Using disk drives
MZ-700 / MZ-800
Many computer enthusiasts talked in the 80's about disk drives in awed tones, which might led someone to think that they are something too complex for the average user to handle. In fact the awe was due almost entirely to the price, which was outside the budget of most home-users - or had been until recently, when German-made disk drives arrived on the scene ( imported to UK by Sharpsoft ) and much more reasonably priced than the previously available Sharp models. Also the availability of Sharps own MZ-1F11 sequential disk drive, which can be built into the MZ-700 / MZ-800 series. Today standard devices ( not the originals ) usable for MZ's are low cost drives but to get the interface card and the expansion box for the MZ-700 is a problem.
The concept of the disk drive is actually quite simple, particularly if we make comparisons with the world of hi-fi. Consider a favorite song which you have recorded on tape. You know that in recording, the sound is picked up by the microphone and translated by the recording head into magnetic pulses stored in the metallic coating on the tape. When you want to play your song back, you wind it forward to the appropriate place, and when you press PLAY, the magnetic pulses on the tape are read by the tape heads and fed through an amplifier to emerge from the loudspeaker as re-created sound.
Your computer data recorder works in exactly the same way, but instead of magnetic pulses reproducing musical sounds, it stores pulses representing the ones and zeros of binary codes. When you want to retrieve a program you wind the tape to the appropriate point and play it back, which loads the program into the computers memory. The real inconveniences with tape are that it is relatively slow - operating too fast would risk damage to the tape - and that you cannot go straight to a song ( or program ) in the middle of a tape; you have to wind sequentially through the tape until you reach the part you want.
If, however, your favorite song is on an LP record, you know that you
can lift the arm on your record-player and position it directly on to
the track you want to hear. You have random access to it ( no sequential
access like for the tape ). A disk drive works in a very similar way,
except that instead of using records, it uses a thin plastic disk, coated
with magnetic material similar to that on tapes. ( These disks are referred
to as floppy disks, partly because they can bend - though
I wouldnt recommend you trying it! - and partly so as to distinguish
them from the hard or Winchester disks which have a huge
capacity and which had their price to match: strictly for business use
! ) The disk is held in a thin card or plastic cover with a slot through
which the read-write head on the disk drive can access the magnetic
pulses on the surface of the disk - very like the arm of the record-player,
except that the read-write head does not actually touch the disk. Instead
it is held very close to the disk, at a distance where it can detect
the pulses stored there, while the disk revolves at very high speed.
With such fine tolerances it is necessary for the engineering of the
drive to be of the highest order, and this is what made them expensive.
Using disk drives with the MZ-700
The disk drive itself is a aluminum metal box measuring 360mm deep by 185mm wide by 87rnm high. The ribbon cable from the drive is plugged into the I/O port on the computer, as mentioned above. May be, the first models of the drives SFD700 / MFD700 had have other dimensions, capacities, and required their own power supply ? The power cable provided should be plugged into a convenient mains socket. I saw an advert which told me it has no power supply. My SFD700 and my MFD700 have an inbuilt power supply... However, take care not to cover the vents in the metal case while the drive is in use, as this could lead to overheating and possible damage.
In order to operate the disk drive, the computer needs some additional commands, and so a special BASIC incorporating these is supplied on disk. It is, in fact, fully compatible with your normal S-BASIC, ( so that your present stock of programs is not redundant ) and only takes up a little more of the computers memory leaving 31K ( 27K on later SUC version ) free for programs.
Having connected up the drive and turned on the power, you insert the disk containing the disk BASIC into the slot in the front of the drive and push it home. In appearance, the disk is actually a flat square of plastic, with a metal sliding cover to protect the read / write slot, and marked with an arrow on the top, to show you which way it should load into the drive. ( To eject disks, there is a press button next to the slot, but this must not be used while the drive is in operation. )
As you have just switched on the computer it is in Monitor mode, and now you type F followed by CR. The red pilot light turns on, to show that the drive is operating, and the BASIC then loads in 3 seconds, as opposed to the 3 minutes you have been used to with the data recorder !
This demonstrates very vividly the speed advantage of disk drives. The huge storage capacity means that you can have a lot of programs or data files on one disk, which can be accessed very quickly.
Along with the S-Disk-BASIC is provided a utility program which allows you to make back-up copies of disks, and, perhaps most important, transfer material from tape to disk. This means that you can store your existing taped programs on disk, where they are much more quickly available.
The MFD700 3.5 disk drive from K & P was specified in an advert as being single-sided double-density 40 track - this simply means that it uses only one side of the disk ( my MFD700 uses both sides.. ) which helped to keep down the cost of the drive and the rest of the description refers to the way in which data is stored on the surface of the disk, allowing 180K to be held in such a small area. The compact size of the unit, ease of connection and use, and above all, relatively low price, made it an ideal choice for the home user for whom cassette tapes were too slow or too restricted for data storage.
For the more ambitious hobbyist or small business user there was the larger 5.25 disk drive SFD700 with a capacity of 280K per disk. The version of S-Disk-BASIC which operates it is slightly larger, taking up some 37K of the computers memory. Installation and operating procedures are similar to those for the MFD700, but the main advantage of the 5.25 drive is that it can be used with CP/M. This stands for Control Program for Micros and is a common operating system used throughout the business world.
To use a Quick Disk drive MZ-1F11 at the MZ-700 please read the next
section too even it is written for MZ-800 owners.
Using disk drives with the MZ-800
The MZ-700 doesn't have a cabinet unit like the MZ-800 has, so a connection by a cable from the I/O bus connector of the MZ-700 to the expansion unit is required. All interfaces from Sharp, K & P, and others are to be installed into the expansion unit if using them for the MZ-700.
The Quick Disk, together with the appropriate interface ( MZ-800: MZ-1E19, MZ-700: MZ-1E14 ) and a box of the special 64K per side disks, had cost rather less than the price of the computer, while the single floppy 320K disk drive had cost as much as the basic computer and the interface for it added nearly half as much again. The dual disk drive with interface had cost over twice as much as the computer. For the home user the dual disk drive represented a substantial investment, but for a business user it was possible to set up a complete system for under one thousand pounds.
We shall now examine the options in more detail, starting with the
most expensive and ending with a device which, while not strictly a
disk drive, allowed the hobbyist similar facilities at a very reasonable
Floppy disk drives ( MZ-1F19 single or MZ-1F02 dual )
The disk interface is fitted into a slot concealed by the largest metal cover at the rear of the MZ-800 computer above the volume control. The cover is released by removing two cross-headed screws, and then the disk interface simply slides into the slot, as indicated in Section 7.2.2 of the MZ-800 Owners Manual. As the interface projects out of the rear of the computer, it is a good idea to fit the optional cover ( MZ-1X17 ).
MZ-700 owner put the interface into an expansion unit e.g. MZ-1U06 which is to connect to the MZ-700's I/O bus connector.
The interface is connected by a cable to the drive(s). The drives are of vertical design and stand alongside ( not on ! ) the computer. When the computer is switched on, any disk in the drive will load automatically.
In the previous section we made reference to CP/M, which is one of
the major operating systems for business software. The MZ-800 offered
PCP/M - Personal CP/M - which is a far more user-friendly version of
CP/M. The PCP/M disk which was supplied contains a range of valuable
utility programs, and includes one which allows the user to control
the format of one of the drives so that you can read or write data which
is then compatible with other Sharp machines and even with the IBM PC
( although I cannot confirm this from personal experience ). Thus, the
floppy disk drives give the user access to a vast range of commercial
software and made the computer a practical proposition for the small
Quick Disk ( MZ-1F11 )
RAM file card ( MZ-1R12 / MZ-1R18 )
The RAM file cards fit into the expansion slot cabinet ( as illustrated in Section 7.2.3 of the MZ-800 Owners Manual ). Again, MZ-700 owners need an expansion unit for both MZ-1R12 or MZ-1R18. The MZ-1R18 provides 64K of memory ( MZ-1R12 32K ) which can be accessed as if it were a disk drive. The only snag for the MZ-1R18 is that, as with the main RAM memory, the contents are lost when the power is switched off. The MZ-1R12 has its own memo power and the RAM contents aren't lost. But the MZ-1R12 has 32K only, so you need two cards to get 64K. For the MZ-1R18: Consequently it is necessary to save the contents either to tape ( which will be a dow job ) or ( ideally ) to a Quick Disk. The penalty of having to back up the RAM file memory is however a small price to pay for the convenience of having rapid access to additional files or data.
BASIC MZ-1Z016 already contains the additional commands required to operate the RAM file card. The first is DIR which displays the names of the files currently held on the RAM file card. It is used in the form DIR RAM or, if you wish to list the files on paper, you can direct the information to the printer with DIR /P.
You will now appreciate why the MZ-800 has the facility to specify the device name in certain BASIC instructions. It is clearly necessary to tell the computer whether you are calling up a file from the data recorder ( CMT ) or RAM file card ( RAM ). There is, however, a command DEFAULT ( short form DEF. ) which effectively says to the computer that if the device name is omitted from a command, it should assume the device specified by the DEFAULT instruction.
The command INIT, which you have previously met, can also be used to initialize the RAM file card. On doing so, you can decide how much of the available memory should be used for the RAM file, and you can then allocate the remainder as a printer buffer. The MZ-800 Owners Manual explains clearly how you can also use this command to specify how the printer buffer is to be used.
When using disk drives, it is possible to delete files from the disk, or rename them by a simple command. You also have this facility with your RAM file card.
DELETE (short form D.) removes a specified file from the RAM file
RENAME ( short form RENA. ) renames a file. It is used in the form RENAME RAM: AFILE, ZFILE. ( With both of these commands, RAM can be omitted if this has previously been defined as the DEFAULT device. )
The commands WOPEN#, ROPEN#, CLOSE#, PRINT#, INPUT# all operate with the RAM file card as the operational device but there are two additional commands which can be used with this device. The first is the sadistic sounding KILL# ( short form KI.# ). This stops the writing of data into the file specified by the logical number following # but if you do not specify a logical number it stops all current data writing. It also closes the file(s) concerned and frees the logical number(s) for reuse.
The command EOF(F) ( short form - for what its worth - EO.(#)
) is used to find the end of a data file. Previously, when reading in
100 ROPEN#2, DATAFILE
You can also use the RUN command in the form RUN RAM: PROGRAM, which loads the file called PROGRAM from the RAM file card into the working RAM memory and then executes the program. SAVE and LOAD are used in the normal way, but with RAM specified as the device name, to transfer programs to and from the RAM file card.
In this section I have only given a brief review of the use of the RAM file card, as it is covered fairly thoroughly in the MZ-800 Owners Manual. I hope, however, it has sufficed to show you that having a RAM file card will make life much easier, and make more effective use of the time which you have to spend with your computer.
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