Removing The PCB

The PCB on the underside of the drive is devoid of any surface-mounted components as this is necessary for the drive to fit within the narrow confines of a notebook hard drive bay.

Let's take a look at those surface-mounted components lurking on the other side of the PCB. To do that, we removed the screws holding the PCB to the drive.

This what the hard drive looks like without the PCB. A plastic sheet separates the PCB from the drive's underside. The cut-outs you see are for the three chips on the PCB. You can also see the contact points for the PCB.

The Controller Chips

The 250 GB Momentus 5400.4 hard drive uses what appears to be a custom-made hard drive controller from LSI. This chip manages the transfer of data between the drive and the host. It's connected to the hard drive compartment via an 18-pin connector located at the upper right corner of the drive's underside.

The LSI drive controller	The TI motor controller

Seagate also used a motor drive controller from ST Microelectronics. Again, this appears to be a custom chip, made specifically for Seagate. The main advantage of using this chip is ST's proprietary Smooth Drive pseudo-sinusoidal digital drive technology. Smooth Drive allows the hard drive to minimize torque ripple to reach a higher track density as well as reduce acoustic noise.

The Cache Buffer

The 250 GB Momentus 5400.4 comes with 8 MB of buffer memory, courtesy of a single 54-pin TSOP II SDRAM chip from Winbond.

The Winbond W9864G6GH-6 is a 64 Mbit SDRAM chip rated at 60 ns. It has a maximum bandwidth of 166 MB/s at the rated clock speed of 166 MHz.

For those who are interested in the details, this SDRAM chip supports a CAS latencies of 2 and 3, and burst lengths of 2, 4 and 8. It also has an auto-refresh feature.

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