"computer hard drives introduced the major technical indicators" are based on book knowledge, online information, practical experience summed up the article, if you want to know more of these issues, please pay attention to the more computer Encyclopedia Forum article!
we usually buy in the hard disk, often hard to understand some of the parameters, and many magazine articles have also been a lot of explanation. However, in many cases, this description is not detailed or even a bit misleading. Today, we chat about this topic, hoping to buy the hard drive to provide proper assistance.
First of all, let's look at the internal structure of the hard disk, it will help to understand the relevant content of this article.
work, the disk in the axial motor driven, high-speed rotation, the head arm in the voice coil motor control, carried out in the disk at the top of the movement to address radial
The main technical indicators of computer hard drives introduced
1, RPM (RPM, Revolutions Per Minute): This indicator represents the hard disk spindle motor (disk drive) speed, on behalf of such 5400RPM The hard drive spindle speed of 5400 rpm.
2, Average Seek Time (Average Seek Time): If there are no special instructions generally refers to the tracking time of reading, in units of ms (milliseconds). This indicator is the meaning of receiving the hard disk read / write instruction to the heads move to the designated track (should be cylindrical, but it is the track for the specific head) above the average time needed. In addition to the average seek time, there are Road between Seek Time (Track to Track or Cylinder Switch Time) and full seek time (Full Track or Full Stroke), the former refers to the top of the head to move from the current track over the adjacent track time, which means the head from the outside (or the most inner) loop inside track at the top to move the most (or most things) the time required to circle above the track, basically more than double the average seek time. For practical work, we generally only care about the average seek time.
3, the average incubation period (Average Latency): This indicator is moving to a specific track when the head after the long wait the specified read / write head moves to the bottom sector (the disc is rotation), the disc turn faster, shorter incubation period. The average incubation period is used in a half circle of the disk rotation time. Obviously, the same speed, the average incubation period of the hard disk is fixed. 7200RPM when about 4.167ms, 5400RPM when about 5.556ms.
4, the average access time (Average Access Time): also known as the average access time, usually published in the manufacturers specifications will not be provided, which generally results in a test, its meaning is from the read / write commands sent to the first data read / write when the average time used, including the average seek time, average latency of the House and related operating time (such as instruction processing), since the House action for a very short (typically In 0.2ms or so), can be neglected, the average access time can be approximately equal to the average seek time + average latency, which is also called the average seek time. If a 5400RPM hard drive, the average seek time is 9ms, then in theory it's the average access time is 14.556ms.
5, the data transfer rate (DTR, Data Transfer Rate): units of MB / s (megabytes per second, also known as MBPS) or Mbits / s (megabits per second, also known as Mbps) . DTR is divided into the maximum (Maximum) and continuous (Sustained) two indicators, the data transfer is divided in different parties external and internal data transfer rate. DTR is the head and the internal buffer data transfer rate between the external DTR is the buffer zone and the host (ie, memory) between the data transfer rate. DTR limit depends on the external hard disk interface, the popular Ultra ATA-100 interface, which represents the maximum theoretical value of the external DTR up to 100MB / s, sustained DTR DTR is continuing to look at the internal level. DTR is the hard drive inside the real data transmission capacity, for the full play within the DTR, external DTR DTR theoretical values are higher than the internal, external, internal DTR determine the actual performance of DTR. As the disk tracks the most outer ring up, can head the unit of time more than the inner ring of the track across sectors, so head in the most outer ring within DTR when the largest, in the most inner ring within DTR when the minimum.
6, the buffer capacity (Buffer Size): Many people have called the cache (Cache) capacity, unit MB. Information in a number of manufacturers have also been writing Cache Buffer. The basic role of a buffer to balance the internal and external DTR. In order to reduce the waiting time host, will read the data before the hard disk into the buffer, so fill up before all the read or the buffer to send to the host interface to speed quickly. As technology advances, manufacturers are then added for the SCSI hard disk buffer cache functionality (which is why I still insist that it is the reason for the buffer). This is mainly reflected in three areas: prefetching (Prefetch), experiments show that in typical cases, at least 50% of the read operation is a continuous read. Prefetch function is simply the hard drive "without permission" to expand the scope to read, send to the host specified in the buffer sector data (ie, read head has been designated sector), the head and then read a number of adjacent fan data into the buffer zone, if the latter point has just read the adjacent sector prefetch, read from the buffer without re-addressing the head, increased access speed. Write Cache (Write Cache), usually in the write operation, data is first written to the buffer and then sent to the head, so head to write the report after completion of host write is completed, the host began to deal with the next task. Hard disk with write cache data is written to ease in the area after the report is written to the host has finished, let the host ahead of time to "liberate" other matters (the rest of the host need not wait for the write heads), to improve the overall efficiency. To further improve performance, manufacturers now have applied the basic sub-caching technology (Multiple Segment Cache), the buffer is divided into multiple small pieces and write data stored in different, but do not waste the buffer zone for small data space, It also can be so unified after all paragraphs written, write, better performance. Read cache (Read Cache), will read the data off temporarily stored in the buffer, if necessary, the host can once again directly from the buffer provided speed. Reading also can make use of sub-cache technology, store multiple disparate data blocks, the cache read data more than to further improve the cache hit rate.
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Hard common technical indicators are the following:
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