The Acorn System Computers never had the option of Winchester disks, given the high cost of Floppy drives at that time I wonder what a Winchester disk drive would have cost ? However Winchester disk based products did become available for the BBC/Master Computers and the FileStore.
BBC/Master
Acorn produced two Winchester disk drive products for the BBC and Master Computers:
Model 110 with a capacity of 10Mbytes
Model 130 with a capacity of 30Mbytes
These units where interfaced to the computer using the 1MHz Bus and where accessed using the ADFS Advanced Disk Filing System.
The Winchester drives use the Seagate ST-412 interface and were controlled via an Adaptec ACB-4000 Winchester disc controller, this provides a SCSI bus interface. The connection between the SCSI bus and the Acorn 1MHz bus was then provided by Acorn's own SCSI Host Adapter Board. The units also included their own mains power supply.
The following documentation applies to these products:
(Disc or Disk - convention for computer products is generally Disk and that is what I prefer to use however Acorn seem to have used both spellings !)
FileStore
FileStore was Acorn's Level 3 Econet File Server, it came in two variants: the E01 and E01S. The E01 came as a basic machine with Floppy drives only but could be expanded by adding an E20 20Mbyte Winchester expansion unit. The E01S base unit included the SCSI interface and could have up to four Winchester drives connected, two drive capacities were available:
E40S with a capacity of 40Mbytes
E60S with a capacity of 60Mbytes
Acorn SCSI Host Adapter Boards
Acorn have several designs of SCSI Host for interfacing between a processor bus and SCSI though they are all based on the same circuit:
Acorn SCSI Host Adapter Board
Acorn AIV Host Adapter
FileStore E20 Winchester Disc Host Adapter (the E01S incorporates essentially the same circuit)
Here are the schematics for each board:
Whilst the three circuits are functionally similar there are some important differences:
the Acorn SCSI Host Adapter connects to the BBC/Master external 1MHz Bus interface and is therefore addressed at $FC4x.
the AIV Host Adapter connects to the Master's internal 1MHz interface and is addressed at $FE8x, also note that the data is inverted. This board is intended to be used with the Doomsday system and will not work with ADFS.
the FileStore E20 Host Adapter connects to the FileStore bus and is addressed at $FC3x.
Winchester Disk Format
Winchester disk's provide a number of disk surfaces laid out in tracks and sectors in much the same way as Floppy disks.
I've tried to determine the disk parameters for the various drives used by Acorn and included them in the following table (still draft):
| Product |
Nominal Capacity [Mbytes] |
No. of surfaces (heads) |
No. of
cylinders (tracks per surface) |
No. of
sectors per track |
No. of bytes per sector |
Formatted Capacity [bytes] |
Drive | BeebSCSI Image |
| Winchester Disc 110 | 10 | 4 | 306 | 33 | 256 | 10,340,352 | ||
| FileStore E20 | 20 | 4 | 306 | 61 | 256 | 19,113,984 | RODIME RO652 | |
| Winchester Disc 130 | 30 | 6 | 640 | 32 | 256 | 31,457,2801 | RODIME RO203E | |
| FileStore E40S | 40 | 5 | 680 | 47 | 256 | 40,908,800 | RODIME RO3057S | |
| FileStore E60S | 60 | 7 | 750 | ? | 256 | ? | RODIME R3085S |
SOFTWARE
The Acorn Model 110/130 included a suite of utilities that were included on the drive:
CATALL
EXALL
WEDITOR
COPYF
BACKUP
SUPERFORM
I believe all except WEDITOR are the same as the version on the Master Welcome Disk, I'm still looking for a copy of WEDITOR ?
Acorn SCSI Implementation
For at least their 8-bit computers Acorn used an early implementation of SCSI, SASI (Shugart Associates System Interface) which was then apparently renamed SCSI (to avoid using a company name) later becoming SCSI-1 when later implementations were added. SCSI-1 includes a subset of SASI so should be backwards compatible.
There are a number of features of SASI that vary from the more widely used SCSI protocols.
In particular SASI allows for non-arbitration in a single Initiator (computer) system, this means that the usual Arbitration Phase can be omitted and the Initiator can start communications with a Selection phase. This means that you will see communications start by activation of the SEL line rather than the BSY line, the BSY line being asserted by the Target in response to its Id on the bus.
ADFS appears to output an ID of 2 in the Selection Phase regardless of which drive (0 to 3) is being accessed. (The Adaptec Controller in the Winchester 130 is set to SCSI ID 0 i.e. no links fitted.)
