On 9/28/17 10:21 AM, Geoffrey Oltmans wrote:
On Wed, Sep 27, 2017 at 11:16 AM, allison via cctalk
<cctalk@classiccmp.org <mailto:cctalk@classiccmp.org>> wrote:
IDE disks format usually meant high level only. SCSI could be
either depnding on the specific controller and media.
Seems like the omission of low level formatting of IDE drives had more
to do with preserving the servo track data, (and maybe aforementioned
firmware/bad sector data) yes?
IDE was supposed to be near plug and play so low level formatting was
not required and undesired.
With that most did not low level format, just leaving room for the
likely exceptions. The key was the drive interface was embedded on the
drive to remove the need for a board in the bus.
Even IDE cam in flavors, LBA, bus interface speeds, then large LBA types
as we know them now.
That also includes the CF cards as they had an IDE mode as well as 8bit
data bus interface mode.
Its all PATA... (IDE, EIDE, ATAPI...)
SCSI/SASI was the exception for all. It ws a system to device interface
and the endpoint could be a drive controller with formatting capability
and a raw ST506 drive or it could be a Drive very similar to IDE
(Embedded Disk Electronics) with a SCSI interface. Again I've used all
flavors, CP/M (Micromint SB180
with SCSI adapter) and Xybec controller to a 20mb ST225, PC with Adaptec
and D540, microVAX with
CMD SCSI (bus card) and M3100s with internal SCSI and RZxx type drives.
Were any earlier MFM/RLL voice coil/servo controlled, or were they all
stepper drives?
YES to all. The early drives came in all flavors. SA412(10mb) was
stepper, Quantum D540
was voice coil with embedded servo yet it could be reformatted (RQDX1/2
and RQDX3 had
different formats and I've used the same after formatting on
Teltek(CPM), PC (1003MFM and
1005-RLL controllers), plus my PDP11s/MicroVAX (RQDX3 andRQDX2) which
are all very
different. Generally Drives of the MFM or RLL (ST506/412) interface
were low level formatted
though exceptions existed.
There was a lot of evolution in disks within the PC world some ideas and
developments
originated from outside that and others were exported. SCSI and MFM
interfaces were
from outside PCs realm and added in and IDE was uniquely PC in origin
though it was a morph
of the "host controllers" which were bus level interfaces similar to but
not IDE.
For a few years you could get the same controller for a MFM drive that
could have
Host interface, SCSI, IDE, and all the various PC busses (MicroChannel,
ISA8, ISA16, EISA a and more),
and then buses from DEC, DG and others. That list is far from complete
but serves the example.
Allison
