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From: dempson@atlantis.actrix.gen.nz (David Empson)
Subject: Re: Apple][ SCSI
Message-ID: <D5sE3y.7FJ@actrix.gen.nz>
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Date: Tue, 21 Mar 1995 10:50:22 GMT
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In article <3kk85k$jve@sue.cc.uregina.ca>,
charles macdonald <macdon@HERCULES.CS.UREGINA.CA> wrote:
>
> Does anyone out there know if I'm limited to the 128M in 4 partitions
> on the Apple][ SCSI or if there is some way around this limit.
It really depends on the partitioning software. With the software
supplied with the original Apple SCSI card, you can only create two
partitions (64 MB in total). With the software supplied with the
high-speed card, you can only create four partitions (128 MB in total).
If you can get a third-party utility which can create more partitions
(or find someone nearby who has the necessary software and can do this
for you) then you can go up to seven partitions (224 MB) with the
original SCSI card, or at least nine (depending on the partitioning
software) with the high-speed card.
You will usually be limited to 11 partitions in total on all drives,
because there are only 11 spare entries in the ProDOS drive table
(assuming a 128k machine, one 5.25" controller and no other disk
drives or standard slot RAM cards).
Nine partitions would be 288 MB, eleven would be 352 MB.
To be able to use more than four partitions with an Apple SCSI card,
you must be running ProDOS-8 2.0.1 or later, which requires an
enhanced IIe. With earlier versions, you can only get four partitions
if the SCSI card is in slot 5. If it is in another slot, you will
only be able to access two partitions.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand
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From: dempson@atlantis.actrix.gen.nz (David Empson)
Subject: Re: Disk Format
Message-ID: <D5y9Ez.325@actrix.gen.nz>
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Date: Fri, 24 Mar 1995 14:54:34 GMT
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In article <3kpf4o$387@senator-bedfellow.MIT.EDU>,
Paul H Bauer <pbauer@ATHENA.MIT.EDU> wrote:
> I am trying to find out the physical arrangement of data and directory
> information on a disk partition and where it is located on the disk.
On an unpartitioned disk (e.g. a small hard drive, or a floppy), the
logical block numbers correspond to the physical block numbers. The
boot block is at physical block 0, the directory starts at physical
block 2, etc.
In detail, the first few blocks on a ProDOS volume are:
0 Boot block (boot code)
1 Unused (can contain Apple /// boot code on a 5.25" disk)
2-5 Root directory
6-N Volume Bitmap (free space list)
The first entry in the root directory contains the volume name and
size in blocks. The size of the volume directory is determined by the
number of blocks on the disk. One block is required in the volume
bitmap for every 4096 disk blocks (8 bits per byte times 512 bytes
per block).
The data area starts immediately after the bitmap. Subdirectories,
file data blocks and file index blocks are scattered throughout the
remainder of the disk.
On a partitioned disk (assuming we are talking about Apple's SCSI
partitioning), physical block 0 contains the "device descriptor map",
which is used to locate Macintosh device drivers. The partition table
starts at physical block 1, with one block per partition (there are
usually several unused blocks at the end of the partition table, to
allow for more partitions to be added). The partition table is
regarded as a partition, and requires one entry in the partition
table. Every user partition (e.g. ProDOS or HFS volume), device
driver and free area also requires an entry.
Each subsequent partition is a contiguous range of blocks on the
drive, starting immediately after the previous partition.
When you access a partitioned drive from ProDOS or GS/OS, you never get
to see the DDM or partition map - you can only see the logical blocks
within the partitions. If you ask for block 0, you will get logical
block 0 of the partition, which contains the boot code as normal.
Accessing the DDM or partition map requires special calls to the
device driver or SmartPort firmware. This is much easier under GS/OS
with Apple's drivers, because they have provided calls for this purpose.
Under ProDOS-8 with an Apple high-speed SCSI card, the only way to read
the partition map is to use the "Generic SCSI" call to do a direct SCSI
READ operation on the appropriate physical block range. This is NOT
easy, and requires the technical reference manual for the HS SCSI
card, and documentation on the SCSI command set.
With the original Apple SCSI card, it is even harder, because you have
to download code to do the SCSI READ into the memory of the SCSI card,
and arrange for it to be run from there.
I have no idea how you could access the partition map with a RamFAST
(either from GS/OS or using the SmartPort firmware).
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand
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From: nparker@cie-2.uoregon.edu (Neil Parker)
Newsgroups: comp.sys.apple2
Subject: Re: where on the disk is ProDOS partitioning information stored?
Date: 1 Nov 1995 09:29:19 GMT
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In article <4736uv$7qt@aplinfo.jhuapl.edu> Robert Jensen
<bob_jensen@jhuapl.edu> writes:
>When a ProDOS disk is partitioned into multiple volumes, where
>and how is the partitioning information stored? Or, where and
>how is the answer to my question stored?
The answer to your question is stored in several different places--the
Apple IIGS GS/OS Device Driver Reference, and Inside Mac (both the old
version--around volume IV or V, I think--and the new black version).
The Inside Mac documentation is more complete than the GS/OS Device Driver
Reference.
Apple's standard partitioning scheme is currently supported only for SCSI
disks. A partitioned disk starts with a "Device Descriptor Map" located
at the beginning of physical block 0, which has the following layout:
Byte Purpose
---- -------
0 (1 byte) signature, always $45 (ASCII "E")
1 (1 byte) signature, always $52 (ASCII "R")
2 (2 bytes) device's block size, in bytes
4 (4 bytes) number of blocks on device
8 (8 bytes) reserved
16 (2 bytes) number of driver descriptors following
This structure may optionally be followed by one or more driver descriptors,
which describe the locations on disk of any Macintosh device drivers on
the disk. Each device driver descriptor has the following layout:
Byte Purpose
---- -------
+0 (4 bytes) starting block of device driver
+4 (2 bytes) size of device driver in blocks
+6 (2 bytes) driver type (1=Macintosh)
A disk used on an Apple II need not have any device driver descriptors
at all, but such a disk will not be recognized on a Macintosh.
The Partition Map starts in physical block 1, and contains one block for
every partition on the disk. Note that the Partition Map itself is a
partition, and must have an entry in the Partition Map (but physical
block 0, containing the Device Descriptor Map, is not part of any
partition, and has no Partition Map entry).
Each block of the Partition Map contains exactly one Partition Map entry
which describes the characteristics of a single partition, including the
partition's starting block address and length. Partition Map entries
are a bit lengthier than what I feel like typing in tonight...I recommend
reading the GS/OS Device Driver Reference or Inside Macintosh for the
full details.
- Neil Parker
--
Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker
"Evolution is vastly overrated." -- Ambassador Delenn, _Babylon_5_
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From: dempson@atlantis.actrix.gen.nz (David Empson)
Subject: Re: where on the disk is ProDOS partitioning information stored?
Message-ID: <DHIu2o.I2n@actrix.gen.nz>
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Date: Sat, 4 Nov 1995 13:42:24 GMT
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In article <47dr6r$hrv@gap.cco.caltech.edu>,
Nathan Mates <nathan@cco.caltech.edu> wrote:
> In article <4736uv$7qt@aplinfo.jhuapl.edu>,
> Robert Jensen <bob_jensen@jhuapl.edu> wrote:
> >When a ProDOS disk is partitioned into multiple volumes, where
> >and how is the partitioning information stored? Or, where and
> >how is the answer to my question stored?
>
> It's not located anywhere within the partitions themselves; scsi
> retains a few blocks as a sorta directory of contents for the disk.
> Only by some very low-level scsi commands to go out to disk, and read
> the partition table directly can you get at it.
>
> I've never seen this info documented; your best bets might be
> either some very technical scsi manuals, or disassembling partitioning
> programs.
The partitioning scheme used on Apple II and Mac is documented in the
GS/OS Device Driver Reference, and also in the Inside Mac series. (In
the original series, it was covered most fully in Inside Mac Volume 5.
I haven't seen the newer versions, but it is probably in the same
manual that documents the SCSI Manager.)
In short, the partition map resides on the first few physical blocks
of the hard drive.
Physical block zero contains the "device descriptor map", which
contains information used by the Macintosh to locate the device
drivers on the disk.
The partition map starts on physical block 1. There is one block used
for each partition map entry (usually with several unused blocks to
allow further partitions to be added). Each entry indicates the
physical location and size of the partition, and the type of data
stored in the partition (any of "partition map", "driver", "free", or
a specific file system). The partition map is itself counted as a
partition - all blocks from 1 to the end of the disk must be listed in
the partition map.
On the Macintosh (at least, in older machines), the boot code in the
ROM doesn't know about partitioning - all it knows is how to read the
device descriptor map and to locate the device driver. This is read
into memory, and takes over for further accesses to the drive. One of
its first actions is to read the partition map into memory.
On the Apple II under ProDOS-8, the SCSI card firmware is responsible
for dealing with partitions. When the system is booted, the SCSI card
looks at the drive to see if there is a partition map (there are
specific ID bytes at the start of each entry). If not, the drive is
assumed to be unpartitioned, and is treated as a single volume. If a
partition map is detected, it is read by the firmware, and a logical
volume is set up for each ProDOS partition. Other file systems and
other types of partitions are ignored. (With the Apple High-Speed
SCSI card, at least one volume is always created, even if there are no
ProDOS partitions. I don't know how the RamFast and original Apple
SCSI card act.)
Subsequently, ProDOS-8 (through the driver on the SCSI card) treats
each partition as a separate volume. It has no knowledge of the fact
that the volumes are partitions on the same physical drive. The
driver on the SCSI card only provides access to the blocks within the
partitions, so you do not have direct access to the partition map
(unless special calls are used).
If you re-partition the drive, the partitioning software reinitializes
the SCSI firmware, which causes the partition map to be re-read, and
volumes to be reassigned if necessary.
Under GS/OS (with an Apple SCSI card), the SCSI Manager and drivers
take over all access to the SCSI drive once they have been loaded.
SCSIHD.Driver deals with the partition map, and as with ProDOS-8,
allows access to each file system partition on the drive (it obviously
recognises HFS and ProDOS partitions, but I'm not sure how it would
react to another file system, such as A/UX). As with ProDOS-8, direct
access to the partition map requires the use of special calls (this is
much easier under GS/OS with the Apple drivers than it is under
ProDOS-8).
When you repartition the drive with Advanced Disk Utility, special
driver calls are used, which causes the driver to re-read the
partition map, as with partitioning software under ProDOS-8.
There is sufficient documentation in the GS/OS Reference + GS/OS
Device Driver Reference + Programmer's Guide for System 6.0.1 to be
able to write your own version of ADU (for use with the Apple SCSI
drivers under GS/OS).
It is a different matter under ProDOS-8. You need the technical
reference manual for the appropriate SCSI card (I don't think the
manual for the original Apple SCSI card is available any more, but
Byte Works might be able to supply it).
With the Apple High-Speed SCSI card, you also need documentation on
the SCSI command set (the SCSI-1 and SCSI-2 standards), as access to
the partition map involves a "direct SCSI" call to the firmware,
using a SCSI READ call with the appropriate block range.
With the original Apple SCSI card, there is a special option provided
by the firmware which disables the normal partition mapping, and
allows direct access to the physical blocks on the disk using the
normal SmartPort BlockRead and BlockWrite calls.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand