[Info-vax] RMS internals?

[glen herrmannsfeldt]

In comp.os.vms Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
(snip) 
> Just because other systems allow records greater than 32K does not mean 
> that files have to be written with records that big.
 
> The only format that is close to being universal is fixed length 80 byte 
> records.  Many systems can block and/or deblock those fixed length records.

The 80 byte records are especially popular with IBM systems, though
the block size is usually more.  Many compilers can only read 80
byte records.  The second most popular is 133, for 132 character
printers plus carriage control.  

For disks on MVS, the user also chooses the block size, similar
to the way it works on tapes on other systems.  Normally the block
size must be less than or equal to the track length.

> Either the tapes must be written with record lengths < 32K or they must 
> be read on another system!!

There was a story of someone writing a whole tape as one block using
data chaining on S/360.  If the channel is fast enough, or the device
is slow enough, you can write a single block with multiple channel
commands (CCWs).   Otherwise, OS/360 and successors have a maximum
of 32767.  (Signed 16 bit arithmetic.)

-- glen