What is the limiting factor that prevents older PCs from using a hard drive larger than 2.2 terabytes?

What is the limiting factor that prevents older PCs from using a hard drive larger than 2.2 terabytes?

• GPT (GUID Partition Table)
• MBR (Master Boot Record)
• RAM (Random Access Memory)
• UEFI (Unified EFI) 

 

EXPLANATION

This limit arises from the maximum size of the master boot record (MBR) partitioning method used by most personal computers. BIOS systems with MBR disks use 32-bit values to describe the starting offset and length of a partition. Due to this size limit, MBR allows a maximum disk size of approximately 2.2 TB and a maximum of four primary partitions.
UEFI supports the GUID Partition Table (GPT), a more flexible partitioning scheme. GPT disks use 64-bit values to describe partitions, allowing larger partitions. GPT also fixes other issues related to MBR (data integrity, backup tables, maximum number of partitions, ...). Using 64-bit values, GPT can handle disks of up to 9.4 x 10^21 bytes or 9.4 zettabytes (ZB).

SOURCE

http://www.uefi.org/sites/default/files/resources/UEFI_Drive_Partition_Limits_Fact_Sheet.pdf