Logic Board

On the logic board you will find all circuitry in charge of controlling the hard drive. In these days of highly integrated devices, you will find just three or four big integrated circuits on the logic board, as you can see on Figures 4 and 5. Take a look at the pictures as we will explain more about the circuits pictured below.

Hard Disk Drive Logic BoardFigure 4: Logic board from an ATA hard drive.

Hard Disk Drive Logic BoardFigure 5: Logic board from a SATA hard drive.

The big circuit is the controller. It is in charge of everything: exchanging data between the hard drive and the computer, controlling the motors on the hard drive, commanding the heads to read or write data, etc.

Optionally there is a Flash-ROM circuit where the hard drive firmware is located. Firmware is the name given to a program that is stored inside a ROM (Read Only Memory). The hard drive firmware is the program its controller executes. Sometimes this device is embedded in the controller, as it happens on the hard drive in Figure 5.

The controller doesn’t drive enough current to turn on or move the hard drive motors. So all hard drives use a motor driver chip. This chip is a current amplifier. It takes the commands sent from the controller to the motors and passes them to the motors, but with a higher current. So, this chip is located between the controller and the motors.

The fourth main chip you can find on a logic board is the RAM (Random Access Memory) chip, also known as buffer. This chips has an ultimate role in the hard drive performance. The higher its capacity, the fastest the data transfer between the drive and the computer will be. You can find out the capacity of your hard drive buffer on the chip manufacturer’s website. For example, the memory chip in Figure 4 is a Hynix HY57V161610DTC chip. Going to Hynix’s website at you can find this is a 16 Mb (Megabit) chip. The capacity of memory chips is given in Megabits, while we use Megabyte to refer to memory capacity. Thus we need to divide the value given in Megabit by eight in order to have the value in Megabyte. So, this chip is a 2 MB (Megabyte) chip, so this hard drive buffer is of 2 MB.

In Figure 5, you can see another chip, which is a SATA/ATA converter chip. A lot of manufacturers instead of designing Serial ATA controller chips simply pick ATA controller chips and add a converter chip to convert the hard drive Serial ATA interface into regular ATA. This is the case of the hard drive in Figure 5, which uses the Marvell 88i8030 converter chip. So even though this hard drive has a Serial ATA interface, it is not a “true” Serial ATA hard drive (it is not a “native” Serial ATA hard drive), since its controller chip is still ATA.

You may be wonder how do we know the function of each chip on the logic board. Actually it is fairly simple and you can learn the trick from us. Just type in the numbers located on the first line of the chip package on Google and it will return a lot of information about the chip! For example, for the Flash-ROM used on the hard drive in Figure 4, just type in M29F102BB and the first item returned will be a page on ST Microelectronics with all technical details of this chip.


Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.