On Wed, Feb 19, 2003 at 10:16:57AM +0800, [K][R][Y][P][T][O][N] wrote: > Anyone can educate me about the difference of LBA, LARGE and NORMAL.
These distinctions came about because of the size limitations inherent in the BIOS disk handling. The original PC BIOS had a limitation of 1024 cylinders, 255 heads, and 63 sectors because of the way the registers were mapped in int13h calls. Since no real drive physically has more than 16 heads, that left you with a 537 MB limit (assuming 512 bytes per sector). This is what happens in NORMAL mode. LBA is logical block addressing, and uses a unique sector number so you don't have to fool around with drive geometry anymore. Trouble is, you still need a way to map LBA into a logical drive geometry for systems that still make use of the BIOS calls, such as LILO or (more importantly) the partition tables. This translation leaves you with a limit of 8.4 GB if you stick with the PC BIOS interface limits above (so you can have a logical 255 heads). The LARGE option is only supported by Award BIOSes, and is an older kludge that works in software, within the Award BIOS HDD service routines. It works by dividing the maximum physical cylinder number by 2 and at the same time multiplying the physical head number by two, so that you can have 1024 heads and 32 cylinders at most, leaving you with a 1 GB limit. Unless you have really old non-LBA software hanging around, don't use this option. > What are the advantage? See above. > Why do we have to choose from the 3? Legacy systems. Grr... > Does it affects the OS installed on it? Depends on whether the OS still feels the need to fool around with the BIOS instead of accessing the drive hardware directly. If you use Linux, none of this matters, because it will read the drive's size by sending direct commands to the IDE controller. Older versions of LILO required that kernel images be installed within the 1024 cylinder limit, because they used the BIOS to access the drive, so your choice would affect it. In NORMAL mode, you would need to have a /boot partition within the first 537 megs, LBA would require it to be within the first 8.4 gigs, and LARGE would require it to be within 1 GB. Other older OSes would simply fail to function if installed in a partition outside these limits. More information: Large Disk HOWTO: http://www.tldp.org/HOWTO/Large-Disk-HOWTO.html IDE HDD Mode Selection: http://www.nexcom.com.tw/4-tech_support/tech_info/ide.htm -- Rafael R. Sevilla <dido at imperium dot ph> +63(2)8123151 Software Developer, Imperium Technology Inc. +63(917)4458925 "Under the cloud of threatening war, it is humanity hanging from a cross of iron." _ Philippine Linux Users Group. Web site and archives at http://plug.linux.org.ph To leave: send "unsubscribe" in the body to [EMAIL PROTECTED] Fully Searchable Archives With Friendly Web Interface at http://marc.free.net.ph To subscribe to the Linux Newbies' List: send "subscribe" in the body to [EMAIL PROTECTED]
