area on disk after the MBR and before the partition start-point
The old 32KiB gap between MBR and first sector of file system is called DOS compatibility region or MBR gap, because DOS required that the partitions started at cylinder boundaries (and each cylinder had 64 sectors i.e. 64 sectors * 512 bytes/sector= 32KiB space).
Legacy GRUB (GRUB1) could've used it to install GRUB1 1.5-stage bootloader there: http://www.gnu.org/software/grub/manual/grub.html#BIOS-installation.
Additional links:
- http://www.pixelbeat.org/docs/disk/
- https://superuser.com/questions/107235/how-do-boot-sectors-and-multiple-drives-works/108152#108152
- http://www.dedoimedo.com/computers/grub.html
This is a performance optimization and not related to Linux at all, just to the hardware. Modern disks (so called "4K" disks) use physical sectors of 4096 byte instead of 512. You still can address single 512-byte sectors but that may severely impact performance if the partitions (or rather: file systems) are not aligned to 4K.
Start sector 64 would be enough for this requirement. The increase to 2048 seems to be preventive (e.g. allowing to put an UEFI boot partition there if the disk should be converted to GPT later).