Installing a 2.5" HDD

As it is mentioned above, 3.5" hard drives dissipate significantly more heat than the 2.5" laptop-size ones. In fact, this makes it necessary to use the case fan. As an improvement one can consider using a 2.5" HDD. Below is a picture of two 80Gb Seagate HDDs. The one on the left is a Seagate Momentus 5400.3 ST980815A 80GB 5400 RPM ATA-6. This disk has a single platter design and therefore has only two heads on each side of the disk, which is a minimum. In general, the numbers of heads is twice the number of platters. Less heads automatically means less mass to move during the seek resulting in lower noise. I use an external USB HDD for the personal data, backup, and rarely used large files. This external HDD is off most of the time also for the security reasons and completely solves the storage problem. There is no need in the system fan in this setup anymore. The 2.5" HDD is practically cold and silent as well as the entire PC where just the HDD has moving parts. My 2.5" HDD features only 5400 RPM vs. 7200 for the 3.5" one, but for my applications I have not noticed any difference. There are 7200 RMP 2.5" HDDs available though, but they are slightly noisier and dissipate a bit more heat.

However, there was a serious problem with the cable. The 2.5" PATA HDDs use a 44-pin connector vs. 40-pin one used in desktop computers. The extra 4 pins on the connector are used for the power. Furthermore, the motherboard also has a 40-pin IDE connector installed. The 44-to-40 pin cable supplied with the motherboard (the second one on the left) has only 40 conductors. With this cable the BIOS sets the HDD in the UltraDMA-33 mode only while the drive interface supports UltraDMA-100. To achieve a higher data transfer speed a 80-conductor cable is needed. Only 40 conductors in this cable are used to transfer data, the other 40 just separate the data conductors preventing an interference. I could only find 40-to-40 UltraATA cables (the first and the third ones), which do not fit to the drive connector. A solution is to use a 2.5" to 3.5" HDD adapter and a standard 10" UltraATA cable. I used Rosewill RCW-603 adapter shown on the right. The +5V pin of this adapter is internally connected to pins 41 and 42 to power up the drive logic and motor, respectively. Make sure to apply a jumper to set the drive into the "Cable Select" mode.

To eliminate the HDD noise completely, one can put it on a power-saving mode, which shuts it down after a certain period of inactivity. This way improved mini-PC is too silent now. I do not hear it at all, the only indication that it is on is the front blue LED. Late evenings, when it gets very silent around, I still do not hear the PC, but started to recognize a low-frequency 60Hz buzz coming from the LCD monitor, which has a built-in power supply. This was not the case before, as this tiny noise (not noticeable at all during the day) was efficiently masked out by other PC noises. I wish I had less sensitive ears :)