Here, even to just write 4KB, the controller must read an entire block (512KB), update the single page, and write theentire block back out. When that time comes, you run into a nasty situation called the read-modify-write. You write in pages (4KB) but you can only erase in blocks (128 pages or 512KB) thus SSDs don't erase data when you delete it, only when they run out of space to write internally. The falling performance was actually a side effect of the way NAND Flash works. The problem is that the SSD's performance can decline as it fills up. You should also buy an SSD that supports the TRIM command built into Windows 7 to avoid what Anand Lal Shimpi of Anandtech calls "stuttering crap". When you do a clean installation from the Windows 7 system disc, it will partition and set up the SSD correctly aligned, install the correct drivers, and disable things like Prefetch and Superfetch that are no longer required. Basically, Windows 7 and Vista don't load drivers for storage systems that are not being used, so if you change from SATA to AHCI it won't load the Msahci.sys driver needed to read the SSD. With an SSD,you may need to change this to AHCI (Advanced HostController Interface). PCs are typically set up to use SATA (Serial Advanced Technology Attachment) to attach hard drives. So, to get the full benefit of an SSD, it's better to do a clean installation of Windows 7.īefore installing Windows 7, you may need to go into your PC's BIOS and change the hard drive setting. (See Ed Bott's Windows 7 and SSDs: Setup secrets and tune-up tweaks.) You can, of course, "clone" a laptop hard drive to an SSD, but that will produce an SSD that's set up to work as a hard drive. These routines are not needed with SSDs, and the defragging can be considered harmful. For example,Windows 7 optimises the hard drive using Prefetch and Superfetch, and does some automatic defragmentation. However, hard drives and SSDs are not the same, and Windows 7 – the only version of Windows designed to work with SSDs – treats them differently. Swapping one hard drive for another is generally pretty simple, because you can "clone" one to the other. In other words,if you intend to do this, you need to know what you are doing, and you should be prepared to take responsibility. Also, if something goes wrong with your PC, the manufacturer is unlikely to support it, and would probably ask you to replace the original hard drive. You can do this fairly easily, and you will get some benefits, but the SSD is unlikely to work at its best. However, many manufacturers supply SSDs in hard drive-style cases so that the SSD can be slotted into an ordinary laptop, replacing the original hard drive. These PCs may well use SSDs that resemble sticks of memory chips, like the Toshiba Blade X-gale first used in Apple MacBook Airs. If you want to use an SSD as the system disk in a PC running Windows 7, it would be best to buy a new PC that has been designed for the purpose. Of course, if you are using a laptop on mains power, you can set the hard drive to keep running all the time, and minimise this particular problem. This can make a laptop with an SSD feel much more responsive. SSDs don't spin, and don't need to be restarted, so they can be read instantly. When a program wants to read that hard drive, you have to wait until it gets back up to speed. SSDs are particularly beneficial in laptops where the hard drive is allowed to stop spinning when it's not in use.
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