[Simh] porting RL01 images to RL02

[Paul Koning]

> On Feb 5, 2017, at 7:55 AM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> I'm not entirely clear about what you mean by "porting".
> 
> Are you talking about getting the files and file system across from one type of device to another? If so, it might depend on the file system in question, but for the ones I can think of, in general, you can just copy the content to a larger device and it works just fine. You will not get access to the extra space though, as the existing file system only knows about the blocks that existed when it was created.

For RSTS, that's often not true, for two reasons.  One is the "cluster size".  There's the device cluster size and the pack cluster size.  The former is the power of two such that device size in blocks divided by that cluster size is <= 65536.  The pack cluster size is the file system allocation unit.  It must be >= the device cluster size.  If you put a small device file system on a larger device, it may have too small a pack cluster size.

The other, more limiting, issue is that the free cluster bitmap (file [0,1]satt.sys) must be large enough for the device the file system sits on.  If the pack cluster size still works for the device in question (for RL01 vs. RL02 that would always be true) you may well have a bitmap file that's too short for the larger device.

Both of these issues will cause the OS to complain when you try to mount the file system.

	paul