Sunday, December 4, 2022

Selectable operating mode SATA (IDE, AHCI, RAID), NVMe


The ideal assembly is when every component of the system works with 100% efficiency. It would seem that such a trivial task as connecting a hard drive to the motherboard should not cause any particular difficulties. We connect the HDD to the appropriate connector, and, voila, there is a place in the system for deploying the operating system and storing files. But not everything is so simple!

In order to know the zen of assembly and get the system that is optimal in terms of certain parameters (speed, reliability, etc.), you need to have a certain understanding of the logic of the operation of modern protocols and data transfer algorithms, knowledge of the operating modes of the HDD controller on the motherboard and skills in the field of their practical use.

BIOS and UEFI – there is a difference!

Before considering SATA operating modes, you should familiarize yourself and consider the differences between BIOS (Basic Input / Output System) and UEFI (Unified Extensible Firmware Interface), because it is with their help that you will have to make changes to the system configuration.

The BIOS is a control program that is “hardwired” into the motherboard chip. It is she who is responsible for the coordinated work of all devices connected to the motherboard.

Starting from 2012-2013, most motherboards are equipped with UEFI, an advanced control program with a graphical interface and mouse support. But, what is called “the old fashioned way”, both options, at the household level, are called BIOS.

Even an inexperienced user understands that the reason for such a radical change of course when creating UEFI was not the desire of manufacturers to “bring” the interface closer to the end user of a PC, to make it more convenient and understandable, but more compelling reasons.

Such a weighty argument was the limitation on the ability to work with large-capacity drives in the original BIOS version. The fact is that the volume of the disk is limited to a value approximately equal to 2.1 TB. It was impossible to take this bar without cardinal changes in the control software. In addition, the BIOS operates in 16-bit mode, using only 1 MB of memory, which in combination leads to a significant slowdown in the process of polling (POST-polling) devices and starting to boot from the MBR area with the “axis” installed.

UEFI is devoid of the above disadvantages. Firstly, the calculated theoretical threshold of the volume of the disk subsystem is 9.4 ZB (1 zettabyte = 1021 bytes ), and secondly, the partition table layout standard (GPT) is used to load the operating system, which significantly speeds up the loading of the operating system.

Partitioning hard drives

As mentioned earlier, the BIOS and UEFI standards have a different approach to hard disk area layout . The BIOS uses the so-called master boot record (MBR), which clearly indicates to the HDD read head the sector from which to start loading the OS.

In UEFI, this is implemented differently. This standard uses information about the physical location of partition tables on the HDD surface.

How it works?

Each hard disk partition is assigned its own unique identifier (GUID) that contains all the necessary information about the partition, which significantly speeds up the work with the drive. In addition, when using GPT, the risk of losing partition data is minimal, since all information is written both in the initial area of ​​\u200b\u200bthe disk and is duplicated at the end, which increases the reliability of the system as a whole.

For understanding – when using MBR, information about the boot area is located only at the beginning of the disk, in a strictly defined sector and is not duplicated in any way, therefore, if it is damaged, it will be impossible to boot the operating system from such a disk. The system will have to be reinstalled.

Another significant difference is that when using the “old” BIOS and MBR, you can create a maximum of four logical partitions on a disk. If you need to create more of them, you will have to take out your shamanic tambourine and resort to certain actions on the verge of magic and “chemistry”. In fact, you have to do the trick with one of the main sections. First, convert it to extended, and then create the required number of additional partitions inside it. In the case of using the GPT standard, all this becomes irrelevant, since initially in Windows, when using the new HDD partitioning philosophy, the user can create 128 logical partitions.

As for the physical partitioning of the disk into logical partitions, here you need to clearly understand the tasks for which they are created. You need to train yourself to clearly separate user data and system files. Based on this, there must be at least two logical drives in the system. One for the operating system, the second for user data.

The best option is to have two physical disks in the PC. SSD 120-240 GB for the system and fast toys and HDD for documents and multimedia files of the required volume.

In some cases, you can also split the user data volume into two partitions. In one store important files (those that need to be saved at any cost) and current ones, the loss of which is not critical and it will be easy to recover them from the Internet (music, movies, etc.). And, of course, accustom yourself to regularly back up the partition with important data (cloud storage, external HDD, etc.) to prevent their loss.

SATA operating modes

Having finished with the necessary theoretical minimum, you should decide on the choice of the mode of operation of the motherboard HDD controller and their areas of application.

IDE is the simplest and hopelessly outdated option, the use of which was relevant n-tsat years ago. It is an emulation of a PATA hard drive. The mode is used when working with outdated hardware or software that requires outdated operating systems. Modern SSDs will not work in this mode!
It is difficult to imagine the need for such an operating mode as part of a modern PC. Unless, at one point in space and time, an old HDD found on the mezzanine with a working OS and “self-woven” exclusive desktop wallpapers converge, and an unbridled desire to save them for posterity.

AHCI is a mode of operation of a modern drive that provides advanced functionality and additional “goodies”. First of all – the possibility of “hot” replacement of hard drives. For a home PC or office machine, this is not very relevant, but in the case of server equipment, this feature will help save a lot of time and nerves for the system administrator. Secondly, the presence of an implemented algorithm for hardware command queuing (NCQ), which significantly speeds up the operation of the drive and the performance of the system as a whole. This is achieved through a competent and optimal algorithm for moving the reading head along the pancake of a classic HDD or more efficient use of memory cells in the case of an SSD drive.

RAID – the ability to organize joint work of several drives in a single disk array . Depending on the tasks, you can combine disks into a highly reliable system (RAID 1), in which information will be duplicated on each of the array disks, or a high-performance system (RAID 0 or RAID 5), when parts of one file are simultaneously written to different disks, significantly reducing while the time of access to the disk array.
NVMe is a completely new standard specifically designed for SSD drives. Because solid-state drives have already “grown” from the SATA-III data transfer protocol, and take new heights in data transfer via the PCI-E interface, while providing the highest speed of read / write operations. At the same time, they are almost twice as fast as their SSD counterparts operating in AHCI mode.
The choice of the operating mode of the drive should be taken responsibly. You must select it before starting the installation of the operating system! Otherwise, when you change it on an already installed OS, there is a very high probability of getting a screen of death (BSOD) and the PC will fail to work.

Of course, you can correct the situation by following a dozen points from the numerous instructions with which the Internet is replete, but it would be more rational to install the OS again, which is called from scratch, than hammering “crutches” in the hope of fixing everything.

When assembling a system, it is important not only to choose the right components and connect wires and cables, it is also important to correctly configure its configuration, because the speed of drives depends not only on the hardware, but also on the way it is controlled.


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