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HDD 4: BIOS and Normal, CHS, LBA modes

BIOS

IDE Auto Detection - AWARD BIOS - MB K7T Turbo-R

Standard CMOS Setup - AWARD BIOS - MB K7T Turbo-R

Disk configuration - AWARD BIOS and MB ASUS CU2L

• When you are adding new hard disks connected through the EIDE interface you have to say to your computer how big the installed disk is. This you have to do in the BIOS system, where you can use several ways to accomplish it:

• 1. IDE Auto Detection from the main BIOS menu - Often used way for less experienced users and in case there are no portable disks using. The detection of the disk is carried out and the constant values are written into the CMOS memory. Then, when you start the computer again, the detection will not be used and the start will be faster. If you use portable disks you would rather change the settings to Auto in the Main menu.

• 2. Auto for disk settings in the Main menu - Often used way of configuration. The disk will be detected at each start of Windows. Recommended option in case of using different disks and portable disks. 

• 3. Manual configuration of parameters - this is only used in old disks having the capacity lesser then 1GB, on the newer disks the parameters are not given. 

• 4. Selection of the disk type - only in very old disks, newly the actual type of the disk is used. 

Int13h

• Interrupt 13h - Software interface of the BIOS system providing the access to the hard disk. The problem is in the limitation of the constant CHS values to 1023 x 255 x 63 and in the limitation of the capacity to 8GB.

• Interrupt 13h Extensions - BIOS with advanced functions int13h ext. - designed for exceeding the 8GB barrier and keeping the compatibility with older disks and OS. LBA instead CHS recommended. The demand on constant values determining number of C, H and S removed (here is no limitation to 1023 sectors)

Related settings of the BIOS system

• IDE HDD Block Mode (Multi-Sectors) - mode in which it is possible to transfer more sectors (block) in one time cycle. Using this mode in older computers and OS could cause some problems. In some BIOS systems also the number of blocks can be specified (from 2 to 32).

• IDE primary Master PIO (or PIO Mode) - possible to specify the PIO mode for a given device. 

• IDE primary Master UDMA (or Ultra DMA Mode) - possible to specify the UDMA mode for a given device. 

• On-Chip Primary PCI IDE - possible to switch off the controller.

• Delay IDE Initial - support for older disks that need much time for the initialization. The detection of the disks will be moved of the time you have chosen (from 0 to 15s).

• ATA RAID IDE Controller - option for motherboards containing another ATA /RAID controller. Turning the controller on and off (in case it is not used the start is of several seconds faster). For this setup, some motherboards use a jumper. 

• First Boot Devices - option for selecting the first device from which the OS shall be started. Here you can choose FDD, CD, ZIP, LS120, IDE0, IDE1.., ATA-RAID, SCSI... The most often used option is IDE0. In case of the other options, e. g. FDD, first the FDD drive is searched and then the remaining devices. Then, the start of the system is up to several seconds faster. 

• SMART Monitoring - switching the S.M.A.R.T. function on and off. 

• In older computers and BIOS systems you can find other settings, e. g. enabling LBA support for older controllers, low-level formatting, medium surface analysis (formatting and analyzing cause data loss).

Disk settings and the Access Mode (Translation Method)

• Drive Type - Each BIOS usually recognizes c. 47 standard pre-selected disks where each type has different preset parameters according to CHS. Recognizing disks by pre-selected types was used in first computers (there could appear some problems with different versions and types of the BIOS system). At present, in some computers they are not mentioned and the most frequently used setup is the automatic detection. Example of other types: None, Auto (automatic detection), User Type HDD (user parameters options), CD-ROM, LS-120, ZIP, MO, Other ATAPI Devices. 

• CHS (Cylinder-Head-Sector) (Normal) - Older method of defining the disk size by help of manual entering of number of cylinders, heads and sectors. At present, this method is not used and the LBA method is used most frequently. Designed for disks lesser than 504MB.

• LBA (logical block address) - using of linear sector addressing. The LBA was first designed to exceed the limitation of 504MB and to reach the capacity of 8GB. With the coming Int13h Ext. it starts to support the newest capacities. Instead of the classical CHS addressing, the 28-bit addressing of particular sectors is used. So, according to the ATA specification the BIOS can address sectors in the order from 0 to 268435455. 

• Large (Extended CHS) - other way of sector addressing. This is the recommended option in case you have some problems with the LBA support under your operating system. Standard mode for SCSI disks where the CHS configuration is not used. >From the view of the OS the CHS is translated to LBA.

• Auto - Automatic setup of the access mode (usually LBA).

• Match Partition Table - This option is rarely known, but you can meet it e. g. on the MBs by ASUS where the option is chosen according to the installed system on the disk. 

• Example of disks detecting under LBA:

• WDC 40GB - 19158 C x 16 H x 255 S

• WDC 30GB - 58168 C x 16 H x 63 S

• When you have entered incorrect information or the detection has gone wrong the disk will not work properly and you can also lose the data access!

Capacity limitation

• Overcoming of most limitations means no problem in newer systems, though, you can encounter such problems in some computers - then it is necessary to know how to cope with them. 

8,4 Gbytes - 16,383 x 16 x 63 x 512 bytes per sector = 8,455,200,768 bytes

• 504MB - limitation where the system is limited by the compatibility with the values of the BIOS system and the ATA interface by help of using the CHS mode. This limitation is valid for older computers 286/386/486.  (1024 cyl 16 heads x 63sectors/track x 512 = 528,482,304bytes  - 504 MB). In many cases special programs will help (Disk Ontrack Manager - Seagate, Disk Wizard - WD). Some operating systems can have problems with this software support and can have higher requirements on your knowledge of the OS and used programs.

• 2GB - Limitation of the maximal value of the FAT16 file system partition for DOS and Windows 9x. Some older computers cannot address more than 4095 cylinders (4,095 x 16 x 63x 512 - 2,113,413,120 bytes)

• 4GB Limitation of Windows NT - Partition with the FAT16 system cannot be higher than 4GB - Fdisk cannot be used for creating, but the Disk manager is used (Disk management in Windows 2000)

• 8GB - Limitation of the BIOS system. For the support of larger capacities you need extended functions of the BIOS system. Limitations valid for the x86 computers and some motherboards with Pentium and Pentium II processors. Some other operating systems must know how to use the extended BIOS functions (Extended Interrupt 13). We can use Windows NT 4.0 as an example where you need an updated disk driver or the Service Pack. (OS  - DOS 6.xx and lower, Windows 3.x and lower and some other older OS do not have the support of the Ext. Int13).

• 8 GB - Limitation of the FDISK program in the DOS 6.22 OS. 

• ?? GB - Possible problem with disks larger than 67GB under Windows 9x... See article WD800

• 32GB - (65535 x 16 x 63 x 512 - 33,822,351,360 bytes) other limitation of the BIOS system. 

• 68GB - Possible problem with disks larger than 67GB under Windows 9x... See article WD800

• 137GB - Limit for the ATA specifications (28-bit addressing for particular sectors - 268435455 sectors - 137,438,952,960 bytes)

• 2,2 TBytes - 32-bit addressing used by new operating systems (in Windows 98 by help of the FAT32 file system).

• 144 PetaBytes - a limit for new ATA specification using 48-bit addressing, in peparation. Maxtor, Microsoft, VIA, Compaq and other companies under name Big Drives participate the development. The standard should be implemented and authorized by the ANSI NCITS T13 Technical Committee organization (www.t13.org) in the prepared ATA/ATAPI-6 standard (see www.maxtor.com/bigdrive)

Troubleshooting the capacity limitations of 528MB - 8GB

• Using of a more recent disk controller with the LBA support.

• BIOS system update.

• For capacities over 8GB you also need the OS support 

• To exceed the limit of 528MB or 8GB you can use special SW tools (Disk Ontrack Manager - Seagate, Disk Wizard - WD (EZ-Install)).

Troubleshooting 32GB

• Using of a more recent disk controller.

• BIOS system update.

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