Will an XL/XE work with only 2 32K chips?

[gs80065xe]

I was wondering if you ever needed to replace ram in an 8-bit and didn’t want extra ram, would the Atari work with only 2 32K chips? For example, Remove all 8 chips in a 65XE. Then install only 2 41256-15 chips.

[Tickled_Pink]

No. The reason that the 65XE has 8 chips is because each one provides a bit for each memory address. So if you only put in two chips, of whatever capacity, you'd only get two bits for each memory address.

Edit: And remember that when you're talking about DRAM capacity, you're talking in kbits, not kbytes. So a single 32K chip only stored the equivalent of 4KiloBYTES of RAM. So, even if you were able to get two chips running on it, you'd just have 8Kbytes in total.

Edited April 6, 2020 by Tickled_Pink

[BillC]

5 minutes ago, gs80065xe said:

I was wondering if you ever needed to replace ram in an 8-bit and didn’t want extra ram, would the Atari work with only 2 32K chips? For example, Remove all 8 chips in a 65XE. Then install only 2 41256-15 chips.

The XEGS and later versions of the 800XE were designed like this, they used 2 x 4464/41464(64k x 4bit) chips. There isn't any point modifying a machine using 4164(64k x 1bit) chips like this, it would be a lot of work for no real benefit.

[+Nezgar]

At that point you might just remove all the RAM from the sockets, and stick this 64KB module under your CPU:

https://lotharek.pl/productdetail.php?id=291

 

Or 64KB + 512KB of extended RAM in one board for a 600XL:

https://atariage.com/forums/topic/277204-some-new-not-really-hardware-made-by-tfhh/?do=findComment&comment=4259597

(I wonder if it would fit/work anyway in an 800XL?)

[Rybags]

I don't think 32k x 1 or x 4 bit chips actually exist.  Generally DRam ICs have equal # of rows/columns which would give sizes:

 

R/C Size

4    256

5    1024

6    4096

7    16384

8    65536

 

Though some 800 Ram boards used partially failed DRams which only used half their capacity, not sure how the R/C arrangement was set up there.

[gs80065xe]

So each chip stores 1 bit of each address between 0 and ffff? Does that mean each chip is tied to only one line of the data bus.

[+kheller2]

Each chip stores one bit of the data bus D0-D7 for every address in a 800XL.  

[Rybags]

In theory if you could install only 32K then an XL would work with it in similar fashion to the old 400/800.

 

The OS establishes a contiguous RAMSIZ value based on multiples of 4K so should work with any memory size 4K to 64K.

4K was the original specification for the 400 and of course would be a barely usable configuration - no Dos, any graphics mode needing over about 2.5K would fail and you'd be lucky to type in a program that took much more room than 1 screen worth of listing.

 

The Acorn Electron I believe has 32K and is done so by combining 2 lots of 4 bit output from a 64k x 4 DRam on successive cycles to obtain a byte.

[shoestring]

Maybe you can use this type of SRAM on a daughterboard to replace the 4 bit rams in the 600xl and XE machines.

 

It's for the c64 but I can't see how this wouldn't work in an Atari computer.

 

 

[Rybags]

In theory you could, though generally SRam uses a different pinout and usually direct addressing rather than row/col so isn't an instant plug/play situation.

 

Since SRam needs no refresh it would be possible to make an extra circuit that prevents the memory refresh cycles halting the CPU - some logic needed there since /Halt is also used for screen DMA and that has to remain in place (Antic provides /Ref which allows distinction between the 2 types)

[Tickled_Pink]

10 hours ago, gs80065xe said:

I was wondering if you ever needed to replace ram in an 8-bit and didn’t want extra ram, would the Atari work with only 2 32K chips? For example, Remove all 8 chips in a 65XE. Then install only 2 41256-15 chips.

Having read Rybags' earlier comments I realised my mistake in mine. Yeah, these are 32Kbyte chips.

Thinking about it, I'm sure my non-working 65XE has 256kbit RAM chips in it.

Edited April 7, 2020 by Tickled_Pink