[HECnet] SIMH VAX Project

[Johnny Billquist]

On 2011-07-02 11.57, Mark Benson wrote:

On 1 Jul 2011, at 17:37, Johnny Billquist wrote:

On 07/01/11 09:33, Mark Benson wrote:

On 1 Jul 2011, at 07:46, Johnny Billquist wrote:

RA92 is 1.4G.

I think 1.6GB is the unformatted size, 1.4GB after initialize.

Well, the unformatted size is actually even bigger, at around 1.9G. But who cares about that? It is not something you can ever see or use.

Is it important for the size of the RAW virtual disk though? I haven't established of the virtual disks in SIMH need to be large enough to contain the unformatted size of the disk they are emulating?

No, they should not. The raw unformatted size is not something that is *ever* visible outside of the disk, and when you emulate the disk, you are not emulating the unformatted magnetic platters, but a block formatted device.

Since SIMH creates standard disk files itself I guess it's not a big issue. I am just curious though.

Curiousity is good. The thing you emulate is the thing that is visible at the disk contoller layer. So anything beyond that will (probably) be different from the thing you emulate. When you emulate a uVAX with an RA92 disk, simh will present you with a emulated KDA-50, on which there appears to be an RA92 connected. In the real world, the KDA-50 runs some sort of microcode, and communicates with the disk over SDI, which is a serial protocol using four coaxial cables. And the SDI protocol defines how the KDA-50 gets the RA92 to do all kind of operations.
But none of that is emulated, and there is no real point in emulating it. From the VAX point of view, you have the MSCP interface, as implemented by the KDA-50. And the emulated KDA-50 also gives you the MSCP interface. What happens beyond that is irrelevant, as far as the VAX is concerned. If it responds like a KDA-50 with an RA92 to the MSCP commands, then the VAX is satisfied.
And at that level, the RA92 is only going to show you 1.4G of disk. Always. Other properties are also true at this level. For instance, there are never any bad blocks.

And it's 1.4G after formatting, not initializing. (Atleast in DEC speak, where formatting is the low level formatting of the device, and initializing is creating a file system.)

Oh, okay. Fair point, I gotten used to stuff coming low-level formatted over the years. It's kind of a non-issue on modern systems! ;)

Not entirely. Sometimes you still want/need to do a low level format, but I agree that it is not as common, perhaps. Not that you needed to do it that much in the past either, but people still sometimes did, for various reasons.

[...]
So, you have a total blocks of 311200, which matches an RD54, yes. If your disk container is much bigger, and you haven't somehow gotten simh to restrict it, the total blocks number should match the hardware, so this would suggest that you got something wrong outside of VMS.

Yes, I agree the screw-up is in the SIMH config. What I'm not sure about is why SIMH, which had the disks configured as RAUSER (i.e. a user-defined size) value of 9600000 blocks (4.8GB at 512bytes per block) then reverted to using RD54 174MB disk sizes... odd. Perhaps I got the SET command wrong in the vax.ini I wrote, or SIMH interpreted the command wrong. I don't know.

It doesn't matter for now, I'm working with 3 RA92 images that do display the right capacity and I am up and rolling. I can telnet to a separate IP at any time and log right into VMS.

I don't know if this is a purely semantic point (i.e. because the security risk is in real terms negligible given it's a hobbyist machine) but should I be concerned about only having TELNET and no SSH? I used the Compaq TCP/IP 5.1 off the 7.3 CD-ROM. Someone mentioned a later version maybe? Does that have SSH?

Good to hear things are working now.
As for telnet vs. ssh. Well, ssh is safer, in that people can't sniff passwords easily over the network. If you worry about people doing that, then you might want to not use it. However, if your network is secure, then telnet isn't really an issue.
I don't think that Compaq have any version of SSH for VMS om VAX, but I haven't checked if anything was shipped after 7.3.
There are other options, though. tcpware comes to mine.

	Johnny