Differences between MS-DOS style Master Boot Record (MBR), the Apple Partition Map (APM), and the UEFI-style GUID Partition Table (GPT) are such:
MBR and APM limit the usable disk size to 2 TiB (a partition can neither start nor end beyond the 2 TiB limit). With GPT, the disk can be up to 8 ZiB.
MBR is limited to four partitions.
To get around the limit, one of the partitions is usually created as an "extended partition" which nestedly contains a series of "logical partitions". The most common scheme for this is an Extended Boot Record, though BSD systems often nest a BSD disklabel instead.
APM can grow up to 62 partitions; GPT can have at least 128.
MBR partitions have a 1-byte "type" code, which is too small to be useful (most operating systems use very generic type codes and just guess the rest). Windows NT also introduced a 4-byte "disk ID" for distinguishing between multiple disks of the same model.
APM uses textual "type identifiers" (32 ASCII bytes), e.g.
Apple_UFS. It also reserves 32 bytes for a descriptive partition name.
GPT, as its name tells, uses a 16-byte GUID for partition type, another GUID for identifying a specific partition (the partuuid), and yet another GUID for identifying the whole disk (similar in purpose to the MBR "disk ID"). It also reserves 72 bytes (UTF-16) for a partition label.
Intel-based Macs can only boot from GPT drives, while PowerPC-based Macs only support APM.
"Regular" IBM-compatible PCs can boot any disk as long as the 0th sector contains a valid BIOS bootloader and the
AA55h boot signature. This usually means MBR, but all GPT-partitioned disks have a "protective MBR" that satisfies this requirement.
PCs using UEFI are required support both GPT and MBR – again, as long as an UEFI-compatible bootloader is present. (UEFI keeps bootloaders in a FAT32 partition with specific type code.)
(Exceptions: Some specific BIOS versions reject the GPT "protective MBR" as invalid, due to bugs or misfeatures. Also, Windows will refuse to boot from a GPT disk on BIOS systems, or from a MBR disk on UEFI systems, due to reasons unknown.)
In BIOS systems, the initial boot loader is part of the MBR. There can only be one bootloader in the MBR, resulting in conflicts when installing dual-boot systems. Due to the x86 DOS origins of the MBR bootloader, code is specific to the x86 architecture.
On the other hand, UEFI uses a dedicated FAT32 partition for bootloaders (potentially multiple) and other EFI tools. The partition contents can be easily managed from any OS.
Technical bits and pieces
- There is only one MBR or APM per disk, both starting at sector 0. GPT keeps a backup copy near the end of the disk.
A more detailed info related to MBR and GPT: Windows and GPT FAQ