![]() New 3.5" Basic Master disks
written by Maurice Hawes / SUC/UK
Source: SUC-magazine July 2002, Volume 22, Number 2, p. 4 - 5 |
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A long series of tests with these disks on my MZ-80K produced the same
results as before i.e. disks seemed to format and copy O.K., albeit
with seemingly minor hiccups which cause occasional retries;
but most of them later refused to boot up first time, and some would
not boot up at all. We tried various tricks, such as increasing the
number of retries allowed, but Completely frustrated, we decided to try some new 3.5" 1.44MB disks that I happened to have handy, also bought from Dixons in Weymouth. To our utter amazement the first disk out of the box formatted and copied with no signs of any problems, and re-booted consistently every time; and this remained the case after a large number of subsequent experiments with other disks from the same box. So we decided to stick to 3.5" 1.44MB disks, and from then on all our formatting, copying and re-booting problems disappeared. We then turned to other problems. Some disk routines were crashing out because the drive heads were not being given enough time to move back from very high tracks; and the QUICKCOPY routine was returning the drive heads to HOME before every read or write operation. The first problem was solved by inserting a delay; but unfortunately the second problem did not respond to the type of solution we had already used successfully on the MZ-80B, MZ-80A and MZ-700, and we reluctantly bad to admit defeat on this point. Nevertheless, we now had a version of SUPERCOPY which could format and copy reliable 3.5" disks for the MZ-80K, and all we had to do now was to decide how to utilise the extra storage space these disks provided. The MZ-80K disk System differs in many ways from the disk System used on later MZ-machines such as the MZ-80B, MZ-80A and MZ-700. In this context the most important differences are as shown in the following Table:
The effects of these MZ-80K parameters are discussed on the next page. |
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The Theoretical Capacity Limits of various Disks on the MZ-80K ( p. 5 ) |
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On the other hand, whatever the size of the disk, the FAT always contains 256 bytes, of which 4 are used for system info ( Vol. No. & Sectors Used ). So there are always 252 x 8 = 2016 bits available to map used sectors. Therefore the theoretical capacity of a 35- or 40-track disk can be fully utilised, because all the sectors can all be mapped in the FAT with plenty to spare. But the 2496 sectors on an 80-track disk cannot all be utilised because the FAT is limited to 2016 sectors. Theoretically it might be possible to increase the size of the FAT
to allow it to map all the sectors on a 3.5" disk; but this would
involve software changes that would make the new 3.5" disks incompatible
with the old 5.25" disks, and this was considered to be an impracticable
step at this stage. |
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Setting the Actual Capacity of the new 3.5 MZ-80K disks |
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SP-7082 also has to know the first prohibited Track No. This is held at $5304, and on these new disks this location is set to $81 ( 129 ); this ensures that any attempt to write to Track 129 gives a Disk Full error. Summarising all this information:
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The Capacities of the New 3.5" Disks expressed in Bytes |
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A 3.5" Master disk with no other files on it shows fewer than 2000 free sectors because the SP-7082 Disk Basic File occupies 160 sectors and these are mapped as occupied in the FAT. So if you do DIR on an empty 3.5" Basic Master Disk ( i.e. one from which all other files have been deleted ) the DIR display should consist only of the header VOL.MASTER ( S.1840 ), indicating 1840 free sectors, equivalent to 235,520 bytes. Both these figures are vast improvements over the original Sharp figures
for their 70-track 5.25" disks ( Slave 135,168; Empty Master Disk
114,688 ) and we therefore feel that the exercise has been very much
worth while. |