Basic parameters of hard disk

1. Capacity
As a data storage device for computer systems, capacity is the most important parameter of hard disks.
The capacity of hard disks is measured in megabytes (MB) or gigabytes (GB), 1GB=1024MB. However, hard disk manufacturers
usually use 1G=1000MB when marking the nominal capacity of hard disks. Therefore, the capacity we see in BIOS or when formatting the hard disk will be smaller than the nominal value of the manufacturer.
For users, the capacity of hard disks is like memory, which will never be too much. In addition to easier operation, the Windows operating system has also brought about the increasing expansion of file size and number. Some applications will easily consume hundreds of megabytes of hard disk space, and there is a trend of continuous increase. Therefore, it is wise to be ahead of time when purchasing hard disks. The current mainstream hard disk capacity is 10G and 15G, and large-capacity hard disks above 20G have also begun to become popular.
In fact, the larger the hard disk capacity, the cheaper the price per byte. For example, the price of Fireball 10G is 1,000 yuan, and the price per G byte
is 100 yuan; while the price of Fireball 15G is 1,160, and the price per G byte is less than 80 yuan.
The capacity index of the hard disk also includes the single-disk capacity of the hard disk. The so-called single-disk capacity refers to the capacity of a single disk of the hard disk. The larger the single-disk capacity,
the lower the unit cost and the shorter the average access time. At present, the single-disk capacity of most hard disks on the market is more than 6.4G, and the higher has reached 10G.

2. Rotational
speed Rotational speed (or spindle speed) refers to the number of revolutions per minute of the hard disk platter, measured in rpm.
The rotational speed of mainstream IDE hard disks on the market is generally 5200rpm or 5400rpm, while Seagate's "Grizzly" series and Maxtor reach 7200rpm, the fastest among IDE hard disks. As for hard disks with SCSI interfaces, they generally reach a rotational speed of 7200rpm, and some even reach 10000rpm.

3. Average Access Time
Average Access Time refers to the time required for the head to reach the target track position from the starting position and find the data sector to be read or written on the target track. Average
Access Time reflects the read and write speed of the hard disk. It includes the hard disk seek time and waiting time, that is: Average Access Time = Average Seek Time + Average Waiting Time.
The average seek time of the hard disk refers to the time required for the hard disk head to move to the specified track on the disk. Of course, the smaller this time is, the better. At present, the average seek time of hard disks is usually between 8ms and 12ms, while that of SCSI hard disks should be less than or equal to 8ms. The waiting time of the hard disk, also called latency, refers to the time when the head is already in the track to be accessed and waits for the sector to be accessed to rotate under the head. The average waiting time is half of the time required for the disk to rotate once, which should generally be less than 4ms.

4. Transmission rate

Data Transfer Rate The data transfer rate of a hard disk refers to the speed at which the hard disk reads and writes data, measured in megabytes per second
(MB/s). The hard disk data transfer rate includes the internal data transfer rate and the external data transfer rate. The internal transfer rate is also called the sustained transfer rate, which reflects the performance of the hard disk buffer when it is not in use. The internal transfer rate mainly depends on the rotation speed of the hard disk. The external transfer rate is also called the burst data transfer rate or interface transfer rate, which is the nominal data transfer rate between the system bus and the hard disk buffer. The external data transfer rate is related to the hard disk interface type and the size of the hard disk cache. Currently, the maximum external transfer rate of a Fast ATA interface hard disk is 16.6MB/s, while that of an Ultra ATA interface hard disk reaches 33.3MB/s.

5. Cache

Like the RAM Cache on the motherboard, the purpose of the hard disk cache is to solve
the problem of mismatched read and write speeds between the front and back ends of the system, so as to improve the read and write speeds of the hard disk. Currently, most IDE hard disk caches are between 128K and 256K, while Seagate's "Grizzly" series uses 512K Cache.