Question Why don't they use multiple cheap DDR-333 as last resort ram through SATA III


Jul 1, 2019
Since it has a similar frequency and if they can daisy chain it can end up being cheaper than a whole new system or using paging files and breaking endurance of an SSD with the little DRAM
Because ram is volatile, ie literally 'loses its memory' when power is lost. Plus, the memory controller for system memory is much different than for drives. So it's like using an orange in a banana milkshake--it just won't work.
There was a product like this, the Gigabyte i-RAM. It used sticks of DDR-200 to DDR-400 and put them onto SATA-I as just a regular drive. You could use it as a ReadyBoost-like drive cache with the use of software, It came with a battery backup.

It was most fun back in the days when you could install Win9x to it as it had 1/10th the latency of even the fastest SSDs. Later on I used it to put a pagefile on for 32-bit systems which could only access 4GB of actual RAM, however when system RAM became cheap enough I instead used RAMdrive software to put the pagedrive on otherwise inaccesible RAM above 4GB. I never was able to use it for ReadyBoost itself but heard of some workarounds to allow that

BTW just about every HDD in the world does already have a RAM cache, usually something small like 16MB. The i-RAM allowed 4GB, and RAMdrives are only limited by how much system RAM you'd like to dedicate for a drive cache. Obviously it makes no sense to put a pagefile onto a RAMdrive of a 64-bit system, but some poorly written programs do benefit from a scratch disk there.

This is a good question because all of the usual technologies you can think of for this used memory with a limited write cycle life, such as Intel Turbo Memory (SLC), Condusiv ExpressCache/Sandisk ReadyCache (which used MLC!) and Intel Optane (3D XPoint). There have also been various hybrid drive arrangements to combine a HDD with some flash such as Apple Fusion Drive or Intel SRT which could presumably be used with an i-RAM-like device, and of course Seagate had their SSHDs which integrated a large SLC cache into a HDD.
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You know, I forgot about the i-ram and such devices. And with today's memory sizes and tons of obsolete ddr3 ecc reg readily available, I wonder what a modern iram might look like? It wouldn't be a device for everyone, but for for certain applications that require even faster access or higher iops (like some zfs operations), these type of devices would really make sense as someone could take some spare ddr3 ram, load it up, and have an ultra fast hardware cache.

Ramdrive and smartdrv back in the day really could utilize the heck out of spare memory. I still remember when we had 32mb in our 486 and smartdrive used 16mb of that--everything flew once it was cached.