What are the Differences between SSD (Solid State Sisk) and HDD (Mechanical Hard Disk)?| Part 1

We already knew about ‘What’s the Hard Disk Drive (HDD) and What’s the Solid State Drive (SSD)‘ in last article.

Then what are the differences between a solid-state drive and an ordinary hard drive? How do you choose when faced with both?

The big difference between SSD (solid state disk) and HDD (mechanical hard disk) derives from their structures, SSD is of all-electronic structure applying integrated circuit storage technology, and it uses memory chips and addressing controller to form a hard drive, which is similar to U disk technology, without any mechanical moving parts.

The traditional mechanical hard disk HDD uses high-speed spinning disks to store data, and reads and writes through a magnetic head, which has a delay in the mechanical movement and cannot read/write at multiple positions simultaneously.

1. Performance

Solid-state drives are completely different from mechanical hard drives in structure. Solid state hard disk starts fast without motor speeding up process.

The greatest advantage of solid-state hard drives is its little seek time. Solid-state drives are acting as a common disk in the operating system, and users can definitely use it as a storage medium. Because of the full use of Flash storage media, there is no mechanical structure inside, so there is no data search pause, delay time or seek time. As is known to all, the mechanical properties of common hard disk seriously limit its speed of data read and write, the biggest bottleneck for computer operation speed is right on the hard drive, so the emergence of solid-state drives could exactly breakdown this bottleneck.

Through the above transfer rate test chart, we can see that solid-state drives perform excellent, along the wavy curve, the minimum transfer rate is 91.2 MB/S, and the average transfer rate is 135.7 MB/S, although which has a certain gap with the nominal 170MB/S maximum rate, compared with the mechanical hard disk with a speed of only 63 MB/S, SSD has achieved considerable results. It is worth mentioning that we have presented in the introduction of solid-state drives that solid-state drives use random access without magnetic head structure, so its seek time is very close to zero, which is a result that mechanical hard disk can never achieve.

During the test, instantaneous transfer rate of mechanical hard disk plunges to 9.8MB/s, while the solid state disk has a wavy curve, with the minimum and maximum transfer rate relatively stable.

2. Different fundamental principles of read and write

SSD applies master read and write nandflash, while mechanical hard disk reads through magnetic head on rotating disc; and the read/write mode is also different, SSD is bitwise access (this is why some models have writing speed of 240 GB, which is lower than 480 GB), while mechanical drive can be deemed as sequential access, which is why SSD does not need to do defragmenter, and mechanical drive mechanical hard drive must be defragmented once it has been used for a long time;

3. Different read and write speed.

Here is the system startup and software startup time comparison and data read latency comparison:

Solid-state drives do random read quickly without magnetic head, and the read latency is minimal. DRAM base SSD writes very fast.

For continuous reads and writes, now the sata3 SSD has basically reached the theoretical value of sata3, which is about 500, while continuous reads and writes of 7200 RPM single disc 1T disk is up to about 170.

That is, small file reads and writes, at this point, SSD performs far better than mechanical hard drives.

For average reads and writes, the maximum reads and writes of the disk only appears in the outer circle of the disc, as the outermost of circle has the fastest line speed, the speed turns slowly as the head moves in, however, the speed of SSD basically is a horizontal line.

For access time, SSD’s access time is much shorter than that of HDD since it does not require physical seek time.

According to related tests, with two computers under the same configuration, it took only 18 seconds from boot up to the desktop displaying for a laptop carrying a solid-state drive; and for the one carrying a traditional hard disk, it took a total of 31 seconds. Almost a double gap happens between the two. Solid-state drives possess a huge advantage in transfer speed, which is up to 500M/ SEC; the reading speed reaches 400-600M per second, and the writing speed can be as high as 200M per second. It takes only a few seconds to handle a 1G file. Unfortunately, the read speed of traditional IDE hard disk cannot break the limit of 200 M per second, and the write speed has difficulty to exceed 100 M per second, it is basically dozens MB per second. So it is a good choice for users who often need to read or handle large files to use SSD. The read time is relatively fixed. The disk fragment does not affect the read time as the addressing time is independent of the data storage location.

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