"jbender@ezol.com" "Jim Bender" wrote 
>>
>>The SDI bus be clocked at up to 22Mbits/sec or so with a max cable length of
>>maybe 80 feet (plus some allowance in the start and end cabs). The RA81
>>(introduced in 1982?) has a peak transfer rate of 17.4Mbits/sec and a capacity
>>of 456MB. By way of contrast the RA92 (1.5GB) runs at a peak transfer rate of
>>22.16Mbits/sec.
>
>Then why were they so damn slow even when connected to a "fast" VAX on a
>fast HSC or even a high end SDI controller?    So slow we were wishing we
>had our Massbuss disks back.    :-(

Assuming this isn't a rhetorical question:

Measuring disk "speed" with a single number is hard if not impossible. The peak
transfer rate is the best anyone could get shoving data downhill with a
following wind. You won't get anywhere near that in practice.

The RA81 had an average access time of 36.3ms (about the same as an RD54!). The
RA92 got that down to 24ms, the (SCSI) RZ29B is down at 12.2ms, the Fireball in
my PC is 9.5ms.

The same deal holds with these 32x, 36x, 40x CDROM drives. The earlier versions
had (relatively) poor access times, so they were not that much faster than a
good8x or 12x drive. The latest crop of 32x drives have access times in the
60ms region and feel much better (at least to me).

So what on earth possessed you to get rid of your Massbuss drives :-)

Antonio

Antonio Carlini                            Mail: carlini@marvin.enet.dec.com
DECnet-Plus for OpenVMS Engineering
Digital Equipment Corporation              Worton Grange, Reading, England