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1993-04-07
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Atari Classic 8-bit 400/800/XL/XE, IBM PC Hard Drive emulator - a review.
By Roger Lacey 11/01/93
For New Atari User (Page 6 Publishing).
Have you ever dreamt of hard drive capacity drives for your Atari Classic
400/800 XL/XE computer but balked at the thought of parallel bus host adapters,
SASI, SCSI, connecting leads, power units to suit, cost etc? Perhaps you have a
400 or 800 Classic with no parallel bus? Then this just may be the solution:-
Peter Welham's Hard Drive Emulator, HDEMUL, written for the IBM PC and
compatibles, seriously attempts to solve the problems of what a lot of Atari
Classic 8-bit computer users and enthusiasts have a need for:-
i. Larger capacity floppy drives
ii. Fewer piles of floppy disks adorning our worktops and shelves!
iii. A printer interface.
The HDEMUL does actually solve these problems quite neatly by acting as a file
server for your humble but powerful Atari8 computer, and an SIO printer driver
utilising any IBM PC or compatible - from an 8-bit XT to a 486 machine.
Atari
Officially, Atari's solution to larger capacity disk drives was the fussy XF-551
360K floppy drive. This can be upgraded (read re-built!) to accomodate a 3.5" or
5.25" 720K drive.
This solves data storage in two ways; by quadrupling the formatted capacity of
an enhanced 1050 drive, and in the case of 3.5" disks, being physically smaller
than their 5.25" counter-parts. You could probably buy a low end PC clone with
hard drive for the equivalent price of such a drive though!
SIO2PC
The principle of operation of HDEMUL is based upon a program and small hardware
interface pioneered by Nick Kennedy in the USA, named SIO2PC.
Briefly, this utilises the PC's memory to hold single or double density disk
images loaded from disk files in PC RAM, and behaves similar to a 1050 drive
albeit faster as there are no mechanical parts as the 'disk' is read. Printer
support is also provided. With the printer plugged into the PC, printing
initiated from the Atari may be fed through the PC to the printer with optional
Atari EOL to CR/LF translation necessary for text files. Optionally, printing to
the PC screen or a disk file can be chosen.
The concept of utilising a PC as a drive emulator is not really so strange. All
Atari drives are intelligent by nature and are driven by a CPU (6507) running a
program from ROM. The PC is a CPU running a program from disk in a similar
manor, simple!
The SIO2PC program allows up to four drives of this nature but is wholey
dependant upon the amount of memory available from the PC after the program is
run and consequently not all four drives are always available, and are limited
to a maximum size of 180Kb - the equivalent of a single sided double density
disk. Further, this has been released to the public as Shareware and attracts a
Shareware fee for the Author.
HDEMUL
HDEMUL takes this a stage further and substitutes memory accesses for drive
accesses very similar to the Xformer program for the Atari ST. (Xformer is a
complete Atari8 emulator for the ST though). The MSDOS file image on the PC
drive that represents the Atari disk is accessed directly by the program and
although not as fast as the SIO2PC memory access, is still faster than a
standard 1050. Also larger drive emulations can be utilised and is only limited
by the PCs hard drive capacity.
The user can choose between two types of drive emulation: -
1. The 1050 size floppy drive densities of Single (90Kb), Enhanced (120Kb), and
Double (180Kb).
2. Hard Drive sized 'floppies' of 1Meg, 5Meg, 10Meg and 16Meg.
The latter relies upon the fact that the PC's hard drive has the capacity to
support this size as the 'floppy' is in fact a disk image, as mentioned before,
stored and accessed directly from the hard drive as a bog standard MSDOS file of
the size chosen.
This allows HDEMUL such large capacity emulations as not many people have access
to 16 Megabyte of memory after they have booted up!
If the PC in question does not have a hard drive it is still perfectly feasable
to utilise the PC's floppy drive with HDEMUL but will only support up to a 1
Megabyte Hard Drive assuming a 1.44M drive, and of course several smaller disk
images can be accessed from this drive too.
The files produced by the aforementioned SIO2PC program are similar to the
smaller size (1050 drive) files produced by HDEMUL and so full compatiblity
between the two programs is preserved and allows swapping of files such that if
you started off with SIO2PC you will have complete compatibility.
Printer support is provided in a similar manor to SIO2PC.
Sector copies
All normal unprotected floppy disks can be sector copied or DOS copied onto disk
image files on the PC hard drive via HDEMUL. This means games, utilities and
anything without a disk protection scheme can be transfered and then booted from
HDEMUL by loading the image file to drive 1 (D1:). It then loads just as though
it were a standard Atari drive, provided that the standard drive is not switched
to D1: and ON, of course.
Up to eight of these image files can be loaded into eight drives within HDEMUL
and all of these are available at any one time - you don't even need a physical
floppy drive once all your software is transfered to disk image files! Want to
buy some used floppy disks?
'Hard Drives'
At the larger end, you might wonder what you would do with a 1 or 5 Megabyte
'drive' or larger? - Quite simply, you don't know until you get one! Arcing and
Unarcing becomes a breeze instead of a chore - no disk swopping. Cataloguing
becomes simpler - copy all the relevant files to one drive and sort them (DOS
permitting).
DOS
Speaking of DOS, there are only two Atari8 DOSs which support hard drives, MyDOS
and SpartaDOS. MyDOS is up to revision 4.53/3 and SpartaDOS in flavours up to X.
SpartaDOS 3.2 is the highest revision disk based DOS with X in cartridge format.
You may gather therefore that SpartaDOS is a commercial product that costs
money, whereas MyDOS is Freeware and available from your favourite Atari8
Bulletin Board or PD library. A fluency with your chosen DOS is necessary as
obviously they will be pushed to their limit when the larger capacity drives are
chosen.
SpartaDOS
The advantages of SpartaDOS are realised when operating at larger capacities.
Normally only 64 files or directories are allowed within any directory of MyDOS.
SpartaDOS 3.2 supports twice this amount, and much more with SpartaDOS X. The
limitation is very easy to forget especially with MyDOS and is very annoying
when you get the error informing you of a full directory! SpartaDOS 3.2 does not
support D9: however, so if you need eight drives plus a computer RAMdisk it
cannot be done. A physical or emulated drive must be dropped in it's favour.
Time/date stamping is also supported and the author has included a program which
downloads the PC's time setting to the Atari, as these are normally battery
backed and quite accurate. A substitute for the ICD R-time8 cartridge.
Many custom command files have been written for SpartaDOS which facilitate
directory sorting, testing of file structure integrity, and hard drive software
backup, although this is probably better achieved using a PC backup method!
SpartaDOS versions higher than 1.x do not run on pre XL/XE machines however so
DOS selection is limited for older 400/800 machines and some replacement
operating systems on the XL/XE. Notably ones that attempt to emulate the 400/800
OS!
Speed & Capacity
Eight disk drives are supported from within HDEMUL and each can be loaded with a
16Megabyte disk image so capacity is no problem in this department. Bear in mind
though, that these eight virtual drives are attached to the SIO the same as any
other serial device for the Atari8 and operate at the normal speed of 19200 bits
per second via a set of logic gates and are not blindingly fast. 19200 bps is a
normal dial-up modem speed these days and is considered slow for drive to
computer communication. T