This article offers a detailed introduction about low-level format. And the operating methods are also displayed in this article.

Low-level format refers to dividing cylinders and tracks in blank disk. Then, cylinders are divided into several sectors. Next, each sector is divided into ID, GAP, DATA and so on.

We can see that low-level format is carried out before high-level format. It can not only be achieved in DOS environment, but also in Windows NT systems. Low-level format only support one hard disk rather than a separate partition. When each disk leaves the factory, hard disk manufacturers have performed low-level format on it. Therefore, users don’t need to carry out low-level format.

After reading this post –Check Out This Way To Recover Files From Formatted Hard Drive, you’ll know what low-level format & high-level format are respectively and the way to recover files from a formatted hard drive.

1.Main Principles

Users should pay attention to the fact that under the previous disk reading technical level, low-level format is a deteriorating operation. It has a negative impact on the service life of hard disk.

However, performing low-level format on hard disk, which was produced in recent one or two years, has smaller impact on service life of hard disk, because this doesn’t belong to physical operation.

Many hard disk manufacturers suggest that users try not to perform low-level format. People can re-divide sectors by low-level format when large numbers of bad sectors appear, because hard disk has been used for a long time or is affected by external strong magnetic and magnetic field. But the premise is that hard disk isn’t physically damaged.

Function of low-level format to HDD: low-level format to HDD is a way to thoroughly initialize disk. Data previously saved on hard disk will be lost after low-level format. So, in general, we had better avoid performing HDD low-level format if it’s not very necessary to do so.

But, there are two situations in which we have to carry out low-level format. One is that hard disk manufacturers will perform low-level format to disk before it leaves the factory. The other is that when hard disk has bad sectors, performing low-level format to it can reduce spreading speed of bad sectors or shield bad sectors.

In the first case, we don’t need to describe in details, because HDD low-level format before it leaves factory only comes into contact with disk engineers. For average users, there is no need to consider this matter. In the second case, what type of bed sectors need low-level format? Let’s take a look at types of hard disk bad sectors before describing this critical question.

2.Cause and Effect

Logical Bad Sector

In general, bad sectors are divided into physical bad sectors and logical bad sectors.

Logical bad sectors are easier to deal with than physical bad sectors. It refers to that hard disk is interfered when data are written in it. This causes ECC errors. From the perspective of process, it refers to when data are written in hard disk, it will use ECC logic to re-combine data. Generally, 512 bytes need to be written in OS. But actually, additional dozens of bytes will be written in hard disk. And all these bytes will be verified and encoded by using ECC. If ECC correction code calculated by original bytes is different from that calculated by read-out bytes, this will cause ECC error. This is called the cause of logical bad sectors.

The CHKDSK command is able to check the disk surface for bad sectors and mark them. But what if CHKDSK deletes your important data? You are advised to use MiniTool Power Data Recovery to recover data after CHKDSK.

Physical Bad Sector

For physical bad sectors, it has catastrophic damage to hard drive. It can be divided into internal and external physical bad sectors. Physical damage of hard disk surface belongs to external physical bad sectors. This can’t be repaired.

But when outside influence causes data writing error, OS will judge this as physical bad sector. Physical bad sectors can be repaired with hard disk tools (hard disk check and repair software provided by disk manufacturers). In addition, for tiny hard disk surface damage, some hard disk tools (such as Data Lifeguard Tools of Western Digital) can fix errors by re-directing to a good sector.

Tip: Don’t know the disk status? Just try MiniTool Partition Wizard to check whether your hard drive has some physical bad sectors or not with “Surface Test” feature.

For these types of bad sectors, external physical bad sectors are certainly beyond repair. It’s a most direct damage to hard disk surface, so, it can’t be repaired even if you perform low-level format or use hard disk tools (unless it’s a minor damage, some tools can solve this problem by retaining these bad sectors).

Low-level Format Effect

(1) Hard Disk Bad Sectors and Low-level Format

In the case of logical bad sectors or soft physical bad sectors on hard disk, logical bad sectors can be automatically repaired during low-level format while internal physical bad sectors are shielded ( hidden ). Carrying out low-level format on hard disk can delete all disk partitions, but bad sectors still exist. Shielding bad sectors is only to hide them in order to make users not use these bad sectors when they store data. This can ensure data reliability of users to a certain extent, but bad sectors will spread along with the growing number of hard disk partition and format.

So we don’t advise users to perform low-level format. If the bad hard disk is in the warranty period, it’s better to repair it or find the dealer to get a new one. This is not only the best solution, but also a complete solution. If hard disk is beyond warranty period, you can try low-level format to avoid data loss caused by storing them on bad sectors.

(2) Computer Virus and Hard Disk Low-level Format

When a large number of viruses attack a certain sector of hard disk, it’s difficult to kill them by general format. This can be reflected when normal computer working interface can’t be entered. And no matter how you format system disk or reinstall OS, the system can’t work properly after being reinstalled.

Some virus file systems use the coding method of prefix and suffix encryption, so it’s difficult to kill virus by general format, that’s to say, after encrypting prefix and suffix codes of virus files, this disk sector is prevented from being generally formatted. Ordinary computer users are unclear about this, so they always think there are problems with computer. They don’t know what storage area is attacked by virus.

If the above phenomenon appears, we can only carry out HDD low-level format. The so-called computer low-level format is to perform high-intensity magnetic on magnetic recording tracks ( tracks ) of disk sector. Virus files stored in disk sector can be eliminated in this way. You can format partition and reinstall OS after low-level format. And now, computer can work properly. Format low-level format command in DOS command of system disk is usually used to achieve HDD low-level format. This is also called computer DOS system format.

Now, we’d like to introduce a most popular computer virus eliminating method, which can basically clear all computer virus. It’s also a virus eliminating method when computer is in safe mode state. When computer works in safe mode state, virus files usually show a non-operational state. It’s difficult for us to eliminate computer virus files which are being copied, but we can eliminate intractable virus by using anti-virus software when the virus is in non-operational state.

We can press F8 when start computer to enter running option interface. Then we use UP key and Down key to choose safe mode and press Enter. Next, we can use downloaded anti-virus software to kill virus. Computer will automatically restart to work in normal state after finishing killing virus. If computer intractable virus can’t be killed by above method, you can only choose to perform low-level format to hard disk.

3.Operating Method

Low-level Format Tools

For how to carry out HDD low-level format, generally we can use low-level format tools. This will be described in detail in the following sections.

Here we’d like to mention some related topics. Low-level format tool is essentially different from HDD testing tool. Low-level format tool can achieve low level format to hard disk while HDD testing tool introduced by disk manufacturers is used to test disk. It can detect hard disk errors and remind users to back up data or repair hard disk. It can’t be used to perform low level format to HDD. We usually use some software to perform low-level format on hard disk. Common tools for low-level format include Iformat, DM, disk tools introduced by hard drive manufacturers and so on.

Low-level Format Assembly Language
Debug assembly language is used to perform low-level format.

Low level format to hard disk can completely damage data on hard disk. So, we have to be careful before we do this operation.

There are many ways to achieve low-level format. For instance, we can carry out low level format to hard disk directly in CMOS or we can use assembly language to achieve this. Assembly language is a low-level programming language. It is more flexible than DM and other tools. Its specific application is to use debug process. The operation is to call the low-level format program ( this low-level format program is also used when you directly perform low-level format to disk in CMOS ) in BIOS in debug environment. Implementing method usually includes the following three types:

(1) We can directly call low-level format program in BIOS, ROM

The low-level format program is always stored in BIOS, ROM of many computers. The storing address begins with C8005H address. And specific operations are as follows:

A: \>Debug

-G C800: 0005 (then the screen displays information, which may be different in different versions of the BIOS and then the prompt appears after pressing Enter:)

Current Interleave is 3, select new interleave or Return for current ( which is to ask users to select cross-factor; users can press Enter to indicate the default value 3; you can also enter a new cross-factor value; hard drive cross-factor is generally 3, so you may directly press Enter; then screen prompts : )

Press “Y” to begin formatting the drive C: with interleave 03 (you may start low-level format on hard disk after typing “Y”)

Formatting … (it will ask whether you deal with bad track or not after completion)

Do you want to format bad track-answer YN?

If you don’t want to format, then you can use “N” to answer. The screen displays:

Format Successful, system will new restart, Insert Dos diskette in drive A:

After inserting system disk into drive A, you can perform partitioning, advanced formatting and other operations to install the system.

(2) Low-level hard disk format can be achieved by calling interrupted number 7 feature in INT, 13H.

Operations are as follows:


-A 100

-XXXX: 0100 MOV AX, 0703; (crossover factor is 3)

-XXXX: 0103 MOV CX, 0001; (start with track 0 and sector 1)

-XXXX: 0106 MOV DX, 0080; (track 0 of disk C)

-XXXX: 0109 INT 13

-XXXX: 010B INT 3

-XXXX: 010D

-G 100

So, hard disk has achieved low-level format.

(3) Low-level hard disk format can be achieved by calling interrupted number 5 feature in INT, 13H.

You can only choose to achieve low-level format on cylinder 0, track 0 and sector 1 rather than achieve low-level format on entire disk when call interrupted number 5 feature in INT, 13H to hard disk. This can makes low-level format complete within a short time. Specific operations are as follows:


-A 100

-XXXX: 0100 MOV AX, 0500; (calls number 5 feature)

-XXXX: 0103 MOV BX, 0180; (set buffer address)

-XXXX: 0106 MOV CX, 0001; (start with track0 and sector1)

-XXXX: 0109 MOV DX, 0080; (track 0 of disk C)

-XXXX: 010B INT 13

-XXXX: 010D INT 3

-E 0180, 0, 0, 0002; (write in parameter)

-G 100

Formatting Method

Performing Low-level Format with DM

The full name of DM is Hard Disk Management Program. It can achieve some management like low-level format and check on hard disk. This can improve the hard disk usage efficiency. All in all, DM has the following functions: low-level format to hard disk, partitioning, high-level format, setting disk parameters and other functions.

In practical applications, DM is the same as DOS command (such as fdisk or format). Its command format is: ADM (parameters), wherein the parameters can take the following values:

M, DM software can be entered manually. If the parameter doesn’t exist, DM will run in automatic mode. It will implement INITIALIZE, PARTITIONG and PREPARAFION one by one.

C, DM software runs on the color display.

P, DM software manages hard drives by PCXT.

A, DM software manages hard drives by PCAT.

Runs by 2, DOS, 2.XX version mode.

Runs by 3, DOS, 3.XX version mode.

Runs by 4, DOS, 4.XX version mode (only DM 5.01 version has this parameter).

V, DM runs by using the mode of changeable cluster length and root directory entry.

DM can usually be started with the following two methods:

(1) ADM, automatic mode ( when hard disk is initialized, many parameters are set by default without human intervention )

(2) ADM, manual mode (when hard disk is initialized, some parameters need manually specifying)

After start DM, users can choose appropriate operations according to their demands. Because its interface is the same as that of DOS, it’s quite simple to use.

When performing formatting operation in Windows, do you fail to do this job? If you receive some errors, for example,

Windows was unable to complete the format or the format did not complete successfully, just try MiniTool Partition Wizard to format your disk.

Other Methods In addition to the above introduced low-level format tools, there are many other low-level format methods.

(1) Direct Operation in CMOS

If it can be supported by BIOS, users can perform low-level format to hard disk in CMOS. This is a very easy and convenient way to achieve low-level format. Therefore, if it is possible, we’d like to recommend this way to perform low-level format to hard disk.

Specific operating method: you can enter CMOS Setup (if BIOS belongs to Award, system will prompt entering CMOS Setup by pressing DEL; if BIOS belongs to Intel, generally you can press F2 to enter CMOS Setup) according to system prompt when start computer. Then you may choose “low formatted Hard Disk Drive” in CMOS menu. Finally, you can make hard disk wait for low-level format according to the prompt of program. At the same time, you may answer some program questions before performing low-level format to hard disk.

(2) Low-level Format to Hard Disk with Iformat Program

In addition to DM tool, there is another common low-level format program, Iformat.exe. It is a low-level format tool for hard disk and introduced by Maxtor. After running Iformat.exe in DOS mode, system will launch warning interface. The content in the interface shows that when users use this tool, all data on hard disk will be lost. So, users are recommended to backup data before running this tool. And at the same time, users are advised to move other disks away. If users forget to back up data and they want to exit this program, they can press any key except ” Y “. If users are sure to carry out low-level format to hard disk, they can press ” Y “.

The program will ask users to select hard disk or perform low-format to the current disk after users choose “Y”. Then, users will answer some questions to start HDD low-level format.

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