
And as you can see there there are various options on the format type and the name of course. The two main options are the
HFS (Mac OS extended) and FAT32. There two drastically different
formats developed by Apple and Microsoft respectively and they are different approaches in handling the different bits of the hard drive. There are 4 different variations of the the Mac OS Extended (case sensitive,
journaled and combinations thereof)
File Allocation Table or
FAT is a computer file systems architecture originally purchased by and then developed by Bill Gates and Marc McDonald during 1976/1977. It was used through the whole history of Microsoft (MS DOS, Windows) until the Windows Me. The structure of the FAT system is the division of the hardware space to sectors that contain specific number of bits and a number of bits to describe those sectors (12, 16 and 32). The system will
allocate a sector or sectors of the drive to each file. Now if since the Hard Drives are using the Binary system 0 and 1 the number of bits that
can be
allocated to one file is 2
32=42944967296Bytes=4GB. So there you have the number one issue with FAT32; the maximum file size cannot exceed the 4GB. However, the format is acceptable by any type of operating system
MacOS, Windows, Linux/Unix etc. Also one of the major benefits is the least data loss in case of hard drive failure. Since the the damage can affect the a sector or a neighboring group of sectors damages only the file that is
occupying them. One of the
disadvantages is the
fragmentation that occurs to the drive over the repeatedly erasing and writing. This can increase the seek time and can slow down the process. Although there are
de-fragmentation tools are not as effective.
Pros: Minimum data lose.
Cons: Maximum file size 4 GB,
fragmentation.
Hierarchical File System or
HFS was introduced by Apple in September 1985 specifically to support Apple's first hard disk drive for the Macintosh, replacing the Macintosh File System (
MFS), the original file system which had been introduced over a year and a half earlier with the first Macintosh computer. According to the
HFS the Hard Drive into logical blocks of 512 bytes. Those blocks can be then be allocated (allocation blocks) to various files. The
HSF uses 16 bit system to allocate those blocks in binary system so the number of different allocation blocks are 2
16=65,536. Therefore the limit of 65,535 allocation blocks resulted in files having a "minimum" size equivalent 1/65,535
th the size of the disk. So for a 1 GB disk, the allocation block size under
HFS is 16 KB, so even a 1 byte file would take up 16 KB of disk space. However, being
younger than FAT has a smarter way of handling the folders. It consists of 5 hierarchic blocks:
- Logical Block 0 and 1 that contain the information for the system start-up
- Block 2 contains the Master Directory Block (aka MDB). This defines a wide variety of data about the volume itself, for example date & time stamps for when the volume was created, the location of the other volume structures such as the Volume Bitmap or the size of logical structures such as allocation blocks.
- Logical block 3 is the starting block of the Volume Bitmap, which keeps track of which allocation blocks are in use and which are free.
- The Extent Overflow File is a B*-tree that contains extra extents that record which allocation blocks are allocated to which files, once the initial three extents in the Catalog File are used up.
- The Catalog File is another B*-tree that contains records for all the files and directories stored in the volume.
This architecture results in a more effective seeking and faster response and eliminates the need of de-
fragmentation. However since one block handles all the files it prevents multitasking and
further if the section of the hard drive that contains that information is damaged the hard drive is having a complete failure. To address this issue Apple introduced the
HFS Plus that fixed the multitasking but the catastrophic failure remains an issue. In the
MacOSX generation system these formats are known as the
Mac OS and
Mac OS Extended. Although they addressed all the mentioned issues, this file
management system is not compatible with any other operating systems.
In November 2002 Apple
introduced the
Journaling which allows the system to log the changes before they are executed. So although typically deleting a file involves to processes deleting the file entry and then marking the space it is
occupying as free, a power failure in any of the steps will results in abnormalities. For example, if the power failure occurs during the first and second step, the file will be erased without being deleted.
Journaling will first log those changes and then execute them marking them while it is done. That will ensure that both steps are executed properly and in the right order. With 10.3 it was
introduced the case sensitivity that discriminates Names for names or
NaMeS.
Pros: No file size limit, 255 characters to name the file and folders, case sensitive,
journaling.
Cons: Minimum file 16
kB, maximum file limit, lack of
cros-platform
compatibility, danger of
catastrophic data loss.
So when you buy a new drive, think before you start using it. If you plan to store videos that is more than 4 GB (only videos can be single files larger than 4
Gb) then go for Mac OS Extended, Case Sensitive, if you are planning cross platform
definitely use FAT32. Especially for the USB drives, since the added bonus that are RAM types of drives, has almost no seek time, regardless of fragmantation. Just keep in mind that the K=1024, M=1024x1024=1,048,576 and G=1,073,741,824 bites. So your 1 TB drive is 1,000,000,000,000 bits is actually 931 GB and not 1000 GB.