Page 98
DD8
plus Version 2.20 - September 1998
NOTES ON CHOOSING A DISK DRIVE
You will probably have bought your DD8 with a disk drive installed. If, however, you are supply-
ing your own disk drive, please bear the following in mind.
Theoretically, any disk drive that conforms to the SCSI implementation may be used with the
DD8 and you will get more or less tracks and time depending on the speed and size of the disk.
Basically, any modern disk drive should work - in fact, with the speed of current hard disks, it
would be difficult to find a drive that didn’t give a fairly healthy number of tracks! It is only with
older drives you may experience performance problems but, even then, the DD8 will try the best
it can to get as many tracks off disk as possible. You should be able, therefore, to connect any
SCSI drive and it should work.
However, please be wary of a few things. For a start, don’t take for granted the specifications
given in brochures for disk drives. They may quote quite fast access speeds but they may not be
strictly accurate and many of them quote ‘best case’ figures. Also, buying a disk drive with a fast
access speed is not a guarantee of achieving lots of tracks as data bandwidth (i.e. the data
transfer rate - usually expressed in Megabytes Per Second) is also crucially important and a
slow drive with a high bandwidth may give better results than a disk whose access speed is
quoted as being extremely fast. One other point to bear in mind is that some disks do not main-
tain a constant bandwidth across the disk and you will find that some drives are very fast at one
end of the disk but extremely slow at the other. The same may be true of disk access speed.
Beware of specifications that quote “average” figures for disk speed as they may not give you a
true indication of what the disk is capable of across the whole disk. Furthermore, different drives’
SCSI implementation can vary quite dramatically. In our tests, a drive with an access speed of
around 10 milliseconds and a transfer rate of around 3Megabytes per second should be able to
give eight disk tracks.
As a result of all of this, AKAI professional cannot guarantee that you can just hook up any SCSI
drive and expect it to work. It is impossible for AKAI professional to test every drive in the world
as there are so many to choose from. However, as more and more people use the DD8 and try
out different drives, we will gradually find out which drives give the best performance, which
drives are not really suitable and which drives just cannot be used. As this will vary from country
to country, you should speak to your local distributor about which drives are recommended.
NOTES REGARDING SCSI
The DD8 communicates with disk drives using SCSI so, as mentioned elsewhere in this manual,
you must be aware of some restrictions imposed by SCSI.
1
Every device (i.e. every disk drive) on the SCSI chain MUST have unique SCSI IDs.
Failure to observe this will cause problems and unreliability. The maximum numbers of
disks you can have on-line at any one time is seven (SCSI ID#0-6).
2
The recommended TOTAL LENGTH of the SCSI chain must not exceed 6 metres.
3
It is important to install the correct termination. Usually, the rule is that the first and last
devices in the chain must be terminated and all devices in between should not be termi-
nated.
4
Always use high quality SCSI cables. Cheap ones may seem an attractive proposition
but can cause unreliability. Cheap, unscreened SCSI cables may also introduce unwanted
noises into your audio system, especially if audio and SCSI cables are in close proximity to
each other.
Failure to observe any of the above can result in problems and unreliability.
However, assuming your system is set up correctly, you should have no problems. If you have
any doubts at all, please contact your local distributor who will be able to help and advise you.
APPENDIX - 1
