RAM and storage speed

It is interesting to look at the speed of file storage as RAM speeds have increased. I am using the fastest file load/save method (RAMfs) plus the fastest file load/save method to a non-volatile store (SATA where present else the SDFS or Solid state HD or whatever.

I am therefore quoting the theoretical RAM to RAM transfer speed determined by the speed of the RAM bus, the transfer speed using RAMfs [to illustrate the overheads of the filing system itself], and the current speed for the relevant hard disc. The overheads of the filing system method itself [i.e. RAMfs transfer speed] govern the speed achievable with hard disc storage.

The Risc PC (StrongArm) had a processor much faster than the one the machine was designed for and so the RAM was the bottleneck – hence the transfer speed approaches the theoretical maximum RAM transfer speed. Most recent machines seem to have the filing system overhead and the processor throughput as the governing item?

Hence whatever development takes place on drivers for fast storage there is currently not much headroom above about 100Mbyte/s except on Virtual Risc PC.

Do you have comparative figures for the Pi (either model)?

For the Pi see here – I don’t know its memory bus speed but read/write speed to RAMfs is 96 (Pi 1) – 218 (Pi 2) and HD peak speed is 9.6 (Pi 2) to 20.3 (pi 1).

I also note that the maximum eSATA speed is 375Mbyte/s anyway (3Gb/s).