Note: If you have a working Lt. Kernal system and simply want to
Add another drive:
- You'll still
need to understand the information cover below and on the "Editing SYSGEN"
page
- Edit your SYSGEN disk with new drive parameters, and
- Then, install the modified SYSGEN DOS software
Adding or Replacing Drives:
This section
describes the procedure for adding or
replacing Hard Drives to the Lt. Kernal system.
Also discussed are Drive Enclosures
and connecting the Host Adapters' Non-Standard
SCSI-1 output to the drive via a special
SCSI Adapter assembly. Lastly, it is strongly
recommended that you read the information
covered in both the SYSGEN and HARD DRIVE
sections before modifying your Lt. Kernal
because this data will help you understand
how to maximize the Kernals' storage
capacity.
Many SCSI hard
drives will work with the LTK, but not
all. We'll describe how the hard drive 'parameters'
or 'specs' determine which Drives
are compatible and how & why these
drive parameters are entered into the
SYSGEN DOS software. As explained below,
the drive data must be entered into the SYSGEN
software in order for the system to properly
recognize the drive. Unlike a modern PC or Mac,
the Commodore and LTK don't have the ability
to interrogate the drive (auto-install) and
store the drive parameters by themselves.
So, you need to manually enter this data
into the SYSGEN software.
Since the original
Fiscal and Xetec system design used
external hard drive enclosures to house the
drive(s), we'll also look at some
options you can adapt to your Lt. Kernal
system. Other than the drive enclosure
containing its own power supply for the
drive, there's nothing special about the
external case. However, connecting the
enclosure to the Host Adapter has raised
questions in the past, so we'll cover this
issue as well.
As mentioned
previously, this series of articles only
addresses the Xetec Host Adapter designed for use with embedded-controller
SCSI hard drives. Fiscals' (and Xetecs')
older and less common designs, which use
OMTI controller cards, are not covered in
this section.
To pick a SCSI
Drive for use with the Lt. Kernal, you'll
need to lookup the Drives':
- Number of HEADS
- Number of
SECTORS/TRACK
- Number of
CYLINDERS
- Can the
drives' Parity be disabled
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Selecting
a Hard Drives:
Many Lt. Kernal
systems were shipped with either a 20 Meg
or 40 Meg MiniScribe, SCSI-1, embedded
controller Hard Drive. Those MiniScribe 'stepper-motor'
hard drives make a distinctive sound
during self-test at startup! Image
what it must sound like to have seven Miniscribes
crammed into an external enclosure?
Xetec also offered
an ADD-ON drive option. Xetec would send
you another external drive case (with
drive) and a new/modified original SYSGEN software
diskette. Your new drive would be
set to SCSI address "1" (to go along with
your existing address "0" drive) and the
new drive Parameters added to the next
sequential drive-table cell position on
your new SYSGEN disk. All you needed to do
was daisy-chain the new enclosure in your
system and reinstall your new software. Of
course, your old copy of the original SYSGEN
would be useless because it wouldn't know the
new drive existed! Needless to say, this software
dependence on Xetec probably helped kill
the product. But the information in this article
will remove your dependency on the non-existing
company.
So, what if you
don't want to add another Miniscribe Hard
Drive? Moreover, why would you want to use
this unreliable and slow drive anyway? Xetec
used the Miniscribe because they
were cheap and common for the 1980s.
However, you don't have the restriction of
80's technology and can used thousands of
compatible drive now! Besides, the slew
rate and transfer rate of the old
Miniscribe drives makes them an undesirable
drive given the choices you have in newer drives.
As long as the
drive is SCSI compliant and has some other
common features, you can use a HH 3-1/2"
Seagate/Quantum/Sun/Apple/etc. or a FH 5-1/4
Prime/Micropolis/etc. or many other
drives. As a matter of fact, if all you
have are 1 gigabyte drives, they will work
just fine! Whatever drive or drives you
pick for the Lt. Kernal, there is a limit
to the total megabyte capacity you can
use! Xetec said in the Manual that the
limit was 140 Meg, but this was mainly do
to their use of 20 Meg drives. Just keep
in mind that regardless of the Drive capacity,
the Lt. Kernal only understands how many Cylinders,
Heads and Sectors/Track are programmed/entered
into the SYSGEN software. Therefore,
if you use a 1 gigabyte hard drive, you'll
only program the number of Cylinders, Heads
and Sectors/Track that will equal the maximum
limit of the Lt. Kernals'
capacity.
The Host Adapter is
designed to use 'embedded controller' SCSI
hard drives. The "N" type (Narrow, 8-Bit) 'embedded'
SCSI drive is the most common (cheapest)
and easiest to integrate into the Lt.
Kernal. While Narrow, 8-bit drives are no longer manufactured,
these drives are readily available online for less than $10.00. Here
are some drive parameters to look for when
choosing a hard drive for use in the
Lt. Kernal:
- "N" type (embedded) 50-pin
SCSI hard drives
- 1 to 10
Heads
- Cylinder
count from several 100s to 1500
- 15 to 40
Sectors per Track
As you can see,
this includes a Bunch of drives. It really
doesn't seem to matter about manufacturer's
brand. It also doesn't matter if
the drive contains a computer manufacture's
Boot ROM (e.g., Sun, Apple, etc.). To
start with an example, let's look at a Seagate
ST1201N. First, it's an 'embedded' drive
and has:
- 9 HEADS
- 1068
CYLINDERS and
- 36
SECTORS/TRACK
Here are some
other drive characteristics you must
consider when choosing a SCSI drive:
- Choose drives with selectable
jumpers for 'Start Unit' (i.e. drive
motor starts without commands)
- Okay to use
Apple (Mac) or Sun computer
drives that contain special Boot ROMs.
- Drives with
selectable 'Parity'. Usually, the LTK
does NOT like Parity Enabled with small
drives!
- The Host Adapter does
Not use the Parity line. Therefore,
since the Parity line is 'floating',
the drive controller may think there
are continuous Parity Errors, unless
Parity is Disabled on the Drive
Controller.
- Example,
Quantum ELS Prodrives Won't work (no
way to disable Parity)
- Quantum LPS
Prodrives Do work (because you can
remove Parity jumper -
disable)
- If you choose
a variable Sectors/Track drive, ALWAYS
use the lowest number
- Example: Maxtor LXT-213SY
(Sun) has 34-56
Sectors/Track (depends on where the
Head is located on the
Disk).
- On a PC,
default interrogation of the drive
shows 42 Sectors/Track (average)
which, if used on the LTK, will not
work. But, by setting to 34
(lowest value), the same drive
works fine.
- Variable
Sectors/Track drives were not
available when the Lt. Kernal was
designed, so it was never a design
consideration and why it is not
talked about in the Manual.
- If all you
have are one gigabyte drives, they work
great with the LTK
- No, you won't get a
Gig of storage, but the drives are Fast
and cheap!
- You'll have
to de-tune the drive (use less
Cylinders, Heads, Sectors/Track
numbers) when you edit the SYSGEN disk.
- Just
because the drive has more
Cylinders/Heads/Sectors, you just
don't use them all!
- The LTK only knows
what you program (which is very
convenient!)
- Generally,
higher capacity drives have higher
slew, seek & data transfer
rates
- Big speed difference
compared to a Miniscribe!
- Whenever
possible, check the drive specs online
or in a drive 'bible' with the data
returned by your PC or Mac formatting
program (as above).
- LAST Drive
MUST BE TERMINATED! Follow normal SCSI
termination procedures
- Un-terminated drives will either operate
unpredictably or not be seen by the
Host Adapter.
- Yes, if you
use 2 or more drives, only Terminate
the drive furthest from the Host
Adapter.
- Termination Power must be supplied by the Drive, Not the
SCSI Bus!
- With multiple drives,
power the bus on the Last drive.
The Lt. Kernal
only needs Three pieces of drive parameter
data. The reason for this is that
Cylinders (most data you can fetch without
moving the Head), Number of Heads and the
number of Sectors per Track, defines how
much data can be stored on a drive. If you've
looked-up the drive data and determined the
drive parameters, the Sectors/Track number and number of
Heads are numbers directly entered into the SYSGEN
software. However, even though the number
of Cylinders generally ranges only in the
thousands and could be easily entered, the
Cylinder number is entered into the SYSGEN
software in HI Byte/LOW Byte
format. Why? Any number greater than 256 won't fit into
an 8-bit byte.
HiByte/LoByte
isn't all that complicated to understand,
but needs to be discussed here. In our
Seagate ST1201N example above, this drive
has 1068 Cylinders. So, if we divide the
number of Cylinders by 256 (HiByte), we
come up with 4 (1068/256=4.xxx). Then, if
we multiple 256 times 4 and subtract that
product from 1068, we get 44
(1068-(256*4)=44) or the LoByte. These two
numbers (4 and 44) are the representative
cylinder numbers entered into the Kernals'
SYSGEN Disk.
Now that you've
gone to all the trouble of calculating CSH
data, it'll never be directly used by the
Lt. Kernal. Other than this data being
stored on the hard drive for bootup, LTK DOS uses
the drive parameters to convert to Physical
Block addressing. Block addressing is used
when LK DOS assembles a SCSI Command
Descriptor Block in the Commodore which is then passed
through the Host Adapter to the drive
controller.
When looking
for hard drives and calculating drive parameters, keep in mind
that the Lt. Kernal can only use a maximum of about 150meg (per
drive) of the drives total capacity (at any given time). The
ideal drive size is between 160 Meg and
200 Meg. However, I prefer to use 1 gig drives because these drives
are faster and cheaper, even though I'll waste most of the drive's capacity.
(Is there a way to use more of the drives capacity? - Yes!) Regardless
of the drive capacity, the secret to more Lt. Kernal storage
capacity is to use more than one
drive!
Whatever the
storage, we're
talking about an 8-bit Commodore.
Commodore programs typically range from 10
to 200 Commodore Blocks in size. That
means you can store thousands of Commodore
files in a relatively small amount of
space. So, whatever hard drive you choose
to use with the Lt. Kernal, you can add enough
megabyte storage capacity and never run out of drive
space!
The bottom
line is that it's easy to find a compatible
drive that will work with the Lt. Kernal system!
Once you selected a drive (or drives) and
have determined the drive's number of
Cylinders, Heads and Sectors/Track, you're
ready to edit the SYSGEN software.
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