YUNOVA · Computer Organisation & Architecture
Module 13: Storage and buses
Secondary storage: HDD and SSD
Key points
- HDD access time = seek time + rotational latency + transfer time.
- Average rotational latency is half a rotation.
- SSDs have no moving parts, so random access is much faster than on HDDs.
RAID levels
Key points
- RAID 0 stripes data for speed but has no redundancy.
- RAID 1 mirrors data; RAID 5 uses distributed parity and survives one disk failure.
- RAID 6 keeps two parity blocks and survives two disk failures.
Bus arbitration and standards: PCIe and USB
Key points
- Bus arbitration decides which device controls the bus when several request it.
- Daisy chaining, polling and independent requests are common arbitration methods.
- PCIe uses point-to-point serial lanes; USB connects peripherals through a host controller.