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How much memory

V

vladstamate

Experienced Member
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Dec 2, 2012
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Orlando, FL, USA
Hi all,

I am trying to figure out how much memory I have in my PDP-11/23. The individual (gold) chips are TMS4164. A quick Google search indicates that they are 64kilobits each. There are 32 of them so that would make 256KBytes of memory. Is that a normal amount for a PDP-11/23 system?

memory board

If one wants more memory one adds another memory board to the system or can there be just one memory board? In case of multiple memory boards, do they have to be same size?

Regards,
Vlad.
 
Yes, 256KB is a fairly normal amount for a QBus 11. Though having only 32 chips on the board instead of 36 means there's no parity check...but then, you're probably not running a mission-critical system on this thing!
 
Hi,

As you are probably already aware, I am also a newbie with DEC equipment...

The TEXAS INSTRUMENTS TMM10010-05 board is advertised as 256K memory board, but that may mean 256K bytes, which would be 128K words for a PDP-11. Your calculation seems correct to me, that 32 chips would make for 256K bytes, or 128K words. The picture you posted shows 8 chips missing, and that bothers me a bit. I'm not sure if they would be there for 18 bit words, so you may only have 16 bit words? As you probably already know, the PDP-11/23 should be able to operate as an 18 bit machine.

Anyway, that is a very reasonable amount of memory for a PDP-11/23 (mine has only 64K words and I have already asked that question, and I have already gotten that same answer). To add more, all you need is another memory board. It does not have to be the same size as the one you have. You simply have to address the additional board at the appropriate location above your existing memory, via jumpers or dip switches, or whatever means is provided by the board.

I hope this helps...

smp
 
smp said:
The picture you posted shows 8 chips missing, and that bothers me a bit. I'm not sure if they would be there for 18 bit words, so you may only have 16 bit words? As you probably already know, the PDP-11/23 should be able to operate as an 18 bit machine.
Click to expand...
The PDP-11 doesn't have an 18-bit mode of operation; it is always 16-bit. The extra two bits per word are parity bits (not sure if it uses one per byte, or a word-wide 2-bit checksum.) But that would only require four extra chips; I'm not sure what the other four sockets are for...
 
smp:

Thank you very much for the information! Seems like adding more memory is quite simple and I can use my existing card too, which is good.

commodorejohn:

Is it possible that the extra 4 slots (so 8 extra) are there in case you have double capacity memory chips, maybe?

I hope bitsavesrs has the manual for this specific card. I would like to verify if the jumper/switch configuration is correct.

Regards,
Vlad.
 
commodorejohn said:
The PDP-11 doesn't have an 18-bit mode of operation; it is always 16-bit. The extra two bits per word are parity bits (not sure if it uses one per byte, or a word-wide 2-bit checksum.) But that would only require four extra chips; I'm not sure what the other four sockets are for...
Click to expand...

OK! I apologize for the error. Can you please enlighten me about why I see references to 18 and 22 bit operation? Does it have something to do with whether or not one has the FPU option, or something to do with the MMU? Or, is it something to do with other models of PDP-11 or another bus besides the Qbus? As a newbie with DEC equipment, I am quite overwhelmed with the amount of documentation available, and sorting through which is applicable and which is not is a daunting task.

Again, sorry for speaking out of turn on this.

smp
 
Oh, right. 18- and 22-bit in that case refer to the width of the address bus, not the word size. 18-bit systems can access a maximum of 256KB memory, and 22-bit 4MB (as compared to the original 16-bit address bus's 64KB.) All three modes exist on various QBus 11s, while (IIRC) the only Unibus 11 to support 4MB is the 11/44. The MMU does play into it, since even in larger modes the 11 only uses 16-bit addresses, so various portions of the extended address space have to be mapped piecemeal into the CPU's native 64KB.
 
Q16 vs Q18 vs Q22 is related to memory addressing. In order for us to tell you how much memory you can put in your 11/23, you need to tell us the etch revision of the M8186 processor. Yes, you do need the MMU to make use of more than 32kW of memory, but I never saw an M8186 without one. Scan the front and back of your M8186 and post it and we will tell you what etch revision / ECO level and then we can tell you if it's Q18 or Q22. Depending on your backplane, there may also be some bussing to be added to upgrade the backplane from Q18 to Q22.

On a side note, my lowly 11/04 has the maximum 32kW of core and does run RT11-SJ and FB just fine. It is usable running Basic-11. I have even have a DEUNA in this 11/04 and can run the TCP/IP package for RT-11 and use FTP. So there's a lot that can be done in 32kW.

Lou
 
18- and 22-bit operation refers to the /addressing/ mode. It specifies the number of physical address lines available for memory addressing. Some PDP-11s have MMUs, which allow switching in and out greater amounts of memory than physically addressable, or segmenting memory with different privilege.

The memory addressing capabilities of a system, bank switching aside, are determined by the address bus width. Some PDP-11 processors were further restricted to 16-bit address buses (IIRC the LSI-11/2 CPU is) and can only address 2^16 locations. While the PDP-11 uses a 16-bit word, memory is bytewise-addressed, so a 16-bit address space addresses 64 KB of memory, not 64 Kword.
 
Commodorejohn, Lou, Glitch,

Thanks a million, guys, for all your help and information. This is greatly appreciated. I see now the mistake I was making - more address lines only means more memory can be addressed, but the data word is always 16 bits wide. I suppose I should have been able to figure that out on my own, but with all the different documentation covering all the different configurations, along with my newness with DEC equipment, well, let's say it is tremendous fun learning all this, but it is a bit like drinking from the proverbial fire hose.

Again, thanks so much for all your patience and gentle attention and advice!

smp
 
Last edited:
Lou - N2MIY said:
Q16 vs Q18 vs Q22 is related to memory addressing. In order for us to tell you how much memory you can put in your 11/23, you need to tell us the etch revision of the M8186 processor. Yes, you do need the MMU to make use of more than 32kW of memory, but I never saw an M8186 without one. Scan the front and back of your M8186 and post it and we will tell you what etch revision / ECO level and then we can tell you if it's Q18 or Q22. Depending on your backplane, there may also be some bussing to be added to upgrade the backplane from Q18 to Q22.

On a side note, my lowly 11/04 has the maximum 32kW of core and does run RT11-SJ and FB just fine. It is usable running Basic-11. I have even have a DEUNA in this 11/04 and can run the TCP/IP package for RT-11 and use FTP. So there's a lot that can be done in 32kW.

Lou
Click to expand...

You GO buddy! For those that don't know, Lou is an unqualified MANIAC (in a great way)... DEUNA in 11/04. Didn't you have a UDA50 in there too at one point?

Everyone's correctly distinguishing address bus size. 18 bit max is 128KW (256KB) and 22 bit is 2048KW (4MB). The 11/23 DUAL wide CPU can be either 18 or 22 bit. (I have both myself) However in addition to what's already been posted, making an 11/23 operate in 22 bit mode has more than just the CPU and backplane involved. The memories and modules have to be 22-bit compatible too. It's a bit of research to do by P/Ns. A shortcut is to power the system and see what mode the CPU comes up in. Of course if you don't have a properly configured system - this could be dangerous. Only do this if you are absolutely certain it was usable when last turned off, and that nobody has molested the card placements and settings.

I don't know that TI memory, but is seems likely that it's configured as non-parity 256KB / 128KW. It would be configured for Parity by adding the missing chips and some setting changes. It does confuse me a little being there are 8 chips missing (parity is usually one bit per 8-bit byte) but if you find documentation it will answer these questions.

Incidentally - parity is usually signaled on bits 17 and 18 on the databus during 16-bit data transfers.
 
Yeah, the UDA50 and DEUNA are both still in there. I think the T-11s on the UDA50 and DEUNA may be more powerful than the 11/04. I do now have an 11/34a boardset (unsure if they work) so at some point I will start working on upgrading. If they are broken, it will be interesting to work on (likely far more difficult than the 8/e CPU though).

Lou
 
I thought that the 8186 KDF-11 card is what makes the system an 11/23? And that the KDF-11 without the MMU can only address 32K and with MMU 128K and the 22 bit address stuff along with all the larger cards were all newer or higher series systems?
 
Qbus said:
I thought that the 8186 KDF-11 card is what makes the system an 11/23? And that the KDF-11 without the MMU can only address 32K and with MMU 128K and the 22 bit address stuff along with all the larger cards were all newer or higher series systems?
Click to expand...

You are missing the fact that early revisions of the MMU and the board itself, were only good to 18 bits. People thought the QUAD 11/23+ was the only 22 bit. Later versions of the 8186 were quietly upgraded to 22 bit capability. I was unaware of this until I accidentally installed one in my VT-103 which was modified to Q22. When it saw all the memory (4MB), I was astounded.

Later, it became common knowledge, though it didn't make it into service docs for a while.
 
Lou - N2MIY said:
Yeah, the UDA50 and DEUNA are both still in there. I think the T-11s on the UDA50 and DEUNA may be more powerful than the 11/04. I do now have an 11/34a boardset (unsure if they work) so at some point I will start working on upgrading. If they are broken, it will be interesting to work on (likely far more difficult than the 8/e CPU though).

Lou
Click to expand...
If those T-11's had a MUL instruction, they would be! (They have no MUL or DIV)

So... do you have cache for that 34? Sooo cool if you do. Speaking of 04's... what is it about them... do they always travel in the company of a 34? (I have both too)

Ya - probably a challenge - but you're up to it. ;)
 
RSX11M+ said:
You are missing the fact that early revisions of the MMU and the board itself, were only good to 18 bits. People thought the QUAD 11/23+ was the only 22 bit. Later versions of the 8186 were quietly upgraded to 22 bit capability. I was unaware of this until I accidentally installed one in my VT-103 which was modified to Q22. When it saw all the memory (4MB), I was astounded.

Later, it became common knowledge, though it didn't make it into service docs for a while.
Click to expand...

For the curious, the long ECO / etch revision history of the M8186 is documented in Micronote 17.

Etch revision C supprts Q22. Etch rev A at any ECO level does not. (There is no B etch.)

Lou
 
> So... do you have cache for that 34? Sooo cool if you do. Speaking of 04's... what is it about them... do they always travel in the company of a 34? (I have both too)

I also have an 04 and 34(a). My 34 has the FPU, but I've never been able to find a cache card for it...

Ya - probably a challenge - but you're up to it. ;)[/QUOTE]
 
Roe said:
> So... do you have cache for that 34? Sooo cool if you do. Speaking of 04's... what is it about them... do they always travel in the company of a 34? (I have both too)

I also have an 04 and 34(a). My 34 has the FPU, but I've never been able to find a cache card for it...

Ya - probably a challenge - but you're up to it. ;)
Click to expand...


I have no cache card either. Frankly, I'm just lucky to have the processor.

The 11/34 is a dead easy upgrade from an 11/04. They use the same backplane. The 11/04 (single card processor) goes in the very first slot and the memory in the second. In an 11/34, the two board processor occupies the first two slots. Basically, to upgrade from 11/04 to 11/34 (or /34a), you just push everything out and make room in the second slot for the second board of the processor.

I am always up for a good challenge. I love working on hardware and I really don't care how long it takes me to fix something. This evening I went to radioshack and bought a $2 thermal fuse so I could fix my $20 clothes iron.....

Lou
 
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