Microsoft talks about Windows 8 supporting large-capacity hard drives, 4KB sectors

Although the hard disk storage technology is getting slower and slower, the increase in capacity is unstoppable. IDC recently predicted that the capacity of a single hard drive will reach 8TB in 2015 (2TB for single-disc capacity), which is more than twice the current size.

Because of hardware and software design flaws, large-capacity hard drives have caused trouble many times in history. Recently, the hard disk capacity problem appeared on 2.2TB, so when developing Windows 8, Microsoft fully considered The full support issue for large capacity hard drives, as well as the new 4KB sector format. The method of addressing hard

addressing method used was initially the hard cylinder /head /sector (the CHS), is determined by a data specified cylinder, head, sector, respectively The exact location of the block, but this method fails in the face of a 137GB capacity hard drive.

Instead of logical block addressing (LBA), discrete geometry is no longer used to specify sectors, but sector numbers are used to represent specific blocks of data. Each sector has a predefined size (previously 512 bytes), numbered sequentially starting from 0, and the maximum is the total capacity divided by the sector size.

Disk Partitioning Mechanism

The LBA addressing method theoretically supports very large hard disk capacities, but in reality the number of sectors is also subject to the disk partitioning mechanism.

The concept of disk partitioning dates back to the early 1980s when system administrators invented data for the convenience of using different file systems. The Master Boot Record (MBR) partition table supports up to 32-bit information, which is converted to a number of bytes of 2 to the 32nd power, which is about 2.2TB.

You may despise their "short-sightedness", but in the eyes of people 30 years ago, 2.2TB is almost an unreachable astronomical number, knowing that the largest civilian hard drive at the time was 5MB, and the price is over $1,500.

In fact, just in the 1990s, people have realized the 2.2TB capacity limitation problem. For this reason, many companies have jointly developed a flexible partitioning mechanism. This is the GUID partition table, referred to as GPT. And as part of the UEFI (Unified Extensible Firmware Interface) specification. GPT supports up to 64-bit information, and the theoretical maximum capacity is 9.4ZB, which is equivalent to 9400000000TB. It is also an "astronomical number", but maybe one day it will become the second "2.2TB".

Starting with Windows Vista 64-bit, Microsoft supports booting from a GPT partitioned hard drive, but requires the motherboard firmware to be UEFI, not a legacy BIOS.

Firmware in PC: BIOS, UEFI

The meaning of BIOS stands for its purpose: basic input and output system. It appeared when the PC was invented 30 years ago, but it is still the same today. UEFI is used to replace the BIOS, but it has not been put into practical use for a long time, until the latest Intel and AMD platforms began to spread.

UEFI has considered the support of GUID partitions for super-capacity hard drives since its inception, which is much more reliable than the way of bypassing the BIOS. Beginning with Windows 8, Microsoft will fully support UEFI support, and manage large hard drives with UEFI firmware, GTP partition table, and LBA addressing methods.

Below is the way to install and start the operating system on the 3TB hard disk through the above method.
4KB Sector Format

All hard drives have some form of error correction information and logic built in to automatically handle the signal-to-noise ratio (SNR) when reading disk discs. As the capacity of the hard disk increases, the data storage bit gets closer and closer, and the SNR decreases. Each sector of the hard disk has to store more ECC (error check code) to compensate for the read error. The narrow sector space of bytes is slowly not enough.

So, the hard disk manufacturer has expanded the sector capacity to 4KB, called "advanced format" (AF), and used the new ECC encoding mechanism to correct errors more efficiently, accounting for storage. There is also less space, which is equivalent to expanding the available capacity. At present, Western Digital, Seagate and other hard disk manufacturers have gradually popularized the 4KB sector format.

The sector size is increased to 4KB, and the data update must be based on this size, so in order to achieve logical addressing of smaller blocks, the hard disk must do some extra work.

As shown above, a 4KB physical sector can still be divided into 512-byte logical sectors for logical addressing. In order to write a single 512-byte logical sector, the hard disk cannot simply write the head to the 4 KB physical sector. Instead, the data in the entire physical sector needs to be read into the cache. Modify the corresponding 512-byte logical sector, and then write back as a whole to overwrite the old sector. This is called "Read-Modify-Write".

A hard disk with this intermediate conversion layer is called "4K with 512-byte emulation", abbreviated as 512e, and no one is called "4K Native", that is, one is analog and the other is native.

Read-modify-write can affect actual performance when faced with large amounts of inconsistent data, because Windows must ensure that the application can extract the entire 4KB physical sector, and the application needs to ensure I/The consistency of O to report the physical sector size.

After learning the previous version of the advanced format, Windows 8 will be the key design point, and will be the first operating system to fully support 512e and 4K Native formats, including :

- Enhance existing APIs and introduce new APIs to make it easier for applications to query the physical sector size of hard disks;

- Enhance large-capacity sector identification of NTFS file systems, This includes ensuring the appropriate subsequent sectors when writing extended writes (when writing to the end of the file);

- The new file format of Hyper-V virtualization technology VHDx can also identify large sectors, complete Support for both formats;

- Enhance Windows boot code to ensure proper booting on 4K Native native hard drives.

There is more work going on in Windows 8 silently.