Virgo Amiga 2M Ram expansion - Any info about it ?

dougal

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As some of you may know, yesterday I got my hands on an A500. Yes another one. I've now got around 9 A500/500+ Amigas.

It came with a SupraDrive 500XP (52mb HDD + 4MB Fastram) a Zip Stick, 2 mice, A520, RGB to 1084S and RGB to Philips.

It also had another surprise in the trapdoor slot.

A Virgo Developments 2M Ram expansion. There is the expansion with a wire leading to I think the Garry (did not remove the metal cover to see).

I can't find any info at all about this card.

Sysinfo reports:

4MB Fastram (That is onboard the SupraDrive 500XP - Please ignore)
1.0MB Slow ram
512K Chip ram

My question is, why is it called "2M" ? and why would 1MB Slow ram need a wire leading to the Garry ?
 
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roy_bates

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can you take some pictures of the card?

thats so we can see how much memory is on it.

gary probably has an adaptor under it to access the extra memory,these type of card dont generally work in 500+'s
so it would a little if you could tell us what revision the 500 is,its probably the revision 5 or 6 i would guess,there was lots of cards around for this at the time.
 

dougal

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Here you go :)

75e05e87584f2f480146856fc1547e1b.jpg

fc795941d6d63b33ac95208834ccc06d.jpg

834aba4d82740e40c1e3383c706f7861.jpg
 

roy_bates

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yeah it has got 2mb on it.

do you have anything other than that card plugged in to alter memory? if not its working properly...

i was expecting more than one wire going to gary though for some reason.also not sure if some of the memory can be used as chipram..some can

EDIT: can you take a wider shot as i cant see where all the wires go.
 
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dougal

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How do you mean ? Right as in the pic just the A500 Rev 6 with the trapdoor card and Garry adapter. Workbench 1.3 loaded from floppy disk. Nothing else
 

dougal

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SysInfo says 1.0mb Ram slow and 512K Chip

Avail in CLI says 512k chip and 1.8mb Fast

I'm sure i'm correct in saying Sysinfo got it wrong and CLI is right.

- - - Updated - - -

Also wondering, should I remove the battery ? No signs of leaking but the previous owner said this Amiga has been in storage since around 1996/1997.

Its not quite a barrel battery
 

roy_bates

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if the battery charges up fine i would leave it be.

its up to you if you remove it or not.
 

BLTCON0

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SysInfo says 1.0mb Ram slow and 512K Chip


Avail in CLI says 512k chip and 1.8mb Fast


I'm sure i'm correct in saying Sysinfo got it wrong and CLI is right.


The card has 2 MB in 4 distinct 512 KB blocks. 4 chips per block.


Block #0: $C00000 - $C7FFFF (512 KB)
Block #1: $C80000 - $CFFFFF (512 KB)
Block #2: $D00000 - $D7FFFF (512 KB)
Block #3: $D80000 - $DFFFFF (512 KB)


But it also has an RTC, which sits at $DC0000


So Gary will block accesses to the $DCxxxx range, and this limits block #3 to $D80000 - $DBFFFF (256 KB).


So the total slow/ranger RAM available is 3x512 + 256 = 1792 KB = 1.75 MB


CLI (avail) reports the same thing: 1827608/1048576 = 1.743 MB (and not 1.8 ).
The slight loss (0.007 MB) is due to some AmigaDOS (exec) structures (jumptables etc) having been already stored in this RAM area at the time avail was executed.


Also wondering, should I remove the battery ? No signs of leaking but the previous owner said this Amiga has been in storage since around 1996/1997.


Its not quite a barrel battery


It looks like a supercap, so no real danger there.


As for the wire, it's actually two wires.
Since the card uses 4 x 512 KB blocks (of which only one at a time can appear "connected" to the trapdoor), it must be informed (by the Gary adapter which "listens" to the address bus) which of the 4 that should be, depending on the address currently used.
Two wires = Two binary signals (0 or 1) = 4 possible combinations (00, 01, 10, 11).
So 00 = use block #0, 01 = use block #1, 10 = use block #2 and 11 = use block #3.
 
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