August 9th, 2011, 03:32 AM
Using a CF card as hard disk?
Hello, I wanted to buy a CF card to use as a hard disk. I do not need a lot of space (8GB or 16GB should do fine) and I wanted to profit from the "supposedly" increase in speed being a direct access memory.
However my problem is that I no longer think that a CF card will be faster then let say a conventional hard disk... I do not know if I am wrong, but here is my reasoning ...
SanDisk CF card that transfers at 30MB/s. There are other CF cards that transfer at 90MB/s. However I went to read on Wikipedia and found the following ... "As of 2010, a typical 7200 rpm desktop hard drive has a sustained "disk-to-buffer" data transfer rate up to 1030 Mbits/sec"
1030 / 8 = 128MB/s
Used following for conversion ...
This is a jump even over a 90MB/s CF card (which is quite expensive) ...
So the question is ... does it really make sense to use a CF card? considering I was hoping to get a speed boost when using this?
August 10th, 2011, 11:09 AM
I am asking this question because I want my machine to boot up as quickly as possible and at this point I am no longer sure if such a thing is possible with a CF card. Also from wikipedia I found the following ...
"A direct motherboard connection is often limited to 33 Mbyte/s because IDE to CF adapters lack high speed ATA (66 Mbyte/s plus) cable support. Power on from sleep/off takes longer than power up from standby."
Therefore I was wondering, does a normal disk really transfer 128MB/s? or this is the maximum possible but in reality this number is far less?
August 10th, 2011, 09:26 PM
"disk-to-buffer" is an ideal speed; the drive has to find the data first, and after the data is read to the buffer is still has to be transmitted over the bus (IDE or SATA) back to the motherboard.
Use a solid state drive instead. I doubt you will get good performance from a CF card.
IDE connections have a maximum theoretical capacity of 133MB/s. A 7200 RPM mechanical drive will rarely saturate this bus. You will normally see average read rates of 60-90 MB/s from a 7200 RPM mechanical drive.
A solid state drive will easily saturate an IDE connection; thus you won't find any that use it. A SATA 3Gb/s or 6Gb/s connection is required to provided the needed bandwidth for these drives. Read speeds for SSDs vary drastically, but even a budget drive can easily sustain average read speeds of 150-200 MB/s plus.
You can also buy SSDs with advertised read speeds of over 400 MB/s with advertised write speeds of over 200 MB/s.
In addition to the actual sustained read speed, SSDs have a drastically lower seek time than mechanical drives. The seek time of an SSD is generally about 0.1ms compared to about 5ms for a 7200 RPM mechanical drive. This matters a lot more for boot time than the raw read speed, since booting usually involves reading many small files rather than a few very large ones.
You can also boost performance by setting up a RAID array of mechanical drives.