Hard Disk Drives, Optical Units, and File Systems
The processing of information is important, but it requires a storage system. It is necessary to have systems that can save information, at least for a limited time. The evolution of these systems has been guided by two key parameters: storage capacity and speed.
Hard Disk Drives
A hard disk memory storage system is valid, as it was some time ago, but its volatility makes it unsuitable for long-term data retention. This is where the need for hard drives arises. A hard drive is hermetic, and its elements are only, in rare cases, worth repairing. Hard drives have evolved to optimize their main parameters: access time and capacity. They are the answer to the need for storage.
Speed is the first of the demands. Access times are getting shorter, between 8 and 10 milliseconds. A key parameter for time reduction is the increased speed of rotation.
Reliability is measured in MTBF (Mean Time Between Failures), which measures the time between failures, expressed in thousands of hours. In the field of reliability arises *S.M.A.R.T.* (Self-Monitoring, Analysis, and Reporting Technology) software, which provides reporting and monitoring of real-time disk status.
Performance: Hard drives contain platters that are covered by a magnetizable substrate. These platters are locked inside the case. The read/write heads fly over the platters at a minimal distance, sometimes even seeming to graze them. This is not a problem due to a super-slippery substance that makes this contact harmless.
Longer components reduce points of failure. The disc has, at the bottom, a pre-controlled electronic circuit for parallel writing and series-parallel reading. It controls the position of the heads and ensures constant speed.
Latency: The time it takes for the disc to pass under the reading head. Speeds are typically 7500 to 10,000 RPM.
Data bus: 40 or 80 threads. 40-pin connector.
Wiring: Pin 1 is red.
Cylinders, heads, and sectors.
Optical Units (CD/DVD)
Optical units have quickly become an indispensable element. One advantage of an optical system is the ability to store and read data. A DVD is essentially a CD optimized with specific improvements. *Pits* are holes in the tracks of the CD.
Operation: In essence, the interpretation of 0s and 1s is done by reflecting a laser beam. A pale area can be mirrored or not, creating variations. This binary system is a fit according to the disc. It is similar to the hard disk, but in this case, there is a mobile reader head and a motor rotating the disk.
There are recordable and rewritable CD/DVD drives. Rewritable drives allow the disc to be written to multiple times. There is also the opportunity to work with *Double Layer/Single Layer*. Duplex: This refers to replicating the disk on both sides, thus doubling the capacity.
File Systems
Types:
- FAT (File Allocation Table): This system is used by MS-DOS and Windows 95/98. The maximum size of a partition is 2GB, and files are identified with a maximum of 8 characters for the name and 3 for the extension. It is the most widely used, thanks to its support for hard disks. It can have 3 variations: FAT12, FAT16, and FAT32.
- VFAT (Virtual FAT): This corresponds to Windows 95/98 and Windows 2000, allowing the use of long names. It is an extension to the FAT file system and not a system itself. This allows for consistency within the same partition with VFAT. It still has a 2GB capacity limit.
- FAT32: This system handles 32 bits, which allows partitions larger than 2GB. The first OS that implemented it was Windows 95 OSR2. It handles larger clusters, thus increasing disk performance, and supports up to 256 characters in filenames. A disadvantage is that loading a FAT32 system requires more memory compared to FAT16.
- NTFS (New Technology File System): With a structure similar to HPFS, Windows NT is supported by one of Microsoft’s best file systems.
Features:
- Creating historical file data transactions.
- Fail-safe file recovery.
- Control access to information.
- Avoid fragmentation.
Disadvantage: It presents a significant overhead, making it best suited for disks larger than 400MB.