Those who are looking for a fast drive usually look for an SSD these days. But in addition to SSDs and HDDs, there are also hybrid drives, so-called SSHDs (Solid State Hybrid Drives), which represent a combination of a hard disk and a cache of several gigabytes of flash memory. The additional memory is intended to accelerate read access in frequently used applications. The Seagate Momentus XT from 2010 is undoubtedly the best known in this market segment, but Toshiba and Seagate also have more current models in their range, which offer up to one terabyte of storage space.
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Whether at Toshiba or Seagate, the flash memory of the SSHDs is only used for buffering read access, Shortly after the release of the Momentus XT, Seagate announced that a firmware upgrade would also allow write access to be buffered, but this announcement has remained to this day.
In terms of their functionality, the drives from both manufacturers are similar: A 500 to 1,000 gigabyte 2.5-inch hard drive is supplemented by an eight gigabyte internal NAND flash cache. The Toshiba drives and Seagate's Momentus XT are SLC-NAND, MLC memory is used in the newer SSHDs from Seagate.
The algorithms of the firmware automatically fill the flash buffer with data that the user accesses frequently, constantly adapting to the current usage behavior. A significant improvement can be seen after just two to three starts. The data on the hard disk is retained, there is only a copy in the flash buffer, which can be accessed very quickly. Write access, on the other hand, always ends up directly on the hard disk, here there is no performance advantage over normal hard disks.
The average user benefits from higher performance, especially in those areas that are noticed first in everyday life, namely when the computer is started up and when applications are started that are loaded faster from the flash buffer thanks to much shorter access times and parallel data access.
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