Disk performance and capacity

Affecting disk performance

• transfer rate
• seek time
• rotational latency
• Other neglected factors , Such as ： External data rate 、 Command overhead 、 Visit time, etc .

 

Disk capacity

• Cylinder-head-sector(CHS)
• ATA Specification (65536 C, 16H, 255S)

65536 cylinders x

16 heads x

255 sectors/track x

512 bytes/sector

----------------------

= ~137 GB

• BIOS limit (1024 C, 256H, 63S)

1024 cylinders x

256 heads x

63 sectors/track x

512 bytes/sector

----------------------

= ~8.5 GB

• Combined:

1024 cylinders x

16 heads x

63 sectors/track x

512 bytes/sector

----------------------

= ~512 MB

 

• Logical Block Addressing (LBA)

28-bit LBA in ATA-1: 2^28 * 512 = ~137 GB

48-bit LBA in ATA-6: 2^48 * 512 = ~144PB

MBR uses 32-bit sector numbers, so limits to 2^32 * 512 = ~2.1TB

GPT uses 64-bit sector numbers = ~9.4ZB

Reference material

https://zh.wikipedia.org/zh-cn/%E6%9F%B1%E9%9D%A2-%E7%A3%81%E5%A4%B4-%E6%89%87%E5%8C%BA