Why is the actual capacity of the hard disk always smaller than the nominal capacity?

Regarding this issue, Xiao Er has already been in the last issue, but there are more friends who write to ask, so I will repeat it here. The main reason why the actual capacity of the hard drive is less than its nominal capacity is that manufacturers generally calculate the capacity by 1000K bytes per megabyte, while the BIOS and test software of most motherboards are calculated at 1024K as one megabyte. As a result, there is a difference between the two.

The capacity of the hard disk is divided into the physical disk capacity calculated purely by the number of heads, the number of cylinders and other physical parameters, and the actual available space after partitioning, formatting and other operations. In addition, selecting different working modes (normal, LBA, large) in the CMOS may also cause capacity inconsistencies. So this is just a matter of calculation method, not profiteers.

The target capacity of the hard disk is at the level of 1000, that is, 1g = 1000m, 1m = 1000b but the computer is actually binary, 1g = 2 10 (2 to the 10th power) = 1024m 1m = 1024b

The total number of bytes (b) is the same, for example, if a hard disk marked as 120G is actually 120*1000*1000 (1024*1024).

At the same time, it is not that the 120G hard disk can be full of 120G, just like when installing the software, the software that occupies 100M space after installation needs to be more than 100M installation space.

1. This is a normal phenomenon.

g = 1024 * 1024 * 1024 bytes, but the hard disk manufacturer regards 1000 * 1000 * 1000 bytes as 1g when producing, so there is a difference.

3. At present, the actual capacity of 80G is about 74G, and 120G is about 111G, which means that the actual capacity is 92%-94% of the nominal capacity.

4. The hard disk needs to be partitioned and formatted, there are differences between the operating systems, coupled with the behavior of copying files when installing the operating system, the hard disk will occupy more space, so there will be a difference between the hard disk capacity and the nominal capacity displayed in the operating system, and the difference between the two types of hard disk capacity should be about 5%-10%.

Because in the world of computers, the unit conversion is calculated according to 1024, 1024b = 1kb, 1024kb = 1m, 1024m = 1g

However, when the hard disk manufacturer calculates the capacity, the unit conversion is calculated according to 1000. 1000b = 1kb, 1000kb = 1m, 1000m = 1g and so on.

Therefore, the capacity of the nominal 512g solid state is actually 512*1000*1000*1000=.

And the algorithm of the computer, it is displayed.

The nominal 500g solid-state is the only one.

If you are a 1T hard disk, then the conversion from G to T depends on whether it is 1024 or 1000, and the actual capacity is also different.

According to 1024g=1t, then the actual capacity is; According to 1000g = 1t, it is actually 931g

In addition, after installing the system, it will divide the boot partition and the recovery partition, which is invisible when this part of the space is in "This PC". Therefore, the total number of hard disks seen in "This Computer" is one or two gigabytes smaller

Your hard drive is filial piety 500g, nor is it 512g.

This is actually due to the fact that the conversion criteria adopted are different.

The computer world's 1024 = 1K conversion algorithm is the standard of the International Electrotechnical Commission (IEC), and 1000 = 1K is the base system in the metric (SI) unit.

In the IEC standard, there is no such unit as "KB", "MB", and "GB", but units such as "KIB", "MIB", and "Gib", and all units have an extra letter "i" in the middle of the SI standard.

So in reality, it's 1024kib = 1mib and 1024mib = 1gib instead of 1024kb = 1m and 1024m = 1g

The computer world follows the IEC standard, while the manufacturer uses the SI standard.

In official language, the two standards cannot be confused, and units such as "mb" in Qiaoshan manuscripts without "i" are metric units, which must be 1000 decimal system.

Therefore, the hard disk manufacturer uses 512GB and 1000GB computing capacity in metric units, but the computer displays the capacity in IEC units of 476GB and 931GB, resulting in the actual capacity of this hard disk is smaller than the nominal capacity.

The reason for this is that about 20 years ago, the translators who introduced these units were not computer majors, and confused IEC units with "I" with metric units without "I". In our colloquial language, Gib becomes GB

Because computers are binary, the operating system calculates the hard disk capacity in 1024 increments, while the hard disk manufacturers use every 1000 in terms of computing capacity.

At present, the mainstream hard disk capacity is 250G, 320G, 500G, 1TB, etc., according to this operation rule, to calculate the correspondence between the labeled capacity of the commonly used hard disk and the real whole disk capacity.

Each hard drive will make a defect mapping table based on the test results, and lock these areas to prohibit access, unless you use professional tools to access these defective areas.

You actually see that the continuous space is only logically continuous, and it may not be continuous inside the hard disk, which means that the hard disk you get has actually been processed by the manufacturer.

If the partitioned cluster area (data area) is not an integer multiple of the cluster size, the sector space of less than one cluster will be left free unless it is diverted for other purposes.

The hidden partition of ordinary brand machines is also not displayed by default on the operating system, so it also takes up space. There are also certain special encrypted partitions.

The actual capacity of the hard drive is smaller than the nominal capacity due to the different storage units used by the hard drive manufacturer and the computer system, as well as the loss of storage space due to the formatting and partitioning process of the hard drive.

Hard drive manufacturers typically use "base decimal" computer storage capacity, where 1GB equals 1 billion bytes and 1TB equals 1 megabyte, while computer systems use "binary" computer storage capacity, where 1GB equals 2 to the 30th power and 1TB equals 2 to the 40th power byte. Because of this different unit of measurement for computer storage, the nominal capacity of the hard drive manufacturer is actually about 7 to 10 percent more than the capacity recognized by the computer system.

In addition, the formatting and partitioning process of the hard drive can also lead to loss of storage space. During formatting, the file system creates a file system table on the hard disk to track data allocation, which requires a certain amount of storage space. During the partitioning process, part of the storage space is also reserved for backup and system files, resulting in a reduction in storage space.

Therefore, when a computer system displays the capacity of a hard drive, it usually shows a little less actual capacity than the capacity advertised by the hard drive manufacturer. Although this difference may be confusing for some consumers, this situation is widespread, not just for hard drives, but also for other storage devices.

In order to better understand the storage space of a hard drive, it is recommended to carefully review the specifications provided by the manufacturer and understand the computer storage unit of measurement used before purchasing a hard drive. When managing hard disk space, using some tools and techniques for hard disk space, such as formatting and partitioning tools, can give you more control over the storage space of your hard drive to better meet the storage needs of users. <>

Recently, a customer asked me such a question:

Why did I buy a new 1TB SSDThe total recognizable capacity is only 932GBThis?

Because ......

I believe that many careful friends have found that after the newly purchased SSD is installed in the computer, the actual recognition capacity does not reach the nominal level.

Why is that? This is a few dozen gigabytesThe capacity of the poor in, isn't it a big loss for consumers?

Actually, it's all because of ......

Some capacity is reserved for OPspace

Then the question arises again, what is OP space? What can OP Space do? In order to solve everyone's questions at one time, let's talk about those things in the OP space today.

What is OP?

OP is the internal preset mechanism of the SSD, the full name is over provisioning, and the Chinese name is "reserved space". It refers to the user's inoperable capacity, which is the actual capacity of the SSD minus the user's available capacity, which is the hidden space that really exists in the SSD but is not operated by the user.

What is OP for?

It is generally used for optimization operations: such as WL (Wear Balance), GC (Garbage**), Bad Block Mapping, etc. The OP space can reduce the number of reads and writes of NAND flash memory and increase the service life.

To put it simply, we can understand the OP space as the private territory of the SSD master, which is used to offset the various damage caused by daily use of the SSD, and many optimization algorithms are also based on this.

What is the structure of the OP?

OP is generally divided into three layers:

l Tier 1: It is generated due to different unit conversions, accounting for about the nominal capacity of the SSD, and this part of the space is used for OP by default;

l Layer 2: The existence and capacity of OP depend on the manufacturer's settings. SSD manufacturers will set it according to their own flash memory particle quality, warranty period, or market positioning, and the larger the second-layer OP space, the stronger the comprehensive performance of the solid state;

l Layer 3: Users can manually set OP in daily use, and the function is similar to that of Layer 2.

At this point, I think you must also understand the definition and role of OP space, and finally let's draw the key points again-

OP space, we can understand it as a cache, and the empty blocks provided by OP space help NAND flash to maintain an effective wear balance, garbage**. Therefore, the role of OP reserved space for SSDs is very large, and it is not that manufacturers are short of capacity or two.

Easter egg time: If you look at the previous article, you must have found that I mentioned that users can manually set OP, so how to operate? That's where our Samsung Magician SSD management software comes in!

Open the Samsung Magician software and click "Over Provisioning" at the bottom right"It's ready to go! The maximum can be set to 50%, but Xiaoxing recommends that you set 10%, after all, the capacity of SSDs is bought with money.