SYSTEM SWITCH

THE NEW Kempston disc interface, a development of the Watford SPDOS, is one of the fastest interfaces we have seen for the Spectrum and it has some useful features.

Reliability proved to be a problem as the interface refused to work with either our own drives - used on all other Spectrum disc interfaces - or the Opus drive. That problem was eventually identified after trying three interfaces, and subsequent units should not suffer the same fate. If possible, either check with your own drive or buy the combined interface/disc drive package from Kempston. The interface was subjected to one of the longest tests we have ever given and it passed with flying colours.

At its simplest level, you can use the interface as you would a tape deck, to load or save a Basic program, Code or Data. You use the same commands as you would for tape but precede them by PRINT £4.

One useful byproduct of the system is that you can open channel three to a file on the disc. That means as this channel normally points to the ZX Printer, you can LPRINT to the disc and then later print out the file.

As well as Format, to initialise the disc, the usual Cat (display what is on the disc), Erase (delete a file from the disc) and Move (a file from one disc to another) are provided. They allow the use of wild-cards.

The interface has a number of extensions to Sinclair Basic. Clear can be used in two ways: Clear 0 will look through a Basic program and change all numbers to VAL "number", which saves three bytes per number. It also changes zero to NOT PI, one to SGN PI and three to INT PI which saves five bytes a time. On Tasword that saves about 1200 bytes, more than enough to offset the 703 bytes taken up by the interface.

The Kempston interface provides a fast and usable system. Provided Kempston can ensure the interface will work with a wide range of drives it should do well.

The interface alone costs £85, and a system including a 40-track drive is £185, both inclusive. It is not compatible with Interface 1.

Kempston MicroElectronics, Singer Way, Kempston, Bedfordshire MK42 7AW. Tel: 0234-856633.

THE EXPRESS GANG PART 3

Following the excellent Rotronics Wafadrive, and the Beta Plus (TR-DOS V4) interface of last issue, here's a look at two further units, the Kempston Disc Interface and the Opus Discovery 1. The Kempston belongs to the Shugart compatible interfaces and can run with any Shugart standard 3", 3.5" or 5.25" disk drive which incorporate a power supply unit. The drives must however, be capable of double density recording. The K-DOS operating system displays itself as an extended BASIC, where commands have to be called up via a PRINT #4 command. This proves to be laborious and a lot more effort is required when comparing with the simple Beta operating commands or even the Rotronics and Microdrive extended commands. A nice feature for BASIC programmers is the BASIC OVERLAY facility using the excellent MERGE with autorun, and the line definable CLEAR functions. The Kempston unit must be the smallest disk interface for the Spectrum, but this isn't necessarily a plus, as there is no extension port for other peripherals.

The Opus Discovery 1 is probably the most comprehensive add-on for the Spectrum next to the Timex drive. It incorporates a 3.5" disk drive, a parallel printer interface, a Kempston compatible joystick interface and a monitor output port and provides an expansion port for any further peripherals. The Opus Discovery 1 comes as a fully integrated unit, into which the Spectrum 48K or Spectrum Plus plugs. Provision is made to incorporate a second drive, but for this the unit has to be returned to the factory. The operating system is similar to the microdrive extended BASIC and the various ports for printer and joystick are accessed via separate streams. The Opus Discovery 1 is the ideal unit for users who abhor a multitude of separate enclosures and cables littering their precious desk space.

The next issue will feature the Timex disk drive and a complete comparison table featuring all the fast storage devices looked at in this series will summarise the various findings.

HARDWARE:

The Kempston disc interface must be the smallest unit of the series, measuring only 100 x 67mm. It has no expansion port and must therefore be connected as last in the chain of addons. Up to four disc drives (40 or 80 track, single or double sided) may be connected via a Shugart compatible 34-way IDC cable. To save space or cost the 34-way plug is not polarised, which means a trial and error connection. No harm can be done, as the Shugart pin layout only uses one side of the connector. A power indicator and a reset button are incorporated in the unit.

SYSTEM DESCRIPTION:

On powering up the system, the Spectrum will display the copyright message to indicate the presence of the Kempston DOS. This K-DOS can be included on the same line as BASIC statements, but care should be taken with standard PRINT statements, as these must be separated by use of a double colon to distinguish them from the parameter passing PRINT statements.

SYSTEM DESCRIPTION:

On powering up the system, the Spectrum will display the copyright message to indicate the presence of the Kempston DOS. This K-DOS is an extension of the Sinclair BASIC and is implemented via a software switch triggered by a PRINT 4 command. Parameters are passed on via a further PRINT statement. K-DOS can be included on the same line as BASIC statements, but care should be taken with standard PRINT statements, as these must be separated by use of a double colon to distinguish them from the parameter passing PRINT statements.

OPERATING SYSTEM:

Kempston DOS Version 2.0

SYSTEM COMMANDS:

All commands with the exception of INPUT#, PRINT# and INKEY$# are preceded by PRINT # 4:

CAT: PRINT d gives a catalogue of all files of drive d (1-4).

CAT:PRINT d, "string" gives a catalogue of all files on drive d, whose name contains "string".

CLEAR:PRINT m1, m2 deletes a block of BASIC lines starting at m1 and ending with m2.

COPY:PRINT d is a tape to disc transfer utility which allows the transfer of post unprotected cassette programs to disc. The command batch processes the tape files until a BREAK is detected. The tape must be stopped on a command prompt to allow block storage to disc. On saving, the command displays the filename, the start address and the length of file in decimal notation. Headerless blocks are saved using a "default n" filename. A break into the BASIC loader allows the modification of LOAD, SAVE and MERGE to K-DOS syntax. The transfer of tape programs obviously requires some knowledge of BASIC and possibly machine code.

ERASE "filename" erases "filename" from the directory of the current drive. The UP ARROW acts as a WILD CARD character.

ERASE "filename":PRINT d erases "filename" from the directory on drive d

FORMAT "diskname":PRINT i,j,k,l formats a disc on drive i (1-4) with j tracks (35, 40 or 80), k sides (1 or 2) and stepping rate (6, 12, 20 or 30ms delay).

GOTO m forces a BASIC program to jump to line m on any error (Error trapping).

INKEY$ # n reads the next character of a sequential file opened to stream n (n can be 0 to 15 with the exclusion of 4)

INPUT #n; var1; var2; reads the next record of a sequential file opened to stream n.

LOAD "filename" file type: PRINT d loads a program from the specified drive. The drive specifier is optional. The filetype may be CODE, SCREEN$, DATA a(), DATA a$() etc. Programs will AUTO-BOOT after a reset or power on if they are saved as file "AUTO" with a line number.

MERGE "filename":PRINT d loads a BASIC file from the specified drive and merges it with the program currently in memory. This function provides the use of BASIC overlays to reduce the memory requirement of large BASIC programs by autorunning from the line number specified in the SAVE function after having been merged in the main program residing in RAM. K-DOS's CLEAR acts as a block delete to prevent the execution of lines from the previous program.

MOVE "filel","fi1e2":PRINT d1,d2 copies files from a specified drive to another specified drive. It can also rename files or discs on the specified drive (Back-up on same disc). For single drive users d1 equals d2 and prompts for disc change are displayed automatically. If filename2 is a nullstring, then a copy with the same name as the source file (filename1) is created. Block copy is performed if filename1 is the nullstring. This option allows the back-up of a complete disc to be made. With filename1 a nullstring and a specified filename2 any files on the specified drive with the substring filename2 will be copied to the specified drive. This is useful for file extension systems (MOVE"", "/BAS";PRINT d1,d2 copies all files on drivel with the extension /BAS to drive 2).

NEW is similar to BASIC NEW with the exception that K-DOS remains enabled (K-DOS variables are not cleared).

OPEN#n,"filename":PRINT d opens a stream n to a sequential file "filename" of the specified drive d and assigns a buffer to it. If the file already exists, it is opened for reading, otherwise for writing.

PRINT# n; var1' var2' writes records var1, var2 etc. into buffer n for transfer to a sequential file.

SAVE "filename" LINE m :PRINT d saves the BASIC program "filename" onto the specified drive d. The drive specification can be omitted if it is the current drive. The optional line number will provide autorun from the specified line. If the filename is "AUTO" the program will autoboot when loaded.

SAVE "filename" file type: PRINT d saves CODE, SCREEN$, DATA a(), DATA a$() etc.

ERROR REPORTS:
27 error reports

EXTRA FACILITIES:
None

MANUAL:

24 page manual with introduction, installation, explanation of disc interface commands, error messages and K-DOS summary.

APPLICATION PROGRAMS:
None

CRITICISM:

Slow access times.
Complicated command structure with PRINT#4 calls.
Complicated handling of variables with the use of PRINT statements.
No machine code access to the DOS commands due to lack of information.

COMMENTS:
Average disc interface with good CLEAR and MERGE commands enabling simple BASIC OVERLAY system configuration.

MEDIA:
Depends on drives connected.

TECHNICAL SPECIFICATIONS:

Number of drives supported per system: 4
Storage capacity depending on drives connected.

PRICE:
£85 including VAT