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Version 3.00C
PC-186 Memory Upgrade

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 :

Bank 0
Bank 1
Bank 2
Total
128K
128K
128K
128K
256K
128K
128K
128K
384K
128K
512K
640K
512K
128K
640K
512K
512K
1024K
512K
512K
512K
1536K

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:
RM Nimbus half memory card

Here is a fully populated card:

RM Nimbus memory card

And installed

RM Nimbus memory 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:
RM Nimbus PC-186 Slimline Memory Module

And another version:
RM Nimbus PC-186 Slimline Memory Module

Other manufacturers produced 3rd party add-on memory cards for the Nimbus
Heres one for the Nimbus X10 from Centec:

RM Nimbus PC-186 Slimline Memory Module from Centec
And another version, fully populated to 1Mb
This board has been repaired by the museum to replace the ageing capacitors
RM Nimbus PC-186 Slimline Memory Module from Centec full card
For a tutorial on the memory upgrade please see the below video:

Information on memory upgrades for the Nimbus PC-186
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