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All 60 GB SSDs I have found available have a write speed of around 90 MB/s, whilst 120 GB SSDs and higher have upwards of 400 MB/s.

Both have similar read speeds of around 500 MB/s and upwards.

Is there some technological issue that prevents higher write speeds in smaller volume SSDs whilst not affecting read speeds? If so, what is it?

It is suggested below that a RAID 0 configuration could be being employed in the larger drives; this would increase the write speed of the higher end disks while leaving the read speed to be determined by the SATA III connectors. Can anyone cite sources in support of this?

Here are some vendor-provided speeds from Transcend's SSD product fact sheet, available (PDF) in French and in English:

              Reading speed/Writing speed
Size        Sequential         Random access
32GB     230MB/s, 40MB/s       90MB/s, 40MB/s
64GB     450MB/s, 80MB/s      170MB/s, 80MB/s
128GB    550MB/s, 170MB/s     270MB/s, 170MB/s
256GB    560MB/s, 320MB/s     300MB/s, 300MB/s
512GB    560MB/s, 460MB/s     300MB/s, 300MB/s
1TB      560MB/s, 460MB/s     300MB/s, 300MB/s

I bought 60 GB, 120 GB and 240 GB drives from the same manufacturer and disassembled them.

This is the 60 GB drive: 60GB Devro

This is the 120 GB drive (had to be removed from case to see the chips): 120GB Devro

This is the 240: 240GB Devro

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    The small SSD's are probably older, or lower grade stock. – user1751825 Sep 30 '16 at 1:11
  • 60GB SSDs use slower older hardware. Besides that fact there isn't any reason the newer faster hardware couldn't be sold in smaller sizes. Consumers just demand larger sizes so that isn't done. The speed delta isn't that large. – Ramhound Sep 30 '16 at 1:11
  • Do you happen to have specific examples? e.g. Are they within one series by a single manufacturer? Generally, higher capacities are faster because they have more NAND chips that can be accessed in parallel, might have more cache space (SLC cache on MLC/TLC NAND), DRAM, etc.. – Bob Sep 30 '16 at 1:56
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    @Matthew I believe it is not strictly RAID0 but the memory chip controller just has more outputs which should spread the write more evenly among memory chips. The read speed is limited by the interface used to connect said chips to the controller. – Martijn Oct 1 '16 at 21:27
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    @Matthew read is much faster than write thus being limited by the interface, not the chips or controller. – Martijn Oct 3 '16 at 14:51
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I believe it's because larger SSDs use more memory chips, and so can process more data simultaneously. This post explains it with some more depth.

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  • Ok, I will be able to verify this shortly. After opening the 120GB drive I can see it has just 2 memory chips. I suppose if your suggestion is correct then we could expect 1 chip in the 60GB drive. 60GB and 240GB drives arrive tomorrow, I will upload the pictures as soon as they get here. – Matthew Oct 3 '16 at 14:55
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This website offers the history of SSDs up to the current age. If you truly are curious about how SSDs have advanced through the last couple of years.

However the TDLR answer to your question is simple: The older smaller drives have slower read/write speeds because of the technology used to create them. When they were created the tech wasn't as powerful as it is today so they were only able to make drives of that size at a certain speed. As our technology has increased so has the standard drive sizes and the speed of said drives.

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  • The information from the website does not give much/any insight into the question - it took a long time to read and work that out. Also, the 60GB drives are being produced today - these are not last years drives but rather recently produced drives. In fact, I have found references to a Sandisk Ultra 60GB that was released 3 years ago that had a write speed of 270Mb/s, but this is no longer in production > newegg.com/Product/Product.aspx?Item=N82E16820171544 – Matthew Oct 1 '16 at 21:18
  • @Matthew, without getting into the veracity of the argument, just the aspect of older technology, a lot of money goes into development, tooling, etc. Also, as better chips come along, the older, less-capable chips become cheap. As long as there is a market, it makes economic sense for the manufacturer to continue to produce drives using the older technology. – fixer1234 Oct 7 '16 at 20:09
  • @fixer1234 Ok, so it could simply be that older, more available chips are being sold off in new boxes. I am starting to see why this question can be seen to be too broad, thank you for taking the time to respond. I would point out, for the sake of clarity, that the original question was about why there was a difference in write speed but not in read speed, which seems less related to changing technology and more related to continuing trends in the abilities of current technologies. Maybe I did not make this clear enough... – Matthew Oct 7 '16 at 20:39
  • I have updated the question title to make this clearer. – Matthew Oct 7 '16 at 20:41
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Although I'm not too sure on the exact answer, I've just always thought that it would make sense as there's really no realistic point of a 60GB SSD drive having 2GB/s transfer speeds when it would only take ~30 seconds to process the entire disk. There would be far less space to transfer files, ultimately meaning the speeds wouldn't have to be as high as those of higher capacities (256GB, 512GB, 1TB+).

Yes, age may also be a factor for some drives but that's not always the case as a lot of modern low capacity drives have fairly low speeds compared to their higher models which is why I believe that these speeds are there by design in an attempt to reduce manufacturing costs, time etc.

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