardware front the 8401 comes with a Z80A CPU, 64k battery backed static RAM (this is shared between RAM and RAM Disk), a rather splendid mechanical Alps keyboard and a just reasonable 80 column x 16 line reflective LCD display panel. Additionally some versions came with a built in 300 Baud modem (sadly not much use today).

When at home or in the office, the machine is powered externally via a suitable 5v to 9v power brick. But what good is a laptop if you can't use it at the pub? Four C Cell batteries answer this pressing need, providing portable power while additionally retaining computer settings and program memory.

Not Quite the Standalone Computing Powerhouse

There are 2 major issues with the PC-8401 as a standalone laptop computer. Firstly and most importantly is the lack of physical memory. While the computer has 64k, 32k is devoted to file storage. This is just enough to keep some documents and spreadsheets stored on the device, but severally restricts what ever else you might like to store on the computer.

Secondly, the screen is problematic, it is usable sure, but it isn't great by any stretch of the imagination. The contrast is poor, and compared to the LCD panel clarity of something like the Tandy model 100 it is not up to the task as a main display for extended periods of time.

It's the Peripherals that Make the PC-8401

It  is the bewildering array of peripherals that lift the PC-8401 onto another level. Memory expansion modules, disk drive adapters and CRT monitor modules turn the basic unit into a fully functional C/PM workhorse. Turning the humble PC-8401 into just the kind of computer you'd want if determined to look oh so very serious about your office computing in 1985.

Perhaps the most valuable peripherals are the Disk adapter, CRT/disk adapter and memory expansions unlock the 32k constraints on storage. The base memory can be configured to use the full 64k, with all storage being taken care of by 3.5" DD disks or the memory expansion modules.

OK so Why the Renewed Interest?

Up until now I've not had more than the base unit to play with, and unfortunately even that started to suffer from some LCD problems with the conductive backing peeling of the panel. Luckily, over the past few months I've managed to secure a number of the much vaunted peripherals and a mostly working LCD panel.

So with a (mostly) working LCD panel in place, we can begin exploring the following over the next couple of blog entries:

• PC-8406A 32k RAM Cartridge
• PC-8441A CRT/Disk Adapter
• PC-8431A Micro Floppy Disk Unit

I can confirm that the PC-8441A and PC-8406A are working just fine, however the PC-8431A is yet to be tested as it's a USA version with the wrong power supply for Australia. Not a huge obstacle, although it has delayed testing.

NEC PC-8401 with working PC-8441A CRT/Disk Adapter

In Part 2 we'll begin getting to grips with the expansion units and some of the issues I have with them. This all promises to be quite interesting, hopefully serving to bring this unique CP/M laptop somewhat out of obscurity.

See all entries for this project:  Part 1, Part 2

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