Re: structure of the disks themselves
Because of this a high density disk which is theoratically two megabytes comes up as merely 1.44 megabytes. There is a certain amount of material wasted. Hmmm? Isn't this because of data redundancy that prevents data loss in case of trouble? (think stuff like parity control, checksums, etc.) Marcin Wichary e:\ [EMAIL PROTECTED] w:\ www.aci.com.pl/mwichary Attached w:\ www.aci.com.pl/mwichary/gui Graphical User Interface gallery w:\ www.10yearsofbeingboring.com 10 years of Being Boring w:\ www.usability.pl Usability.pl -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
Re: structure of the disks themselves
Because of this a high density disk which is theoratically two megabytes comes up as merely 1.44 megabytes. There is a certain amount of material wasted. Hmmm? Isn't this because of data redundancy that prevents data loss in case of trouble? (think stuff like parity control, checksums, etc.) It's because of sector formatting. Here's a section of track, full of 1s and 0s: 10101010101010101010101010101010101010101010101010101010101010101010 Here's the end of a sector and the beginning of the next: 010101010101011101010110 First, part of that data is the sector header, which uses up a bit of space. Second, part of that data is not data... Those Xes are unused potential bits. Why? because the next time you write a sector the timing may be slightly different and it may end up looking like this: 10101010010101010101011101010110 If the previous sector had started right after it, you'd have just overwritten the sector header and destroyed the sector. On the Amiga, they wrote the entire track in one pass, so you only had to put the inter-sector gap at the end of the track. That gave you 1760K on a 2Mo flippy. You could also drop most of the sector headers by modifying AmigaDOS and get 1920K in a 2Mo floppy, so long as you didn't care that you could only read it on a similarly modified AmigaDOS. -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
Re: structure of the disks themselves
Hi all, Excellent explanation, Peter! Please let me add on more bit of information: since many concepts from Apple's MacOS came from Apple II's ProDOS, I'd recommend reading chapter 3 of the Beneath Apple ProDOS book, available at: ftp://ftp.a2central.com/pub/documents/beneathprodos.pdf If you take the time to read Chapter 3, you'll get a very good explanation of concepts like soft sectoring and physical formatting. Please consider that this book was written on a time where the common Apple format was the 140KB 5,25 floppy diskettes, but ProDOS itself was the first Apple OS to support the 400KB and 800KB 3,5 floppies. Although this is not Mac specific, I believe it's not too much off-topic because it applies to the concepts discussed herein. There is probably some good resources specific for the MacOS, also, which I'm not aware of. Regards, Celso. Peter da Silva escreveu: It's because of sector formatting. Here's a section of track, full of 1s and 0s: 10101010101010101010101010101010101010101010101010101010101010101010 Here's the end of a sector and the beginning of the next: 010101010101011101010110 First, part of that data is the sector header, which uses up a bit of space. Second, part of that data is not data... Those Xes are unused potential bits. Why? because the next time you write a sector the timing may be slightly different and it may end up looking like this: 10101010010101010101011101010110 If the previous sector had started right after it, you'd have just overwritten the sector header and destroyed the sector. On the Amiga, they wrote the entire track in one pass, so you only had to put the inter-sector gap at the end of the track. That gave you 1760K on a 2Mo flippy. You could also drop most of the sector headers by modifying AmigaDOS and get 1920K in a 2Mo floppy, so long as you didn't care that you could only read it on a similarly modified AmigaDOS. -- Celso Kopp Webber [EMAIL PROTECTED] (41) 7811-3858 (Nextel CD 55*47*428) (41) 9121-5188 (41) 284-3035 -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
Re: structure of the disks themselves
Peter da Silva wrote: It's because of sector formatting. Here's a section of track, full of 1s and 0s: 10101010101010101010101010101010101010101010101010101010101010101010 Here's the end of a sector and the beginning of the next: 010101010101011101010110 First, part of that data is the sector header, which uses up a bit of space. Second, part of that data is not data... Those Xes are unused potential bits. Why? because the next time you write a sector the timing may be slightly different and it may end up looking like this: 10101010010101010101011101010110 If the previous sector had started right after it, you'd have just overwritten the sector header and destroyed the sector. On the Amiga, they wrote the entire track in one pass, so you only had to put the inter-sector gap at the end of the track. That gave you 1760K on a 2Mo flippy. You could also drop most of the sector headers by modifying AmigaDOS and get 1920K in a 2Mo floppy, so long as you didn't care that you could only read it on a similarly modified AmigaDOS. Ahh, a Amiga user, maybe well should tell them how the Amiga uses a 880k disk format with its standard internel drive, how you can use custom drivers to increase this to 960k all on the same DD floppy that you could format as a MacOS 400 or 800k or a pc's 720k. The bulk of my disks for Amiga are formatted HD floppies with a 0.3% failure rate after 9 years not 9 minutes. Its a DD drive. My 1200 is a tad older than yours? The Macs drive is the problem not the media, they just weren't made for HD disks. While the auto inject/eject is a novel feature for mac removable media it can be a pain if you want that media inserted and available for manipulation as the wonderful OS insists on spitting out anything it doesnt understand unless you format. Sharing pc disks on a mac is also marvalous as the mac insists on adding is system file rubbish (invisable) to any non write protected media, marvelous for shares dished out from a non macos machine. Just alittle off the point. ;) BeOS possibly has the best/easiest selection of formats available for use with FD or HDD, Nix does also but what a pain in comparision. http://home.earthlink.net/~gamba2/system6.html#800 you may still find a usable link here for 800k disks and you live in the US -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
Re: structure of the disks themselves
On the Amiga, they wrote the entire track in one pass, so you only had to put the inter-sector gap at the end of the track. That gave you 1760K on a 2Mo flippy. You could also drop most of the sector headers by modifying AmigaDOS and get 1920K in a 2Mo floppy, so long as you didn't care that you could only read it on a similarly modified AmigaDOS. Ahh, a Amiga user, maybe well should tell them how the Amiga uses a 880k disk format with its standard internel drive, I thought I just did. :) 880 n 1Mo gives you 1760 in 2 Mo, and 960 in 1 Mo gets you 1920 in 2 Mo. My 1200 is a tad older than yours? I don't have one any more, but I had a low-serial-number A1000, not the first production run (it had EHB mode) but pretty early. My 2 Mo drive was an external. -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
Re: structure of the disks themselves
Peter da Silva wrote: On the Amiga, they wrote the entire track in one pass, so you only had to put the inter-sector gap at the end of the track. That gave you 1760K on a 2Mo flippy. You could also drop most of the sector headers by modifying AmigaDOS and get 1920K in a 2Mo floppy, so long as you didn't care that you could only read it on a similarly modified AmigaDOS. Ahh, a Amiga user, maybe well should tell them how the Amiga uses a 880k disk format with its standard internel drive, I thought I just did. :) 880 n 1Mo gives you 1760 in 2 Mo, and 960 in 1 Mo gets you 1920 in 2 Mo. My math is as poor as my spelling, I thought as my Amigas have no (lets call them 1.44) HD drives that breaking it down to something close to 800k would help with this thread. My 1200 is a tad older than yours? I don't have one any more, but I had a low-serial-number A1000, not the first production run (it had EHB mode) but pretty early. My 2 Mo drive was an external. Catweasle? I've never owned a1000 but believe the a4000 (they sold the toaster new up to a couple of years ago) has a 1.44 as its internal. -- Compact Macs is sponsored by http://lowendmac.com/. Support Low End Mac http://lowendmac.com/lists/support.html Compact Macs list info: http://lowendmac.com/lists/compact.shtml -- AOL users, remove mailto:; Send list messages to: mailto:compact.macs@mail.maclaunch.com To unsubscribe, email: mailto:[EMAIL PROTECTED] For digest mode, email: mailto:[EMAIL PROTECTED] Subscription questions: mailto:[EMAIL PROTECTED] Archive:http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/ --- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---
