Study on the technical Index system of computer product evaluation and its storage

(i) Internal storage (memory) performance indicators

(1) speed ( access Time )--memory speed is generally used to access data once the time required (in general NS) as a performance indicator, the less time, the faster.
(2) Capacity--memory is the main part of the computer, it is relative to the external memory. The more memory is the better, but to be limited by the maximum capacity of the motherboard support, and is the current computer, this limit is still blocked.
(3) Number of memory lines-refers to the number of points of contact between the memory and the motherboard, these contact points are gold fingers, there are 72 lines, 168 lines and 184 lines. 72-, 168-, and 184-wire memory bar data widths are 8-bit, 32-bit, and 64-bit respectively.

(ii) Performance indicators for external storage

1. Mechanical Hardware Performance Index

(1) rpm (rpm,revolutions per Minute): This indicator represents the speed of the hard drive spindle motor (drive disk), such as 5400RPM means that the spindle speed of the drive is 5400 rpm per minute.

(2) average seek time (Average seek times): If no special instructions generally refer to the seek time when reading, the unit is MS (MS). The meaning of this indicator is the average time required for the drive to move to a specified track (which should be a cylinder, but a track for a specific head) after it has received a read/write instruction. In addition to the average seek time, there is also an inter-lane seek time (track-to-track or cylinder Switch time) and the full-track-seek-times (fully-tracks or complete Stroke), which refers to the time required for the head to move above the adjacent track from the current The latter refers to the time required for the head to move above the outer (or most inner) lap track to the top (or most outer) lap track, which is substantially more than the average seek time. We generally only care about the average seek time for actual work.

(3) average incubation period (Average Latency): This indicator refers to how long the specified read/write sector is moved to the bottom of the head (the disc is rotated) when the head is moved to the specified track, and the faster the disc, the shorter the incubation time. The average incubation period refers to the time it takes for the disk to turn half a circle. Obviously, the average incubation period for the same speed drive is fixed. Approx. 5.556ms at 7200RPM at approx. 4.167ms,5400rpm.

(4) average access time (Average access times): Also known as average access time, is generally not provided in the manufacturer's published specifications, which is generally a test score, which means the average time from the read/write instruction to the first data read/write, Including the average seek time, the average incubation period and related housekeeping time (such as instruction processing), because the house operation time is generally very short (generally around 0.2ms), negligible, so the average access time can be approximately equal to the average seek time + average incubation period, and thus also known as the average addressing time. If the average seek time for a 5400RPM hard drive is 9ms, the average access time in theory is 14.556ms.

(5) data transfer rates (DTR, data Transfer rate): MB/s (megabytes per second, also known as Mbps) or mbits/s (megabits per second, also known as Mbps). DTR is divided into maximum (Maximum) and continuous (sustained) two indicators, depending on the data of the handover side and the external and internal data transfer rate. Internal DTR refers to the data transfer rate between the head and the buffer, and external DTR refers to the data transfer rate between the buffer and the host (that is, memory). The external DTR upper limit depends on the interface of the hard drive, the current Ultra ATA-100 interface represents the external DTR maximum theoretical value of up to 100mb/s, continuous DTR depends on the level of internal continuous DTR. Internal DTR is the real data transmission capability of the hard disk, in order to give full play to internal DTR, the external DTR theory value is higher than the internal DTR, but the internal DTR determines the actual performance of external DTR. Due to the longest outer ring track in the disk, it allows the head to cross more sectors than the inner ring's track in the unit time, so the head is the largest within the outer ring, and the internal DTR is the smallest in the inner ring.

    (6) buffer capacity (buffer Size): Many people also call the cache capacity in megabytes. The cache Buffer is also written in some vendor profiles. The basic function of the buffer is to balance the internal and external DTR. To reduce the host's wait time, the hard disk will read the data into the buffer, and so on all read or buffer filled, and then quickly sent to the host at the interface rate. With the development of technology, the manufacturers later added caching capabilities to SCSI hard disk buffers. This is mainly reflected in three aspects: Prefetch (Prefetch), experiments show that in typical cases, at least 50% of the read operation is continuous reading. The prefetch function simply means that the hard disk "privately" expands the read range, after the buffer sends the specified sector data to the host (that is, the head has already read the specified sector), the head then reads the contiguous slices of the sector data and feeds into the buffer, if the subsequent reads exactly point to the adjacent sectors that have been prefetch, The access speed is improved by reading from the buffer without the head re-addressing. Write cache, usually in the case of write operations, the data is written to the buffer before sending to the head, when the head is written and then report the host write, the host will start processing the next task. A hard disk with write cache will report write completion to the host after the data is written to the buffer, allowing the host to "free" processing of other transactions in advance (the remaining head write operations master does not wait), improving overall efficiency.

In order to further improve the performance, the current manufacturers have basically applied the segmented cache technology (multiple Segment cache), the buffer is divided into a number of small pieces, storage of different write data, rather than waste the entire buffer space for small data, You can also wait for all segments to write and write uniformly, with better performance. Read cache, which temporarily stores the read data in a buffer, which can be provided directly from the buffer if the host is needed again, to speed up. Read caching can also use segmented technology to store multiple disparate chunks of data, cache multiple read data, and further improve cache hit ratios.
(7) noise and temperature (Noise & temperature): These two belong to non-performance indicators. For the noise, before the manufacturers do not care, but from 2000 onwards, for the needs of the market (such as OEMs want to produce a quieter computer to increase the selling point) manufacturers through a variety of means to reduce the work of the hard disk noise, the third version of the ATA-5 specification also added a subset of automatic acoustics (noise) management (AAM, Automatic acoustic Management), so all new hard disks currently support AAM functionality. The noise of the hard drive mainly comes from the spindle motor and the voice coil motor, noise reduction is also from the two points (the increase in the disk will also increase the noise, but there is no way). As for heat, in fact each manufacturer has its own standards, and claimed that the performance of the hard drive is what they expected, completely within the scope of security, no problem. This is not to worry about, but the key is that the hard disk is a part of the chassis, its high heat will increase the overall temperature of the chassis, perhaps the hard disk itself is nothing, but may not be able to withstand the accessories around, other do not say, if it is two high-heat hard disk installed very close, then it can withstand nearly double heat? So the heat of the hard drive still needs to be noticed by manufacturers.

2. Solid-State Drive performance metrics

(1) is read/write speed MB/s

(2) The second is the random reading and writing ability, the unit is IOPS, that is, the number of read/write (I/O interface) operations per second.

Study on the technical Index system of computer product evaluation and its storage