authorBitten by the 137 GB Barrier? Do you have a large, new hard drive that wan’t install or less than full capacity?
By Bob Schwartz

Do you have a new large hard drive larger than 137 GB or larger, and you can’t seem to get it installed with all of its advertised capacity? You may have come up against one of the periodic hard drive size barriers. And, yes, in most cases, you can do something about it.

We have had a series of these “disk size” barriers – 504 MEGAbytes, 2.048 GIGAbytes, 4.2 Gigabytes, 8.4 GIGAbytes, 32 GIGAbytes, 64 GIGAbytes, and now the 137 GIGA byte barrier. Some of these were due to limitations of the BIOS and some to the operating system.

Early on, 24 bits was set aside to encode the various drive parameters, such as the number of cylinders, heads, and sectors per track. This was OK for small MEGAbytes drives. Then, when we installed a drive, we entered into the BIOS (basic input/output system) the number of cylinders, heads, and sectors. The operating system (DOS or Windows, etc.) figured out where to put the data on the disk. There just aren’t enough bits for that now. The new method is the LBA or logical block address which addresses the data and lets the hard drive electronics establish where it is on the disk. For more information on LBA, see a future article on LBA.

While the hard drive control electronics has to “know” about its physical geometry, its cylinders, heads, and sectors, the operating system (e.g. Windows) really only “cares” about the logical order of the data. The drive electronics of all of the newer drives accept logical block numbers. Given this, the drive electronics translates (converts) the logical block information, the sector number, to the particular physical location on the disk.

The first LBA effort for hard drives, used a 28 bit binary word which had a capacity of 268,435,456 sectors of 512 bytes, or 137.4 GIGAbytes. Years ago, this seemed quite adequate.

As drives got larger, the 137.4 GB limit was exceeded and the specification had to be updated. The newer specification was changed to incorporate a 48 bit binary word to represent the data location. 48 bits is 20 bits larger than the original 28 bit value, which is roughly a million times larger or 144 PETAbytes or 144, 000,000 GIGAbytes.

Pretty soon we may run into another “size barrier” because our 32-bit windows operating systems cannot address more than 2 to the 31 – 2,147,483,648 – or 2.1 TERAbytes unless it has been properly updated. 1 TERAByte drives are already on the market.

Now that you understand how the problem has arisen, let’s look at what we can do to achieve full capacity. If these items are done in the order shown, included installation software by the drive manufacturer should proceed smoothly and work. Make sure the installation software relates to the drive you bought, or go to their website for the latest version.

Actions to take:

1. Update the BIOS (Basic Input Output System) for your computer. Observe the opening screen when you boot up your computer. Usually it will identify the version of your BIOS that is installed. If not, download SIW.exe from the internet. Use Google or similar to find it. It is free. This is SYSTEM INFORMATION for WINDOWS. When installed, this can be used to identify which version of your BIOS is installed.
2. Go to the manufacturer’s web site of your computer; e.g., Dell, Gateway, Hewlett Packard, etc., and look up the model of your computer, looking in particular for BIOS updates.
3. If you built your computer, go to the site of the motherboard manufacturer (SIW can tell you who it is) and look for BIOS updates.
4. If this fails, go to the site of BIOS manufacturer – Phoenix, American Megatrend, etc. – and look for BIOS updates.
5. Download the latest BIOS update and the instructions to “flash” your CMOS or BIOS. When you get the BIOS update, install it.
6. It is essential that the BIOS can handle 48 bit LBA for disks larger than 137 GIGAbytes as step one.
7. Update your operating system. Using Windows XP as an example, make sure that at least service pack #1 (SP1) has been installed. SP2 has been available for some time, includes the features of SP1, and is strongly recommended. If you haven’t yet, download and install it. It is essential that the operating system comprehends 48 bit LBA. This is step 2.
8. In XP, make sure EnableBigLba in the registry has been set. Download the Microsoft Knowledge Base article KB303013 and follow its instructions. There is a program on the web that can help you with this.
If your system hardware or software is older than a few years, the above may not apply. You may be able to find an ATA PCI controller card, where you bought your drive, that can provide the appropriate drive control. Make sure that the card will be compatible with your hardware and software. Read the warnings because the disk format used may not be compatible with and may not be able to be “read” if later on you want to move this drive and its contents to another computer.
9. Highly unlikely, but possible! Many large drives are equipped with “size reduction” jumpers. You do not want one of these installed! Normally, there is only 1 jumper to select MASTER, SLAVE, or CABLE SELECT. If you see a second jumper, check the manufacturer’s instructions CAREFULLY!
Note: You may be motivated not to do the above, and try to take the easy way out. If, for example, you have a 160 GB drive, you might feel that letting the system set it up as a 137 GB drive, would be enough and would be OK. It isn’t! If somehow, you get a a 48 bit LBA signal to locate data on a drive that was set up in your system for 28 bits, once you exceed the 28 bit capacity, the address will “wrap around” and overwrite data at the beginning of the drive. DON’T DO IT! (To illustrate, consider a 4 bit group which ranges from 0000 to 1111. Add 1 more bit to 1111 and you get 10000. However, let us assume that only the lowest 4 bits – 0000 – are read. So by ADDING 1 bit, you are back at the beginning). So data that would otherwise be above 137 Gb will overwrite the first part of your disk. DON’T TAKE THE EASY WAY OUT, DO IT THE RIGHT WAY!

Bob Schwartz is a HAL-PC member, retired EE, 14 patents, technical writer, active in civic affairs: President, Brays Bayou Association; Vice President, Marilyn Estates Civic Association; Correspondence Secretary with the Willow Waterhole Greenspace Conservancy. He can be contacted at