[TUHS] Booting PDP-11's from RX02's

[Don North]

On 10/29/2016 2:32 PM, Ron Natalie wrote:
> I think just like everything else the boot rom just pulls in the first
> sector of the disk.   I had RX02s on many of the BRL Gateways (my
> implementation that replaced your MIT Gateway while you were in exile).
> We put a V6 file system and I must have had a regular V6 boot block on it
> with a RX02.   There might be someone still at BRL who might remember where
> this stuff is.   I certainly don't have it.
>
> BRL PDP-11 kernels had both V6 and V7 file systems in them but I'd have to
> believe I was booting off a V6 one.

For RX01 (and RX02) the hardware bootstrap reads track 1 sectors 1, 3, 5, 7
into memory. For RX01 with 128B sectors this yields 512B total (just like reading
one 512B block from most other disks). Their is a fixed 2:1 sector interleave.

For RX02 is does the same sector reads, but since the sectors are 256B the total
amount of data read is 1024B. In reality only sectors 1, 3 need be read, but the
bootstrap (M9312 anyway) just goes ahead and reads all four sectors always.