Read/write head

Magnetooptic Materials. The appHcation of magnetooptic effects to optical memory systems, such as for laser beam writing and magnetooptic read, has been the subject of much research. Magnetooptic storage media offer the potential of storing over 120 Mbit/cm of information without contact of the read/write head which would thus be very competitive to floppy disks and tape. 

Figure 7 SFM image of a thin-fiim read-write head showing magnetic poles (dark rectangles) recessed 200 A.

Fig. 5 Schematic of the read/write head-magnetic disk interface.

Luo et al. [1,153] used a slurry containing ultra-fine diamond (UFD) powders to polish the surface of HDD sliders. The powders are from 3 nm to 18 nm in diameter and 90 % around 5 nm. They are crystal and sphere-like [154]. The pH value of the slurry is kept in the range from 6.0 to 7.5 in order to avoid the corrosion of read-write heads, especially pole areas. A surface-active agent is added into the slurry to decrease the surface tension of the slurry to 22.5 Dyn/cm, and make it spread on the polish plate equably. An anti-electrostatic solvent is also added to the slurry to avoid the magnetoresistance (MR) head being destroyed by electrostatic discharge. The anion concentration of the slurry is strictly controlled in ppb level so as to avoid the erosion of magnetic heads as shown in Table 5. The concentration of UFDs in the slurry is 0.4 wt %. 

Actually, read/write heads in combination represent somewhat older technology it should thus be remembered that in newer technologies, there is a clear trend toward using separate heads for reading and writing (2). 

The second contribution spans an even larger range of length and times scales. Two benchmark examples illustrate the design approach polymer electrolyte fuel cells and hard disk drive (HDD) systems. In the current HDDs, the read/write head flies about 6.5 nm above the surface via the air bearing design. Multi-scale modeling tools include quantum mechanical (i.e., density functional theory (DFT)), atomistic (i.e., Monte Carlo (MC) and molecular dynamics (MD)), mesoscopic (i.e., dissipative particle dynamics (DPD) and lattice Boltzmann method (LBM)), and macroscopic (i.e., LBM, computational fluid mechanics, and system optimization) levels. 

The enhanced storage is due to the 1571 s double-sided design (there are two read/write heads), so you ll have to use... 

Another quality that is used to gauge the performance of an individual drive is seek time. This value, commonly given in milliseconds (ms), is how long it takes the actuator arm to move from rest to the position where the read/write head will access information. Additionally, because the platters rotate, once the read/write is in position, it may take a few milliseconds for the target sector to move under the read/write head. This delay is known as the latency factor. Latency values are given in milliseconds (ms). 

There are many ways of converting Is and Os to flux transitions. The simplest way is to interpret the presence of a flux transition as a 1 and the absence as a 0. Because this was the most obvious choice, the first hard disks (ST-506, ESDI types) used this method of encoding, known as Frequency Modulation (FM), and its cousin Modified FM (MFM). This worked well until techniques for increasing the track/cylinder density became almost too successful. What happened was that tracks would be placed so tightly together that at higher speeds, the read/write heads would affect not only the track immediately under the head, but the adjacent ones as well. 

A floppy drive has either one or two read/write heads. Each head moves in a straight line on a track over the disk rather than on an angular path as with fixed disk systems. When the disk is placed into the drive, a motor engages the center of the disk and rotates it. This action moves the tracks past the read/write heads. 

The final type of removable media drive is a tape drive (see Figure 4.6). The tape cartridge uses a long polyester ribbon coated with magnetic oxide wrapped around two spools. As the tape unwinds from one spool, it passes by a read/write head in the drive that retrieves or saves the information. It then proceeds to the other spool where it is kept until needed again. 

The 514-inch floppy disks are made from a polyester disk coated with iron oxide and a flexible outer covering. The disk has a large hole in the center, called the drive hole, that is used by the motor in the disk drive to spin the disk. In addition, there is also a 114-inch oval window cut into the case to allow the read/write heads access to the disk media. A small round hole cut into the disk shell next to the drive hole lines up with an even smaller hole cut into the disk media. When this smaller hole spins past the slightly larger hole in the shell, it allows a light to shine all the way through the disk system. In this way, the floppy drive can tell how fast the disk is rotating by how many times in a second that hole appears. 

One of the most common problems that develop with floppy drives is misaligned read/write heads. The symptoms are fairly easy to recognize—you can read and write to a floppy on one machine but not on any others. This is usually caused by the mechanical arm in the floppy drive becoming misaligned so that the format it creates is not properly positioned on the disk (thus preventing other floppy drives from reading it). 

---