Ted asks:
> Doesn't MPE deal with 4096-byte pages now?  Does the blocking factor
matter?
> How does changing it change the efficiency of the storage or of the
retrieval
> of the data.
>

Several people have already answered, so I'll just try to summarize. The
blocking factor on MPE/iX is primarily used as a means of compatibility with
MPE/V. It comes into play in two situations:

 1) When using the STORE ;TRANSPORT option (to create tapes in the MPE/V
    store tape format)
 2) When reading a file that has been opened with either NOBUF or MRNOBUF

In case 2, above, the blocking factor is used to insert fill characters into
the "block" of data that is returned to the caller, so that it looks exactly
like it did on MPE/V, when data actually was stored in a block-by-block
basis.

On MPE/XL and now MPE/iX, data is stored with each record laid out
"end-to-end". The blocking factor is not relevant.

Now to the performance question. The answer is, (drum roll please) "It
depends."

No, really, it does! For buffered and NOBUF access, it makes no real
difference. For MRNOBUF, it can make a difference. The idea behind MRNOBUF
is to retrieve multiple blocks of data in a single system call, therefore
saving on the overhead associated with multiple calls to FREAD. This is
offset by the fact that the file system is doing extra work to pad the data
being returned so that it looks as if the data had been stored in blocks. So
the larger the number of blocks read (in your MRNOBUF read), and the less
efficient the blocking factor, the more overhead that you have per each byte
of real data moved.

So in the one case of MRNOBUF access, it is best to try and specify a
blocking factor which allows the least amount of "wasted space" per "block".

Hope this helps!
Craig