Computer hard disk basic knowledge Daquan

　　Computer hard disk is a very important part of the computer. Computers will not work if the computer's hard drive fails. Here to introduce the computer hard disk related knowledge:

The hard drive on the market is divided into two main categories: IDE and SCSI. SCSI hard disk has fast, large capacity, the use of stable features, is the vanguard of hard disk technology, but its price is too expensive, mainly for more professional occasions. While the IDE hard disk, although the technical level is still some of the gap with SCSI hard drives, but there is no doubt that the gap has become less and less, today's IDE hard disk also has a fast speed, large capacity characteristics, and its cheap, has become the first choice for home occasions.

The IDE's hard disk can be divided into 5.25, 3.5, 2.5, and 1.8-inch hard disks by the size of its internal disc diameter. 2.3 and 1.8 inch disc diameter hard disk is mainly used for laptops and other devices, 5.25 and 3.5 disc diameter hard disk is mainly used on the desktop, and now the most common desktop is the size of the 3.5-inch disk diameter hard drive.

1. The capacity of the hard disk

When we buy the hard drive, we ask first, how big is the hard drive? Answer: 40GB, 80GB, refers to the capacity of the hard disk. It generally refers to the size of the hard disk after the format. The larger the size of the hard disk, the better.

Second, in the choice of capacity you can also give priority to the choice of single disk capacity of large products. The larger the single disc capacity, the more advanced the technology is and the easier it is to control costs. For example, the same 40GB hard drive, if the single disc capacity is 10GB, then need 4 platters and 8 heads, if the single disc capacity up to 20GB, then need 2 platters and 4 heads, for a single disk capacity of 40GB of hard disks, as long as 1 platters and 2 head is enough, Can save a lot of costs and improve the stability of hard disk work.

2. The speed of the hard disk

This is also the question that everybody pays more attention to. It refers to the rotation speed of the spindle in the hard disk. Today, the market's IDE hard disk is mainly divided into 5400RPM (turn), 7200RPM (turn) two kinds of speed. In the case of capacity prices are the same, the preferred speed of 7200 turn of the hard disk products.

3. Transmission rate of hard disk

The transmission rate of hard disk is also one of the important parameters of hard disk. It refers mainly to the transmission rate of external and internal data for the hard disk, which is MB/s (megabits per second) or MB/sec (1MB=8MB). The external transmission rate of the hard disk (burst data transfer rate) is the burst data transmission rate of the hard disk, which generally refers to the speed of the data interface of the hard disk. Now the ata/66/100/133 interface of the hard drive transmission rate of up to 66-133mb/s.

The internal data transmission rate of the hard disk (internal data transfer rate) refers to the maximum data transfer rate between the head and the hard disk cache, in this aspect the largest internal data transmission rate of the mainstream hard disk is generally up to 350mb/s above, Excellent hard disk with its maximum internal data transfer rate up to 500mb/s.

4. Cache of hard disk

The size of the hard disk's cache is also one of the key indicators of hard disk. A hard disk cache is a high-speed memory that is inside the hard disk. Today's hard disk uses more cache types for SDRAM, but there are exceptions such as the use of EDO dram. The larger the cache, the better, it is directly related to the hard disk read speed, today's hard disk cache capacity is mostly 2M, and to 8M of greater capacity over. But there are only a few 512K cache products, this should be noted.

5. The head of the hard disk

The type of magnetic head used on the hard disk is mainly two kinds of Mr and GMR. GMR giant magnetoresistive Head has begun to replace Mr Magnetic head into the mainstream of hard disk heads.

Mr Magnetic-resistance head, which is written and read the magnetic head of the separation of the head structure, it is through the change of resistance to the signal amplitude, sensitive to the change of the signal, so that the accuracy of its reading data is also increased, and because of its read signal amplitude and track width independent, so the track can be done very narrow, This increases the density of the platters, which makes the capacity of the hard disk much more capable.

The GMR magnetic head is more sensitive to the magnetic resistance than the Mr Head, and it can achieve higher storage density than the MRI. Now the magnetic disk storage density of the Mr Head can reach 3gbit-5gbit/in2 (per square inch per gigabit), while the GMR head can reach more than 10gbit-40gbit/in2.

6. Search Time of hard disk

The hard drive seek time is also one of the important parameters to understand the hard disk. It refers mainly to the average search time of the hard disk (average seek times), the path search time (single track seeking), the maximum seek time (Max search), and the average wait time (average latency), and so on. Their units are in MS (milliseconds).

The average search time for the hard disk refers to the amount of time that the hard disk head moves to the track where the data is located, and the smaller the better, now the average search time for the IDE hard disk is below 9ms. The path-seeking time of the hard disk refers to the time that the head shifts from one track to another, and the shorter the better.

The maximum seek time of the hard disk, refers to the hard disk head from the beginning to move until the last to find the required data block the total time spent, it is the smaller the better, the market's mainstream IDE hard drive most seek time within 20ms. The average wait time for a hard disk is when the head moves to the track where the data is located, and then waits for the desired block of data to continue to rotate under the head, and its value is as small as possible.