krieg@jupiter.uucp (Andrew Krieg) (10/24/89)
I have a few questions about disks and disk formatting for the ST. 1) I use Universal Item Selector II and it has an option for formatting disks. They offer a format scheme known as Twister format. What is this? Why would I want to use it? Can all drives read it? 2) I have both the Atari single-sided and double-sided drives. Both of these drives allow me to format up to 82 tracks, but they can't seem to read past the 80th track. Should this be? Why can it format out to 82 but only read up to 80? I'm confused. If I formatted with Twister, could I read up to the 82nd track? 3) Are there any 3rd party drives that support 1.4M disks? By suuport I don't mean that they will format them to 800K but to the full 1.4M mark. In conclusion, I'd like to state that I'm sick of all the TT/386/Apple bashing. Let's stick to ST information, etc. for a while. -- ========================================================================= = The Marvel Historian A. Krieg = = G.E. Medical Systems - CT - New Berlin, WI = = USENET: krieg@jupiter.med.ge.com = ========================================================================= = "Landing gear, landing gear, landing gear. = = Have a beer, shut the door." - Howard Borden = =========================================================================
woodside@ttidca.TTI.COM (George Woodside) (10/25/89)
In article <1295@mrsvr.UUCP> krieg@jupiter.uucp (Andrew Krieg) writes: >I have a few questions about disks and disk formatting for the ST. > > 1) I use Universal Item Selector II and it has an option for > formatting disks. They offer a format scheme known as Twister > format. What is this? Why would I want to use it? Can all > drives read it? "Twister" is a formatting technique developed by Dave Small and Dan Moore for STart magazine. It normally uses ten sectors per track, while the standard desktop format is nine sectors per track. That is OK for most disk applications, but be careful of disk-to-disk copies. They may not work correctly if both disks are ten sectors, and will certainly fail if only one is ten sectored (unless you are using a very smart copy utility). Other than that potential problem, all drives I've ever heard of can read and write ten sectors reliably. > > 2) I have both the Atari single-sided and double-sided drives. Both > of these drives allow me to format up to 82 tracks, but they can't > seem to read past the 80th track. Should this be? Why can it > format out to 82 but only read up to 80? I'm confused. If I > formatted with Twister, could I read up to the 82nd track? While some people believe in cramming every bit of data they can onto a disk, I don't. You're playing with fire, and will eventually get your just rewards. You may not really be getting 82 tracks formatted, the software may just think you are. The drives used in these machines are spec'ed to provide reliable service for 80 tracks. If the head stepper is capable of stepping beyond the proper range for one or two more tracks, that is a quirk, not a designed, reliable, or industry-wide standard feature. It may not be true of a drive mechanism used to replace the current one in event of a failure, or even of the same drive after servicing and alignment. In two drive systems, one drive may be able to reach 81, or 82 tracks, while the other may not. Formatters (generally speaking) write a track, then read it back to verify it has no errors. They can only tell that what they just wrote is valid. If your drive can step to 80 tracks, but not 81, the formatter acts this way: 1) Format and read back the first seventy nine tracks (while these are really tracks 0 - 78, we'll refer to them as 1-79 to keep the details understandable). 2) Step to track 80. Format it, read it back, and it reads OK. 3) Step again. The drive head may not be able to go in another full track. It may not have moved, may have moved part of the track width, or may have moved a full track width. The software doesn't know that anything may be in error. 4) Format and read back track 81. This will appear to be OK, since the drive lays down the track where it is currently positioned. That may have partially or completly obliterated track 80, or may not, depending upon the distance the head actually moved. 5) Do this again for track 82. Again, track 82 appears to be valid. It may have destroyed track 81, which may or may not have destroyed track 80. The upshot of al this is that the formatting software thinks it has written 82 valid tracks, while reality may be that you have 80, 81, or 82 valid tracks. The last track (82) will be valid, but 80 or 81 may have been corrupted in the process. That will result in write and read failures when the disk accesses those final tracks. To determine whether you really can step to 81 or 82 tracks, you'll need to fill the disk with data, then read back the last few files. I'd suggest you forget tracks 81 and 82. If you opt for ten sectors per track, just be careful of disk-to-disk copying. Now, one more thing that "Twister" pioneered - sector skewing. The original desktop formatter (and most 3rd party formatters) always wrote the sectors on a track in 1-9 or 1-10 sequence, starting with sector 1 (yes, sectors are numbered from 1, while heads and tracks are numbered from 0. Don't ask!) Dave and Dan figured out that after writing sector nine on one track, the drive stepped to the next one, waited a brief time to be sure it stopped moving, then started looking for sector 1 to read or write. But, it had passed by, so the drive had to wait one disk revolution for it to come by again. They figured out that the time required for the head step and settle was greater than the time it took to pass one sector, but less than two sectors. So, they "Twisted" the sectors on each track. If the sequence of sectors on track 0 is 1 2 3 4 5 6 7 8 9, then they put the next track (either head 1 of track 0, or head 0 of track 1, depending upon whether the drive is double sided) in the order 8 9 1 2 3 4 5 6 7. That way, just as the head is ready to start looking for sector 1, it comes along. ST's with ROMS prior to TOS 1.4 format all tracks in 1-9 order. Beginning with TOS 1.4, the sectors are "Twisted" in the same manner by the desktop formatter. The TOS 1.4 formatter also writes a boot sector compatible with MS-DOS, so you can interchange ST and IBM disks. Be careful, however, of formatting lots of disks on MS-DOS machines, and using them in STs. MS-DOS doesn't put serial numbers on disks, and the ST depends upon them to tell when disks have been changed. > 3) Are there any 3rd party drives that support 1.4M disks? By > suuport I don't mean that they will format them to 800K but to the > full 1.4M mark. None that I know of. 720K and 1.4M disks rotate at the same speed. To achieve the higher capacity, the rate at which data is transferred is doubled. This requires hardware modifications inside the ST. >In conclusion, I'd like to state that I'm sick of all the TT/386/Apple >bashing. Let's stick to ST information, etc. for a while. AMEN! -- *George R. Woodside - Citicorp/TTI - Santa Monica, CA *Path: ..!{philabs|csun|psivax}!ttidca!woodside
apratt@atari.UUCP (Allan Pratt) (10/26/89)
krieg@jupiter.uucp (Andrew Krieg) writes: >I have a few questions about disks and disk formatting for the ST. > 1) [What is Twister format?] > 2) [Why 82 tracks?] > 3) [Are there any 1.4M drives out there?] "Twisted" disks have sectors on successive tracks offset from one another. Instead of always starting sector 1 at the index mark, they start sector 1 there on track 0, sector 3 on track 1, sector 5 on track 2, and so on. This makes disk I/O faster, because there are only two sectors of latency between reading sector 9 from track 0 and sector 1 of track 1, instead of 9 sectors of latency waiting for the whole disk to spin around. You get "Twisted" disks any time you format a disk from the Desktop using Mega TOS or any newer TOS. Once the disk is formatted it will be fast no matter where you use it. Atari disk drives are only guaranteed to handle 80 tracks. Some people have discovered that some drives can actually access 82 tracks, so they have written formatters which will format 82 tracks. This is not recommended, and you can actually damage your disk drive by telling it to seek so far that it bangs into something. The Desktop format operation will only format 80 tracks. I am not aware of any 1.4M drives available for the ST. I know you couldn't just plug one in: they get 1.4M by doubling the data rate, and the controller inside the ST couldn't handle it. ============================================ Opinions expressed above do not necessarily -- Allan Pratt, Atari Corp. reflect those of Atari Corp. or anyone else. ...ames!atari!apratt