Hard Drive Technology: Understanding Storage, Formatting, and Error Types

Posted on Aug 6, 2024 in Technology

Magnetic Disks, Recording Formats

1. What is a CHS address?

The CHS address represents the coordinates of a specific area on a hard drive, determined by the cylinder, head, and sector.

3. At what time can we decompose the total access time? Indicate typical values of current hard disks.

The total access time can be decomposed into:

  • Search time: The time spent moving the head to the required track. The average value typically does not exceed 10 ms.
  • Latency time: Once the head is on the track, this is the delay in positioning the head over the desired sector. The average value equals the time it takes the drive to rotate to the correct position.

4. How can we reduce the latency?

Latency can be reduced by increasing the rotation speed of the hard drive.

5. What is the “Landing Zone” of a hard drive? What is its utility?

The Landing Zone is a special surface with a rough texture designed to clean dirt that may drag the head. A carbon layer covering the surface acts as a lubricant.

6. What is “prefetching” on a hard drive?

When a data request is received from the interface, the drive accesses the appropriate sectors and stores them in a buffer. It also reads sequentially contiguous sectors to fill the buffer. This reading of additional sectors is called prefetching.

7. Briefly describe the levels of formatting a hard disk.

There are three levels of formatting, depending on the organizational goal:

  1. Level 1: The surface is organized into magnetic domains (areas) that represent bits (a bit is a change in magnetic flux of particles on the surface).
  2. Level 2: The surface is organized into blocks of bits that can be identified. Heads are divided into sectors and tracks. Identification information and error control are added.
  3. Level 3: The disk is organized for use by the operating system. Directories and file allocation tables (FATs) are created.

8. What do you mean by “Seek error” on a hard drive?

A seek error refers to errors during the search process.

9. Classify the types of errors you can find on a hard drive.

Read/Write

  • Misspellings: All units check for typos by verifying the block on the next revolution of the disk.
  • Error reading: Quantified as the errors produced regardless of the number of bits read.

Recoverable/Unrecoverable

  • Unrecoverable errors: The device detects errors but cannot be corrected by ECC or by the number of retries allowed. Specified as errors per bits read. Values can be around 1/1012 and 1/1015, meaning an error for every several trillions of bits read, which is about 350 hours.
  • Undetected errors: Errors not detected by the drive. Usually not specified due to the difficulty of measuring errors that are not detected.
  • Recoverable errors: Retry errors that need to be corrected.
  • Errors: When the arm fails to locate the cylinder, the unit requires the implementation of the recalibration routine to locate the cylinder.

10. What is the MBR of the hard drive? Where is it located physically? What’s in it?

The Master Boot Record (MBR) is a sector that defines the partitions that can divide the disk. It is physically located in the first sector at cylinder 0, head 0, sector 1. It contains the code that loads the BIOS to boot the system using the hard disk.

11. How do 4 parts make up a partition?

  • Boot sector: Contains a routine for operating system boot partition.
  • FAT (File Allocation Table): Contains a list of all fragments (called clusters) that make up any of the files on the volume.
  • Root directory: Contains a list of files on the volume (name, extension, size, etc.).
  • Area information: Contains user information, i.e., files.

12. What is a cluster? What determines its size? Indicate the advantages and disadvantages of a large cluster size.

The cluster is the minimum unit in which files are organized. The cluster size is specified in the boot sector and represents the number of sectors that comprise it. The cluster size depends on the size assigned to the partition.

Advantages of a large cluster size:

  • Less fragmentation.
  • Faster access to files.

Disadvantages of a large cluster size:

  • Wasted space for small files.
  • Less efficient use of disk space.

13. What kinds of hard drives are partitioned? Which of these boots?

All hard drives are partitioned. The partition that contains the operating system boots.

Controls and Disk Interfaces and Maintenance

15. Indicate 3 limitations of the IDE specification.

  • Type of peripheral: They can only connect hard drives.
  • Limited speed with the system: 2 to 3 MB/s (5.5 MB/s with local BUS).
  • Limited cable length: 45 cm.

16. Indicate the improvements of the EIDE specification regarding IDE.

  • Overcomes the size limitation caused by the XT BIOS, allowing drives larger than 504 MB.
  • Higher transfer speeds.
  • Computers come standard with two independent channels (primary and secondary) to connect up to four devices (1 master and 1 slave on each channel).

20. What does the Serial ATA NCQ option include?

The NCQ option allows the drive to run previously sorted commands to minimize arm and head movement, reducing access time.

21. SATA hard drives run at 3 GHz. What is the transfer speed of these disks?

3 * 8 / 10 = 2.4 Gbit/sec

23. What constitutes the SMART technology in a hard drive? Explain its operation.

SMART (Self-Monitoring, Analysis, and Reporting Technology) monitors the variation in the distance between the disk heads and generates a warning message if any issues are detected.

Power Supply

1. Define the following characteristics of a power supply:

  • Hold-up time: The time the power supply maintains output voltage without input voltage, before shutting down.
  • Load regulation: Indicates the power supply’s ability to control the DC output voltage when the load consumption increases or decreases. This ensures that the voltage remains stable even when the load changes.

2. Indicate the following signals used in an ATX power supply:

  • PS_ON: The power-on signal. When this signal is high, the power supply provides power.
  • 5VSB: The output for the standby system. This allows the computer to be turned on via the network, network card, or keyboard.
  • PW_OK: This signal is high when the power supply is operating correctly and the output voltages (+5V, +3.3V) are within the allowed limits.

3. Define the following power problems:

  • Voltage drop: A decrease in voltage levels over a short period of time. This can be caused by connecting large loads (motors, heaters).
  • Blackout: Complete loss of power over a network cycle. This can be caused by events like earthquakes or car accidents.
  • Reset time: A brief loss of power during a network cycle.
  • Peak: A sudden, dramatic increase in voltage.
  • Surge: An increase in voltage for a short period, typically at least 10 ms.
  • Noise: Electromagnetic Interference (EMI) and radio frequency interference (RFI), which distort the expected sine wave of electricity.

4. Make a small drawing or diagram of an on-line UPS (classified as old) and briefly explain its operation.

An on-line UPS operates in two modes:

  • Standby mode: The battery is charging and the power supply feeds the computer.
  • Online mode: The computer is powered by the battery.

5. According to standard EN 50091-3, there are 3 types of UPS. List and explain the operation of one of them. Which one would you choose for a critical server?

The three types of UPS are:

  • Double conversion: This type of UPS provides continuous, clean power to the load. It uses a rectifier to convert AC power to DC power, then an inverter to convert the DC power back to AC power. This provides a clean, stable power source, even during power outages.
  • Line interactive: This type of UPS uses a battery to provide backup power during power outages. It also uses a voltage regulator to smooth out voltage fluctuations. This type of UPS is less expensive than a double conversion UPS, but it does not provide the same level of protection.
  • Standby: This type of UPS only provides backup power during power outages. It does not provide any voltage regulation or filtering. This type of UPS is the least expensive, but it offers the least protection.

For a critical server, I would choose a double conversion UPS because it provides the highest level of protection against power outages and voltage fluctuations.

6. Exercise


Selecting a UPS from the list to protect a classroom of 11 computers available
color printer and are connected to a SWICHT. Use a power factor of 0.75 for
those devices which are not known this. For security should be considered a
oversizing factor of 25%.