drew@wolf.UUCP (Drew Dean) (11/01/87)
My SE with Apple's 20Mb drive formatted out to 19,019K (as reported in the title
bar). For a supposedly 20Mb [formatted] drive, this is a lot of bad sectors.
I've seen other SE's down in the 17000K range. How big is the drive, and should
I be worried about the 1Mbyte I'm missing, or am I lucky to get 19,000K out?
Email replies and I'll summarize....
Drew Dean
Disclaimer: Any organization I may or may not be affiliated with may or may not
agree with my personal opinions, as expressed above....
UUCP: {ihnp4, sdcsvax}!jack!wolf!drew
This is my first posting to USENET, so I apologize if I messed anything up....raylau@dasys1.UUCP (Raymond Lau) (11/03/87)
In article <549@wolf.UUCP>, drew@wolf.UUCP (Drew Dean) writes: > My SE with Apple's 20Mb drive formatted out to 19,019K (as reported in the title > bar). For a supposedly 20Mb [formatted] drive, this is a lot of bad sectors. > I've seen other SE's down in the 17000K range. How big is the drive, and should > I be worried about the 1Mbyte I'm missing, or am I lucky to get 19,000K out? > Email replies and I'll summarize.... > HD Setup (since 1.3 I think) sets the HD to a fixed amount of usable space. Before, they formatted it to as much good sectors as that once existed, but that caused a minor problem. If you were to back up a nearly full hd, reformat it...and then find that there's less room...makes restoring that much more difficult! So Apple decided to leave a safety buffer and format it to a number in the 19Mb range... (expecting that there'll never be less usable space on the disk - unless the disk is in need of replacement)
tom@iconsys.UUCP (Tom Kimpton) (11/03/87)
In article <549@wolf.UUCP> drew@wolf.UUCP (Drew Dean) writes: >My SE with Apple's 20Mb drive formatted out to 19,019K (as reported in the title > bar). For a supposedly 20Mb [formatted] drive, this is a lot of bad sectors. I'm not sure about this, someone told me that disk drive manufacturers label their drives differently than you and I might think: a 20Mb drive is actually 20,000,000 bytes, NOT 20*1024*1024. Thus 20e6 bytes is 19.07 * 1024*1024 bytes. So.... if the routine used to put the size in the title bar does it this way then you're doing pretty well. I don't know about those other sizes, however. Anyone out there know better? -- Tom Kimpton {ihnp4,uunet}!iconsys!tom Icon International, Inc. {ihnp4,psivax}!nrcvax!nrc-ut!iconsys!tom Orem, Utah 84058 ARPANET: icon%byuadam.bitnet@wiscvm.wisc.edu (801) 225-6888 BITNET: icon%byuadam.bitnet
chow@batcomputer.tn.cornell.edu (Christopher Chow) (11/05/87)
||My SE with Apple's 20Mb drive formatted out to 19,019K. | I'm not sure about this, someone told me that disk drive manufacturers | label their drives differently than you and I might think: a 20Mb drive | is actually 20,000,000 bytes, NOT 20*1024*1024. Thus 20e6 bytes is | 19.07 * 1024*1024 bytes. So.... if the routine used to put the | size in the title bar does it this way then you're doing pretty well. Then again, it depends on the drive. I think my almost 1-yr old Dataframe 20 has 20110 k free when you reformat it. Christopher Chow /---------------------------------------------------------------------------\ | Internet: chow@tcgould.tn.cornell.edu (128.84.248.35 or 128.84.253.35) | | Usenet: ...{uw-beaver|ihnp4|decvax|vax135}!cornell!batcomputer!chow | | Bitnet: chow@crnlthry.bitnet | | Phone: 1-607-253-6699, USPS: 7122 N. Campus 7, Ithaca, NY 14853 | | Delphi: chow2 PAN: chow | \---------------------------------------------------------------------------/
jwhitnel@csi.UUCP (Jerry Whitnell) (11/06/87)
In article <2822@batcomputer.tn.cornell.edu> chow@tcgould.tn.cornell.edu (Christopher Chow) writes: |||My SE with Apple's 20Mb drive formatted out to 19,019K. || 19.07 * 1024*1024 bytes. So.... if the routine used to put the || size in the title bar does it this way then you're doing pretty well. | |Then again, it depends on the drive. I think my almost 1-yr old |Dataframe 20 has 20110 k free when you reformat it. | |Christopher Chow A short lesson on disk drive construction. A drive consists of a number (at least one, ususally more) of platters, each of which has two sides. These platters are stacked on a spindle, so that both sides are accessible. A drive also has a read/write head for each side of the platter, except that the top and bottom platters usually don't have any data on them, so no head. These heads can move back and forth on the disk surface. The disk will spin the platters, so each head can access the whole surface of the platter. If you hold the head in one place and spin the disk underneath it one rotation, the head will be able to see the circle on the platter's surface. This circle is called a track. There are a fixed number of tracks on each platter, with less then a 100 for floppies and going on up to several thousand for large hard disks. The number of tracks for similar size drives varies from manufacturo to manufactuor. Each track is further divided up into sectors of 512 bytes each (some use 1024, some other sizes). There is always a fixed number of sectors per track and a fixed number of tracks per head. So the maximum amount of space a drive will hold is given by the formula heads x tracks/head x sectors/tracks x bytes/sector. However, you may not see all of this space. All of the good drives will reserve some number of sectors or tracks to provide a place to map sectors that have bad spots in them. If the drive can't read a sector on the disk, rather then call the whole disk bad (which is a big waste of money :-)), it just puts the data in one of the reserved sectors and stores the information about where the sector was moved to in a map that it keeps on the drive. Since the number of reserved sectors is often decided by the formatting program, different versions of the program may give you more or less space for real use depending on which version you use. So for any 20 mbyte drive on the market, about the only thing you'll know is that you'll get more then 18 mbytes and less then 22 mbytes. Jerry Whitnell Lizzi Borden took an axe Communication Solutions, Inc. And plunged it deep into the VAX; Don't you envy people who Do all the things You want to do?