Atari 400 64k Ram Card

[Paul Westphal]

I had a problem with my 400, so I took it apart to reseat the chips and boards and came to find out that it had a 64k ram card in it. It was made by Atari ( CAO61553 ). Are these rare? Print ?(0) shows 37902(48k). And can you use these in a 800 to avoid using all the slots up for ram? ( it would keep it cooler ) Thanks. BTW it works again.

[Rybags]

Maximum contiguous free Ram with Atari Basic enabled/inserted will always be 40K regardless of system.

 

64K upgrades for 400/800 generally have the extra Ram appear at $C000-$CFFF, IIRC $CFFF controls which bank appears (?)

 

The thread by ClausB explains how memory slot assignments work in the 800 http://atariage.com/forums/topic/177885-atari-800-ram-selection/

 

32K module is usually the biggest size for unmodded 800s. But of course there is banking schemes like Axlon (?) on the 800 which allow for bigger module size with bank selection similar to 130XE for the extra Ram.

Edited October 25, 2013 by Rybags

[+Guitarman]

I had a problem with my 400, so I took it apart to reseat the chips and boards and came to find out that it had a 64k ram card in it. It was made by Atari ( CAO61553 ). Are these rare? Print ?(0) shows 37902(48k). And can you use these in a 800 to avoid using all the slots up for ram? ( it would keep it cooler ) Thanks. BTW it works again.

 

Atari made a ram upgrade board for the 400. I'm sure that's what is installed. I have one in one of my 400's. They are specifically for the 400.

[+orpheuswaking]

Correct, all of the Atari branded 48k upgrades for the 400 are in reality a 64k board that can only be addressed at 48k. I recently purchased four of these in Atari packaging as kits and they are all identical. (comes with the board and four precut wires)

[BillC]

Maximum contiguous free Ram with Atari Basic enabled/inserted will always be 40K regardless of system.

 

64K upgrades for 400/800 generally have the extra Ram appear at $C000-$CFFF, IIRC $CFFF controls which bank appears (?)

 

The thread by ClausB explains how memory slot assignments work in the 800 http://atariage.com/forums/topic/177885-atari-800-ram-selection/

 

32K module is usually the biggest size for unmodded 800s. But of course there is banking schemes like Axlon (?) on the 800 which allow for bigger module size with bank selection similar to 130XE for the extra Ram.

The MOSAIC 64K Bank Select RAM card actually allows raising RAMTOP to 52K and using the extra 4K above BASIC. With this RAM card there are actually 4 * 4K switchable banks accessible in the 48 to 52K window.

[+wood_jl]

I remember seeing the 64K on the Atari 400 "official" 48K upgrade too, and getting excited. Was there *ever* an application for that card - or a variation of it - that actually used the 64K? Why did they put an extra unusable 16K on it in those days, when RAM was so expensive?

[Scooter83]

Biggest I've seen so far is ram cram. 32k

[Rybags]

Actually, yes you can employ the RAMTOP alteration and put your graphics in the $C000 window.

 

Of course you're limited to not using the hires modes that otherwise need ~ 8K and you can get into real trouble if the memory requirement of your Basic program approaches where the Display List+Screen would normally reside when RAMTOP points to the 40K boundary.

 

Isn't there mods around to allow utilizing more of the 64K on the Atari boards? I guess chances are they employ dodgy piggybacking and mounting ICs in mid-air.

[tep392]

Why did they put an extra unusable 16K on it in those days, when RAM was so expensive?

They didn't make 48k ram chips. The boards they made back then would have one chip for each bit, so 8 of the 64k x 1bit chips. You could make a 48k board using 8 32k chips plus 8 16k chips, but you would have twice as many memory chips and a more complicated board and address logic. It was cheaper to use the 64k chips and waste the 16k that overlapped the OS and hardware address space. The more sophisticated designs made the 16k available through bank switching.

[+wood_jl]

They didn't make 48k ram chips. The boards they made back then would have one chip for each bit, so 8 of the 64k x 1bit chips. You could make a 48k board using 8 32k chips plus 8 16k chips, but you would have twice as many memory chips and a more complicated board and address logic. It was cheaper to use the 64k chips and waste the 16k that overlapped the OS and hardware address space. The more sophisticated designs made the 16k available through bank switching.

 

Hey, thanks for that explanation!

[BillC]

They didn't make 48k ram chips. The boards they made back then would have one chip for each bit, so 8 of the 64k x 1bit chips. You could make a 48k board using 8 32k chips plus 8 16k chips, but you would have twice as many memory chips and a more complicated board and address logic. It was cheaper to use the 64k chips and waste the 16k that overlapped the OS and hardware address space. The more sophisticated designs made the 16k available through bank switching.

I don't believe the 32K x 1 chips were made either, IIRC density always went up in multiples of 4. So it went from 16K x 1 to 64K x 1 to 256K x 1 to 1024K(1M) x 1 to 4M x 1.

 

This means that a 48KB card using 16K x 1 DRAM would require 24 ICs which use +5V/+12V. Switching to 8 x 4164(64K x 1) ICs, which use only +5V, would reduce power consumption/heat production as well as cost once the price of 4164 ICs dropped.