Notes On Choosing A Disk Drive; Notes Regarding Scsi; Appendix 1 - Akai DD1500 User Manual

APPENDIX 1

NOTES ON CHOOSING A DISK DRIVE

You will probably have bought your system with a disk drive installed. If, however, you are
supplying 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 DD1500 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 DD1500 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 maintain 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. The result may be that
you might get 16 tracks when you start using the drive for the first time but, as you fill up
your disk and start using material from further into the disk, you may only be able to
achieve 10 tracks (or less!). Look out, therefore, for 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
sixteen disk tracks.
As a result of all of this, Akai cannot guarantee that you can just hook up any SCSI drive
and expect it to work. It is impossible for Akai to test every drive in the world as there are
so many to choose from. However, as more and more people use the DD1500 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 DD1500m 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
terminated.
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
Page 278 Version 2.00 - March, 1996