The Nimbus PC-186 mainboard memory varied throughout the revisions, however all options
were generally less than the maximum permitted, unless specified as a server .
The Nimbus has 3 banks of memory each of which can be either 16x4164 or 16x41256 giving 128K or 512K per bank.
These banks are as follows :
bank0 on nimbus motherboard.
bank1 first half of expansion card.
bank2 second half of expansion card.
The valid combinations are :
The slimline 'facelift' model could take 1024k onboard and therefore this page generally refers to the original Nimbus PC
An additional memory card could be fitted to go above 512k.
Being an 80186 based platform, these were 16-bit CPUs with 20-bit addressing.
This led to a memory addressable limit of 220 × 1 byte = 1,048,576 bytes or 1 megabyte.
Above 1024k it can only be accessed as a RAMDISK.
Removal of the card should be carried out carefully whilst supporting the mainboard from flexing
Heres a Half Populated Card:
Here is a fully populated card:
An upgrade requires the insertion of 16 x HM50256P-15
(262144-word x 1-bit Dynamic Random Access Memory)
Once Installed, the RM Device driver, RAMDISK.SYS
can now access the additional memory as a silicon disk, in
this case E:
The silicon disk was significantly faster than the currently available floppy
or Winchester drives.
The content, of course, was volatile but had many uses in the server arena, serving applications that were copied over on bootup of the server.
Prior to the upgrade the response was:
The Slimline PC-186 uses a different memory module to take
into account the reduced height:
And another version:
Other manufacturers produced 3rd party add-on memory cards for the Nimbus
Heres one for the Nimbus X10 from Centec:
And another version, fully populated to 1Mb
This board has been repaired by the museum to replace the ageing capacitors
For a tutorial on the memory upgrade please see the below video:
Information on memory upgrades for the Nimbus PC-186