Did you know that the main performance bottleneck in your PC is your hard drive? The hard drive is the one component that hasn’t seen any fundamental changes since it was first introduced in 1956 by IBM, and is long overdue for a replacement.

Enter the Solid State Disk (SSD). Providing sub-1ms access times, it brings performance that no standard hard drive ever could. SSDs are completely silent, require far less electricity to operate and, as they have no moving parts, are more reliable. An SSD will likely be the most meaningful PC component upgrade you will ever make.

Let’s first take a look at what makes a Hard Disk Drive slow. An HDD has 1-5 platters with a read and write head per platter. These platters are spinning discs with a thin layer of ferromagnetic material, usually 10-20nm in thickness. The write head magnetizes the material directionally to represent a “1” or a “0”. The platters typically spin at between 5400rpm and 15000rpm, 5400rpm being common for laptop hard drives and 7200rpm being common for desktop hard drives. They have a random write speed of about 1.2 MB/s, and a sequential write speed of around 80MB/s – 100MB/s. Sequential read speeds are around 80MB/s – 100 MB/s when the drive is new, and at 10000rpm random access times are around 7ms.

hard drive platter

The fastest SSDs have an access time of around 0.11ms, and random write speeds going as high as 31.7 MB/s. Sequential write speeds on some models are as high as 240MB/s and read speeds are faster as well at around 260 MB/s, close to the limit of the SATA II specification.

SSDs do lose performance over time as well, due to the fundamental way in which NAND flash works. 1 or 2 bits of data are stored per cell (1bit for SLC and 2bits for MLC), cells are grouped into pages, being the smallest readable/writeable structure in a SSD, with 4KB pages being common today. Pages are grouped together into blocks, with usually 128 pages per block. A block is the smallest structure that can be erased in a NAND-flash device,  so while you can read from and write to a page, you can only erase a block. This is where the problem lies.

TorqXFor example, if you have a block with 384KB of data and delete 128KB, as with with hard disk drives, the data doesn’t get deleted, the OS marks it as invalid. So, to the OS you have 256KB “free” space while in actual fact there’s only 128KB free in that block (256KB valid data and 128 invalid data). Now if you try to save 256KB of data to that block, the initial 256KB of valid data needs to be copied to memory(or local cache if the SSD supports it), the whole block erased, then the 512KB of data written to the block. Even while taking this delay into account, SSDs are still significantly faster than standard hard disks.

In part 2 we’ll look at the SSDs available in the South African market, how you can claim back lost performance, and why you shouldn’t purchase a SSD with a JMicron controller.

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