Conference hydra::amiga_v1

    I meant :-
    
    What is An A2090A ?
    

    
>    can someone explain (in laymans terms) what is an SCSI drive? What
>    is an ST506 drive?
 
ST-506 and SCSI are not *drives* per say. They are the INTERFACE to the drive.
ST-506 is the first generation interface on the small winchester type drives. 
It is a real dumb 2 cable connection which requires a significant (relativly)
piece of hardware which can step the heads, generate a low level
sector format, read and write raw data, separate data from headers etc. It
is inherently limited to a 5Mbit transfer rate. Data is written/read in serial
format.

SCSI stands for Small Computer Systems Interface.
SCSI is a single cable (SCSI 1, anyway) 8 bit parallel "bus". I say bus in that
there is a defined protocol using 9 control signals and 9 data bits (1 is parity).
All of the "controller" functionality is now placed in the drive. A host system
sends "commands" which may be 6, 10 or 12 bytes in length. Data transfer is
done 8 bits (1 byte) at a time and consists of DATA only - no header information
as with ST-506. Data is also accessed as "Logical Blocks" as opposed to
head,cylinder,sector that st-506 uses.

SCSI data transfer can be anywhere from (theoretically) 2-4 MBYTES/second.

SCSI-2 will provide a 32 bit bus and (with fast mode synchronous) up to 40MBYTES
per second!

One distinct advantage of SCSI over ST-506 is the ability to add other devices
to the same bus (i.e. tape drives, printers, optical drives, scanners...)

   
>    I have, at my disposal, and RD32 (which I is an ST-251 drive), which 
>    will fit in the 5 1/2" slot on my A2000. What do I need to connect up 
>    so that my Amiga can use it (including software) ?
 
An ST-506 controller or a SCSI adapter with a SCSI to ST-506 adapter.
Something like the A2090(?) from Commodore would do. There are SEVERAL.
Look in a recent Amazing Computing for an intense review on A2000 hard drives.
   
>   What is an A2092 ?

AutoBooting A2090???
    


John

    Since you have an RD32, I would recommend you get the A2090 or A2090a.
    This controller has a built in SCSI to ST506 adaptor.  You could
    then mount your RD32 (1/2 ht drive) in the  5 1/2" drive bay.  If
    you purchased any other controller, you would have to add a SCSI
    to ST506 adaptor such as the Adaptec A4000 or A4070.  You would
    have to kludge up some type of bracket, since there isn't enough
    room below the drive to mount it there. It would have to go on top.
    Do-able but potentially messy.
    
    By the way, the RD32 specs are:
    
    Typical Formatted Capacity:  42 MB
    Unformatted Capacity: 51MB
    Drive Height:  Half
    Average Access Time:  48.3 ms
    Maximum Transfer Rate: 625 KB/s
    Power Consumption:  13.2 Watts  (.95A @ 5v   .65A @ 12v)
    Number of Heads: 6
    Number of Cyl:  777
    
    By the way, if you use an RLL controller (A4070) instead of a MFM
    Controller (A2090, A2090a, A4000) you can push the drive from 40MB
    to 60MB.  This is drive specific, since your drive was probably
    certified for MFM operation.
    
    Hope this helps,
    
    John
    
    

    That's nearly all I need to know except :-
    
    How much is An a2090, or A2090a (what is the difference), and what
    cables will I need to connect the drive to the controller?
    
    re. 2 thanks for all the info, it was very helpful. i now understand
    alot more of what others are talking about
    
    Martin

John, RD32 has 820 cylinders (0-819) not 777  :-)

Not sure if it will work with RLL, but for 20 more Mb's it certainly worth
a try!

John

    re: .5
    John,
    
    Thanks!  I'll update my spec list.  I can always use a few extra
    tracks!  
    
    John
    

At 17 sectors, You were only losing about 2Mb - Whats a couple floppies, huh?

John

         A few more HD questions...   I have read most of the hard drive
    notes, but was wondering what are the main factors in overall
    performance.
    
         In real usage is a 28ms (access time) drive noticeably faster
    than, say a 40ms drive?  It would seem to me that transfer time
    would be most important, and that is based on what type of controller
    you are using (and on the drive, also).
    
         I would like to find a good price/performance combination.
    Originally I had thought of getting a fairly fast access 20Meg drive,
    and adding as needed.  Now, after looking through ads, I am leaning
    towards getting the ST227 65Meg 40ms access drive. ( I may not need
    65Meg of storage right now, but the price-per-meg for that drive
    really seems good. )
    
         There are also an increasing number of SCSI controllers.  Any 
    comments/suggestions about particular ones?  DMA/non-DMA, Hard Frame,
    Hard Cards, Memory/Disk controllers, etc, etc.  
    
         I really don't have much experience using a HD in a small computer
    environment, so... I would appreciate any/all help.

    Steve - With new Amiga stuff consisting of a Mitsubishi AUM-1381, 
            MC68010, and patiently waiting for Lattice C v5.0

Average access will be more apparent for seek intensive applications.

It may be more noticable under the Slow File System which seeked all
over.

John