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- Newsgroups: comp.sys.mac.system
- Path: sparky!uunet!think.com!spool.mu.edu!umn.edu!csus.edu!netcom.com!drew
- From: drew@netcom.com (drew)
- Subject: Re: How many Bytes in a Kilobyte (The answer may surprise you.)
- Message-ID: <1992Dec12.224708.10026@netcom.com>
- Organization: Netcom - Online Communication Services (408 241-9760 guest)
- References: <1992Dec12.140350.1@tesla.njit.edu>
- Date: Sat, 12 Dec 1992 22:47:08 GMT
- Lines: 48
-
- there is no discrepancy, merely a misunderstanding. i presume this is
- explained in the mac reference manual.
-
- the finder's get info command reports two measure: the actual number
- of bytes used in the file (e.g., for one of my files, 78,040) and
- the number of KBs allocatted to the file on disk (for same file 77KB).
- the file system allocates blocks of fixed size (size of allocation blocks
- depends on size of disk, might be .5KB or 2KB, etc. This simply means that
- the total bytes allocated for this file (used up in disk space) is
- 77*1024 = 78,848, while the actual number of bytes within that space
- used by the file to store its information is 78,040.
- In general the difference between actual bytes used and bytes allocated
- by the fsys can be up to the allocation block size -1, and one would
- expect it, for random file distributions, to average at half the size
- of the allocation block. this wasted disk space is called internal
- fragmentation. the only way to recover it is to use smaller allocation
- blocks, with the disadvantage that more space is wasted in the fsys
- allocation tables...and more file fragmentation, and slower fsys access.
- you can manually split a larger disk into smaller ones (hard partitions)
- which will reduce the allocation size, with the disadvantages mentioned
- above, and the additional disadvantage that you will arbitrarily run
- out of space (in one partition) when there is space available (in other
- partitions). depending on your usage mode, such partitioning could
- actually be a benefit...but for most people, it's just a pain.
-
- -drew@netcom.com
-
- In article <1992Dec12.140350.1@tesla.njit.edu> erh0362@tesla.njit.edu (Elliotte Rusty Harold) writes:
- >
- > How many bytes are there in a kilobyte as reported by the Finder in 6.0.7?
- >Some simple tests revealed that my Finder thinks there are only about 1010
- >bytes per K. For instance my FAX Manager folder is 304,262 bytes. Finder's
- >Get Info reports that as 301K. Disk Doubler's Savings command also reports
- >that as 301K or about 1010 bytes per kilobyte. SpaceSaver's Magic Menu
- >correctly to my way of thinking reports that as 297K or 1024 bytes per kilobyte
- >(rounded down by about 0.1K.) Needless to say that different programs can't
- >agree on the number of bytes per kilobyte makes comparing the various file
- >compression utilities more difficult than it should be. I expect this
- >weaseling about bytes/K from hard disk manufacturers but not from the Finder!
- >Can anyone explain what's going on? Note that I have tried the obvious, i.e.
- >booting with extensions off and looking only at uncompressed files. The Finder
- >really seems to think there are only 1010 bytes in a kilobyte.
- >
- >Elliotte Rusty Harold Department of Mathematics
- >elharo@m.njit.edu New Jersey Institute of Technology
- >erh0362@tesla.njit.edu Newark, NJ 07102
-
-
-