Once you finish a track on a platter, you write to the same track on the next surface.
This is because damping time is very high for a track change

Archiving a file in NTFS, results in the file being moved into the inner tracks
OS is stored on the 0th (outermost) track

DDR-SDRAM - Double Data Rate Synchronous Dynamic RAM

RAM is syncronous with an external clock. Data arrives at fixed intervals
DRAM uses capacitors, which need to be periodically refreshed.

CPU cache is an example of SRAM.
SRAM uses transistors, and is more expensive. It does not need to be refreshed

DMA controller polls the IO device, and raises an interrupt when data is ready

HDD Sector size: 512 bytes
Block size: 4KiB = 4096 bytes