And in particular Atari's SH204, 20 Megabyte hard disk
WHAT IS A HARD DISK?
A hard disk is the optimum development of the
floppy disk. A floppy disk, like the 3½ inch disks used on the Atari
ST, is a thin disk of plastic, covered with a thin film of a
magnetic material similar to that used to make audio and video
tapes. The amount of data that can be reliably stored on such a disk
is limited by several factors, but mainly the speed of rotation. In
the case of floppy disks, the spin speed is about 300 rpm and the
head is in contact with the disk, which gives a reliable storage
volume of about 1 megabyte (as on the Atari double sided drives).
Some of the storage limitations of the floppy are caused because
they are removable, i.e. if you want to do word-processing, you
normally put in the 1stWord disk, if you want to communicate, you
put in the faSTcom disk (waddyamean 'plug plug'??). The problem with
this is that dust and smoke particles can get on the disk surface
making dense data storage unreliable but the floppy is normally able
to survive because the head simply pushes the dust out of the way.
The hard disk however spins at a much higher speed
(typically 3, 500 rpm) and due to this speed increase the read/write
head can 'fly' over the surface. The disk has to be rigid (hence
hard) as any variation in the position of the disk in relation to
the head could cause damage to both. This provide a much greater
data density on the same sized disks. To ensure reliability, a hard
disk is enclosed in a vacuum, as a speck of dust would not be pushed
out of the way of the head, but would plough up the disk surface (a
head crash) and make it unusable. Hard disks with 10, 20, 40 and 120
megabytes from both 5¼ and 3½ inch sizes are currently available.
WHAT USE IS A HARD DISK?
Considering it gives you twenty megabytes or more
of storage, instantly available, need I answer this? Not only more
storage, but greater access speed too. According to the manual, the
SH204 transfers data at 5 megabits per second. It's a big and
impressive figure, but let me put it in perspective. A friend of
mine reckoned that I could do a two pass compile and link in the
time it took his computer to just load the first pass of the
compiler from his floppies (and the ST's floppies aren't slow!). A
slight exaggeration perhaps, but an indication of the apparent
speed.
To the user who has a large amount of data to
store (e.g. in a big database), the serious software developer (e.g.
when the object code gets too big for one floppy), or a bulletin
board operator (for large message bases), a hard disk is invaluable
in order to save time.
HOW IS A HARD DISK USED?
Very easily. If you can use the floppy based
system, you will find a hard disk easier. The SH204 comes packed in
a thick foam padded box, complete with the mains cable, DMA data
cable (18" long), manual and boot disk. In essence, it is simply a
matter of connecting the cables, copying the boot disk, and
following the manual instructions. Once connected up, the first
thing you have to do is format the drive. I found that mine was
pre-formatted, but I recommend that you do it yourself anyway.
HOW DO YOU GET THE BEST FROM A HARD DISK?
There is one complication with hard disks, and the
complication is called 'partitions'. A problem arises because twenty
megabytes (20Mb) is a lot of storage space. On a 1Mb or ½Mb floppy
disk, there is a finite (but reasonable) limit to the number of
files that can be stored but with 20Mb you can have far too many
files to be practically managed. It is for this problem that folders
(subdirectories) were devised, and they should be used on hard
disks, but a more fundamental solution is to split the 20Mb up into
two, three, or four 'logical' disk drives, called partitions. One
physical drive (device) you can have several logical drives. These
logical drives are named C:, D:, E:, and F: (if you have all four).
That may seem straightforward to you, and if that is the case then
all well and good, but if you cannot quite grasp the concept, read
it again, it is important.
The reason it matters is that when you format a
hard disk, you format the PHYSICAL device and not a logical drive,
thus if you decide that you no longer want the files on drive D:,
you cannot format it as this would lose files on C: too. Atari's
hard disk utility program (HDX - a GEM based program) allows you to
'psuedo-format' the logical drives with a 'zero' drive option. This
clears the root directory, wiping the drive clean, but leaving the
other logical drives alone.
Partitioning the hard disk will delete any files
on the disk too, but you can edit the partition scheme as you would
like it, or choose one of the predefined ones. Typical schemes are
10-5-5, 15-5, 10-10, 5-5-5-5, and you can choose your own (I use
8-4-4-4). If it is your first use of a hard disk, I would recommend
10-5-5 (i.e. C: is 10Mb, D: is 5Mb, E: is 5Mb) to start, but a
common method is to set aside a drive for each application you are
going to use, and a spare one for general use. (My 8-4-4-4 is
general, utilities, development-1, development-2).
The final option of HDX (the others were Format,
Partition and Zero), is Markbad. This is used only when you are
having problems reading from the hard disk. Just like a floppy, a
hard disk can have 'flaky' or unreliable sectors. The hard disk
keeps a record of these sectors so that they will not be used to
store data, and markbad is a way of adding any new flaky sectors to
the list. However, if any sector added to the list is in use by a
file, then that file will be lost, so you should back up the logical
drive before using markbad.
Having decided on your partition scheme, using the
partition is just the same as using a floppy disk, though thoughtful
use of folders is essential.
HOW RELIABLE IS A HARD DISK?
A hard disk is just as reliable as a floppy disk,
if not more so. With good treatment it should give many years of
working life. The main problem of with hard disks is that you have a
lot of files instantly accessible for deletion or corruption, should
you mistype a command or should a program go wild and out of control
(and it will happen!). For this reason you should keep regular
backups of all your important files (see below). You should also be
wary of new and untried programs. Whenever I buy a new program, I
always try it out first with the hard disk turned off. That way, if
it does go wrong, it cannot corrupt the hard disk. The most likely
'dangerous' programs are those with copy protection. Occasionally
software is programmed to erase disk if it thinks you have a pirated
copy. In the case of a hard disk, it has plenty to play with.
ARE THERE ANY SPECIAL PRECAUTIONS OR MEASURES TO TAKE?
As I have mentioned above, a hard disk spins very
fast, and the head flies just above the disk surface. Due to this,
even the slightest knock while it is turned on could cause the head
and disk to collide, thus destroying the disk. A hard disk should
not be moved while it is turned on. When it is turned off, it is
slightly more robust, and is suitable for gentle moving around the
room. To make it as safe as possible, ready for transport to another
building, you must 'park' the head. This is done with a (supplied)
program called SHIP which moves the head to a safe landing zone on
the disk, so that if it does get jolted no damage will be done.
The only other things to do are make regular
backups, and look after your hard disk as you should other
electronic equipment.
SHOULD I WAIT FOR THE BETTER VERSION?
If you hear of a better or cheaper version, you
have to weigh up the factors. At present, the SH204 is reliable,
fast and available. I have heard that a new version is coming out
which has two DMA connectors so that they can be daisy-chained like
the floppy disks (the ST supports seven DMA devices;. While that is
obviously a nice facility, to wait a few months maybe stretching
into several months) for it to appear is, in my opinion, folly. Buy
now and you have a few months of hard disk use, and when you buy
your second DMA device, buy the 'Y' adaptor that they will have to
sell for those of us with only one connector.
HOW DO I BACK UP A HARD DISK?
All through this review, I have stressed the
importance of making backups. but I have not mentioned how it can be
done. Backing up a hard disk is a problem because if you have twenty
megabytes of files, then you are going to need twenty 1Mb disks.
or 40 ½Mb disks. Also you have the trouble of copying the
directory, getting 'disk full' messages, and copying the rest onto
another disk. Restoring the files to the hard disk is just as bad.
There are two answers, tape spoolers, and backup
programs. Tape spoolers are DMA devices into which you put a
magnetic tape capable of holding at least 20Mb of data. With
appropriate instructions, the hard disk will start sending a
complete copy of itself to the tape spooler, and after five minutes,
the backup is done. Undoubtedly the fastest and best method, but it
is not yet available on the Atari. Several companies are promising
tape spoolers (they can be used for 'live' data storage too - but
slow) but none have yet been launched. I think the number of hard
disks sold must increase first. They are also expensive, often as
much as the hard disk itself.
Backup programs help by organising the copying to
or from floppies for you. In principle, you simply have to feed in
floppy disks, while the program crams as much as possible onto each
and then requests the next. An intelligent backup program uses a
'flag' set by TOS whenever a file is altered. When the backup
program copies the file onto the floppy, it clears the flag. If you
then change the file, TOS sets the flag and when you next do a
backup, the program need only copy those with the flag set. Next
issue I'll bring you a review of Microdeal's BACKUP program for more
detail on what backup programs can do.
DO HARD DISKS DETERIORATE?
You've heard the rumour too, huh? That, when the
hard disk is new it goes like the clappers, but after a few months
it takes so long to create a new file that it seems like a floppy?
Well the 'rumour' is true, it can happen. But not just to Atari hard
disks, it can happen to all hard disks (IBMs too!). The reason is
that when a hard disk is new, there is plenty of room, and nothing
occupying it. Each new file is given fresh, consecutive, space on
the disk which means it can be found and loaded easily. But, as time
goes on, you start to delete files, and the next time you create a
file, TOS fits it in the gap of the deleted one, and the next one
goes half in the gap, and half into the so-far-unused section. And
as this happens more and more, the whole disk becomes more and more
fragmented. After months of this, you have to forgive TOS for not
being able to find everything instantly, because the subdirectories
become fragmented too. As an aside, some Disk Operating Systems,
e.g. Acorn's DFS (sic) on the BBC, overcome this problem by not
using the gaps caused by deletion. It just continuously allocates
from the so-far-unused section. This means that while there may be
50k free on the disk, you cannot access it until you have done a
'squeeze' to move all the files into the gaps. Such a method may
seem the answer, but practice shows it is 'problematic'.
There is no neat solution, but if you find that
the response time is very slow, there is a way of fixing it. All you
have to do is delete everything. This clears the disk so that it all
starts consecutively again. To clear it quickly use the zero
partition option of HDX. If you actually wanted the files you had on
the disk, then either make a full backup, clear, then restore, or
copy all the files over to another partition (with enough free room
to take the files) and then copy them back after clearing. I have
only one worry when I do that sort of thing, and that is that a file
may become corrupted in the copy process and I thus lose it, but it
hasn't happened yet.
The Atari SH204 Hard Disk Drive costs £599 plus
VAT and is available from all Atari dealers.
NEXT ISSUE -
Microdeal's Hard Disk BACK UP utility. Taking the
worry away?
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