The free space on our computers’ hard disks is getting consumed at a tremendous rate in our never-ending search for higher quality. HD video, 15-megapixel photographs, lossless audio, high-resolution textures of latest games are the reasons why we don’t measure hard disk capacities in just gigabytes anymore. It doesn’t matter if a hard drive has a few gigabytes more or less now that we use the term terabyte to describe it.After a long period of exponential development hard disk drives have slowed their pace down in the last year and a half. Besides the obvious manufacturing difficulties, the problem is that moving beyond the 2-terabyte barrier is not as easy as it seems.One aspect of this problem is in the Master Boot Record, a table located at the beginning of a partitioned disk and designed for choosing a partition an OS is going to be booted from. The MBR wouldn’t be necessary if we all had but one partition on each of our hard disks. The computer’s BIOS would initialize the disk and pass execution to code contained at a certain address. But as we do have multiple partitions, we cannot do without the MBR. The BIOS loads the MBR which in its turn loads the OS located in one of the partitions described in the MBR. The problem is that the MBR was invented when HDDs used to have much smaller storage capacities than today (by the way, the alignment requirement for today’s HDDs with 4-kilobyte sectors goes back to that time, too). The MBR could originally address only 224 sectors. One sector being 512 bytes large, this equaled 8.4 gigabytes. And even this method required some tricks with CHS (cylinder-head-sector) addressing which involved presenting an HDD as a monster with as many as 255 heads. Some users may still remember that problem. Later on, the LBA addressing mechanism was introduced to replace CHS and expand the addressable space to 232 sectors. This is about 2.2 terabytes. Thus, the MBR cannot access sectors beyond 2.2 TB. No new partitions can begin there, which means that a single-partition disk can have a maximum storage capacity of 2 terabytes. As HDD makers hold that 2 terabytes means 2 trillion (1012) bytes rather than 241 (which is a bigger number) as operating systems think, today’s 2TB HDDs are free from that problem, but something had to be done about 3TB models.