n-ram-a

This was often the second board added to a NASCOM-1 system – after the buffer board.

As you can see, it had spaces for 16 small RAM ICs so the following capacities could be achieved:

8 off 4k x 1 ICs type 4027 4k bytes
or 16 off 4k x 1 ICs type 4027 8k bytes
or 8 off 16k x 1 ICs type 4116 16k bytes
or 16 off 16k x 1 ICs type 4116 32k bytes

The 4 larger IC positions were designed to accept type 2708 1k x 1 EEPROMs giving a maximum capacity of 4kb of permanent memory.

These figures seem tiny by today’s standards, but remember that the maximum addressable memory for a Z80 (and most other 8-bit microprocessors)is/was 64kb so just two of these boards would completely fill the address space with RAM.

(Just a technical bit…) Using the wire links shown at the top right of the picture the start points of each of the three memory blocks (2 RAM and 1 EPROM) could be positioned at any 4k address within the address space.

Of course, NASCOM owners being who they were, many of these boards were modified in one form or another. Some of the more common “upgrades” were:

Modifying the EPROM sockets to accept 2k or 4k EPROMs.

Modifying an EPROM socket to accept the 8k BASIC ROM.

Modifying the RAM sockets to accept 32k x 1 or 64k x 1 ICs.

There were also mandatory changes to be made in some cases! This board sometimes had a tendency to contract “memory plague” – a rather nasty condition resulting in occasional memory loss. I don’t think anyone ever conclusively proved how this happened, but the cures were many and varied. These ranged from lots of additional components to simply adding wire to the power connections on the PCB. Personally, I have never had these problems on either of my two examples of this board. Maybe I’m just lucky…

Because of all the above modifications, it is quite unusual to find a specimen of this board which is still in its original “as-built” condition.

In the early days of the NASCOM-2 there was a severe shortage of the 4118 1k x 1 static RAM IC which was used as workspace and video memory on that machine. NASCOM had intended that the NASCOM-2 would be sold with all 8 sockets filled with these, giving a computer with 8k user RAM on a single board. However, due to the shortage, many machines were sold with only the two essential 4118 ICs supplied and a free 16k RAM (A) board. This was a mixed blessing. The user was getting 8k of free RAM, but with the inconvenience of the additional board. It did, however, from NASCOM’s point of view, get rid of a few RAM (A) boards! I doubt if it was good for their finances though.

 


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