4 Mar
2007
4 Mar
'07
3:28 p.m.
Subject: Re: Copying DEC VAX set up disks rx50, help
From: "Dave Dunfield" <dave06a at dunfield.com>
Date: Sun, 04 Mar 2007 07:00:53 -0500
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
To affirm this, as exDEC RX50 is DD (250kbs).
Image Disk reads it with out errors
0/0: 300k DD 10 sectors of 512 bytes - G1:9 G2:17
0/1: Single sided
0/0: Single Step
800 sectors (800 data, 0 compressed, 0 unaval)
Read complete
Trying to write and it has errors from the get go.
0/0: 300k 10 sectors of 512 bytes
:format error <0> overun
:write error <2> no sector
and on .............................
written on a PC with 1.2 HD drive
Tried on another 1.2 and on a 360k drive
all capable of SD .
I tried both HD and DD disks . all bulk erased first.
Don't use HD disks - as ImageDisk noted in it's initial
report, all sectors in the image are double-density. You didn't show all the information, but since
it's
single-sided, 10 sectors per track, and there are 800
sectors, this tells me it's an 80 track disk.
So - don't use a 360K drive (they are only 40 tracks).
You shouldn't need to worry about SD capability - there
are no SD sectors in the image.
Correct The RX50 drive is a dual spindle single head
positioner 80 track (96tpi) drive.
The 300k data rate tells me that you recorded this on
a
1.2M HD drive - I'm assuming you did not specify a 300-250k
data rate translation when you recorded it (?)
It's not 300 data rate it's 250!
Assuming all that, it should write back to a 1.2M HD
drive
with ImageDisk. It should also write back to a 80 track DD
drive such as TEAC-55F or SA-460 or TM-100-4. You would need
to set a 250->300k data rate translation to write on a DD drive.
I don't have any VAX disks to try, however I have read and
written Rainbow disks, which are also RX50 and use 80 tracks
by 10x512byte sectors, so I know ImageDisk works with this
format.
VAX, Rainbow and otehr DEC RX50 media are all the same save for
the filesystems. The only other DEC 5.25 formats are RX180 (Robin
aka VT180 which is 40 track single sided DD 180k) and Vaxmate
(286 PC like) that used the RX33 drive for standard PC 1.2mb
format.
There is a VAX RX33 format that was found in microVAX2000 or
RQDX3 controller for QBUS systems [must be late firmware on
the MSCP sontroller]. That format was a flavor of 1.2mb PC
format and also did RX50 using FD55GFR (aka RX33 drive). Older
firmware RQDX-1/2/3 controller only did RX50 format.
10x512byte sectors can be twitchy on some PC setups.
It
pushes the limits of the drive and formatting more than
the standard PC formats do. Most systems which use 10x512
have a more flexible FDC than the PC does.
Some suggestions:
- Clean the heads and make sure the drive is working OK.
Format a floppy on your PC, then read it with ImageDisk
and see if all sectors can be written.
** Don't bother looking at any other suggestions until your
** drive is verified to be operating 100%
- Make sure you are using a recent copy of ImageDisk (you
can get the latest from my site). Some of the older
versions had trouble with gap calculations, especially
on "tighter" disks.
- Try another PC (not just a different drive).
Important as PC controler vary in implmentation at the subtle level.
- Try making one of the Rainbow images from my site -
this
is the same format.
NOTE: My images reflect the true data rate of the target
system (250k), so you will need to set a 250->300k
data rate translation to write them on an HD drive.
If this works, then there may be a problem with the
imaes you have created - send me one to look at.
- Check your drive speed. If it's high, try slowing it to
exactly 360 rpm - if it's "bang on", you might try slowing
it by 5-10 rpm - this can help if your PC is marginal at
the gaps required for 10x512.
This works and can help greatly.
Also make sure the PC is trying to run the 1.2mb drive at 300rpm
and NOT 360 or switching to 300kbs while using the nominal 360rpm
as NEITHER WILL WORK. RX50 is NOT 1.2mb mode its a 80track flavor
of DD (400k per disk single sided). This is a foreign format
and requires forcing the PC hardware in many cases. I cheat
I use a FD55E (96tpi, single sided 360rpm only) as then the PC
cannot force 300 rpm.
- Look at the calculated gap sizes, and try reducing
them
slightly. You shouldn't need to, but it's worth a try - PCs
are "highly variable".
;) you got that one nailed.
I don't have VAX disks to try, but I've just
successfully made
one of my Rainbow images using ImageDisk 1.14 and a HD drive.
The speed test shows my drive at 359 rpm.
Rainbow RX50 and VAX RX50 are same on disk low level format.
The filesystems are very different but if your reading sectors
(raw) then they are identical. I may add that XXDP(x11 diags)
on RX50 and RT-11 on RX50 also share that common media level
format.
In DEC parlance RX50 refers to 80tracks, 96tpi, single sided
with 10 sectors per track and 512bytes persector formatted
at a data rate of 250kbs @360 rpm. It also refers to the drive
known as RX50.
Hole this clears up some misconceptions.
Allison
5 Mar
5 Mar
2:03 p.m.
The 300k data
rate tells me that you recorded this on a
1.2M HD drive - I'm assuming you did not specify a 300-250k
data rate translation when you recorded it (?)
It's not 300 data rate it's 250! Also make sure the PC is trying to run the 1.2mb drive
at 300rpm
and NOT 360 or switching to 300kbs while using the nominal 360rpm
as NEITHER WILL WORK. RX50 is NOT 1.2mb mode its a 80track flavor
of DD (400k per disk single sided). This is a foreign format
and requires forcing the PC hardware in many cases. I cheat
I use a FD55E (96tpi, single sided 360rpm only) as then the PC
cannot force 300 rpm.
300k does not mean HD:
300 rpm & 250kbps = DD (or SD if MGM encoding)
360 rpm & 300kbps = DD (same bit density)
360 rpm & 500kbps = HD 1.2M PC format
300 rpm & 500kbps = HD 1.44M PC format
Most PC 5.25" HD drives do not do 300rpm - they always run
360rpm and the controller uses 300kbps data rate. If it were
HD it would be 500kbps.
ImageDisk does not know or care what kind of drive is attached,
and when analyzing the disk, it has no preconcieved notion of
what it should be seeing - it scans all available densities and
data rates and determines what it can read - that is why ImageDisk
files do NOT have an indication of "drive type" - ImageDisk doesn't
know about drives - only what it can see and manipulate at the
controller (as noted in a previous email, I an considering changing
this as it confuses some people, but at the moment, ImageDisk does
not think in terms of "drives" - it thinks in terms of density and
data rate).
When reading 96tpi DD disks, I use a Teac-55F which is a 300rpm
DSDD drive. This gives me the native 250k date rate the way god
intended :-)
In DEC parlance RX50 refers to 80tracks, 96tpi, single
sided
with 10 sectors per track and 512bytes persector formatted
at a data rate of 250kbs @360 rpm. It also refers to the drive
known as RX50.
Sorry, but that doesn't make sense - 10x512 DD format is done
at 250kbps / 300rpm - standard double-density. PeeCee HD drives
will do it at 300kbps / 360rpm. I am not aware of any DD formats
that use 250kbps / 360rpm, Although ImageDisk should handle this
if the drive can ... (Chuck?)
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html
3:38 p.m.
On 5 Mar 2007 at 17:03, Dave Dunfield wrote:
Sorry, but that doesn't make sense - 10x512 DD
format is done
at 250kbps / 300rpm - standard double-density. PeeCee HD drives
will do it at 300kbps / 360rpm. I am not aware of any DD formats
that use 250kbps / 360rpm, Although ImageDisk should handle this
if the drive can ... (Chuck?)
I think I've got one in 8" that does this--it's single-density, so so
the data rate really is 125Kbps. If you're really curious, I can dig
some and find out. The 2.8" sorta-floppies used in the SCM PWP's ran
at a data rate of something like 62.5Kpbs, but I wouldn't consider
that a "real" floppy--more like a streaming tape laid out on a floppy
cookie.
Cheers,
Chuck
4:19 p.m.
At sometime today, Allison wrote:
It's not 300 data rate it's 250!
Well, let's see what the numbers say.
360 RPM is 6 revolutions per second or 0.167 second/revolution
300 RPM is 5 revolutions/sec or 0.200 seconds/rev.
Thus, the raw capacity of a 300 RPM drive at 250Kbps is 50,000 bits
or 6250 bytes. The raw capacity of a 360 RPM drive at 250kpbs is
41667 bits or 5208 bytes.
On the RX50, since there are 10 sectors of 5120 bytes, we have
6250-5120 = 1130 bytes for gaps and ID marks, CRCs, etc. on a 300 RPM
drive. On a 360 RPM drive, one has 5208-5120 = 88 bytes for all that
overhead. Not considering gaps yet:
There are 10 bytes for a IDAM: A1 A1 A1 FE cc hh rr nn cr cr, where
cc is the cylinder number, hh is the head number, rr is the sector
number, nn is the sector length code and cr cr is the CRC for the
IDAM. To that, add the data preamble of 4 bytes A1 A1 A1 FB and a 2
byte CRC and you have (without gaps) 15 bytes per sector or 150 bytes
for a 10-sector track--and we're out of space already at 360 RPM
before we can add the barest of gaps (e.g. 12 bytes of 00 preamble
for the IDAM, 12 bytes of 00 preamble before the DAM...
You just can't do it at 250Kpbs and 360 RPM. Heck, 10x512 is a
fairly tight fit at 300 RPM.
Cheers,
Chuck
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