How important is it to format before installing?

I clean install will normally have less processes running because you haven't installed or downloaded nearly as much. Be happy about it. I would be.

The importance of reformatting will be partially opinion based. It definitely helps get things optimized for the reinstall and is always recommended. Some will say don't worry about it, and others will say to format and install again. Personally, I think the slow down you see it mostly you looking for something to be wrong since you're obviously concerned about the fact you didn't format first. Whatever you do is up to you. If you think something is wrong and you want to reformat, here is a helpful guide:
SSD / HDD : Optimize for Windows Reinstallation

I agee. Its typically user preference.

For SSDs though, I would say a Sanitary Erase or HDD Erase (depending what type you have) should be done before reinstalling.
SSDs work slightly different, so just reinstalling without erasing the drive can hinder performance afterwards somewhat.


However, for a spinning drive, it shouldnt make that much of a difference.
AS Petey7 said, its still a clean instal of Windows.

None-the-less, I would recommend running a clean cmd from cmd prompt at instal screen, then a quick format 1st. (again personal preference)
It should be more than suffecient and only takes about a minute.

AstaLaVista said:

I thought you couldn't install an OS on an Un-Formatted drive? is that not the case?

The only drives that aren't formatted in some way are brand new ones. He meant reformat. As in, pick the format option.

I think it is : Format C:\ /q
But here is the whole command:

C:\Windows\system32>format /?
Formats a disk for use with Windows.
FORMAT volume [/FS:file-system] [/V:label] [/Q] [/A:size] [/C] [/X] [/P:passes] [/S:state]
FORMAT volume [/V:label] [/Q] [/F:size] [/P:passes]
FORMAT volume [/V:label] [/Q] [/T:tracks /N:sectors] [/P:passes]
FORMAT volume [/V:label] [/Q] [/P:passes]
FORMAT volume [/Q]
volume Specifies the drive letter (followed by a colon),
mount point, or volume name.
/FS:filesystem Specifies the type of the file system (FAT, FAT32, exFAT, NTFS,
or UDF).
/V:label Specifies the volume label.
/Q Performs a quick format. Note that this switch overrides /P.
/C NTFS only: Files created on the new volume will be compressed
by default.
/X Forces the volume to dismount first if necessary. All opened
handles to the volume would no longer be valid.
/R:revision UDF only: Forces the format to a specific UDF version
(1.02, 1.50, 2.00, 2.01, 2.50). The default
revision is 2.01.
/D UDF 2.50 only: Metadata will be duplicated.
/A:size Overrides the default allocation unit size. Default settings
are strongly recommended for general use.
NTFS supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K.
FAT supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,
(128K, 256K for sector size > 512 bytes).
FAT32 supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,
(128K, 256K for sector size > 512 bytes).
exFAT supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,
128K, 256K, 512K, 1M, 2M, 4M, 8M, 16M, 32M.
Note that the FAT and FAT32 files systems impose the
following restrictions on the number of clusters on a volume:
FAT: Number of clusters <= 65526
FAT32: 65526 < Number of clusters < 4177918
Format will immediately stop processing if it decides that
the above requirements cannot be met using the specified
cluster size.
NTFS compression is not supported for allocation unit sizes
above 4096.
/F:size Specifies the size of the floppy disk to format (1.44)
/T:tracks Specifies the number of tracks per disk side.
/N:sectors Specifies the number of sectors per track.
/P:passes Zero every sector on the volume passes times. This switch is
not valid with /Q
/S:state Where "state" is either "enable" or "disable"
Short names are enabled by default

The clean cmd wipes the partition table from the HD.

When you boot from your Win7 DVD, at the very 1st instascreen press CTRL+F10

it brings up a cmd prompt.
To find out the number assigned to your disks,
type: diskpart
then when loaded type: list disk
This will give you a list of all HDs, and what number is assigned to each.

if you only have 1 HD, it will be disk 0.

then type: select disk (the number of disk you want)
So for disk 0 it would be : select disk 0

then type clean

it will wipe the entire drive and ALL partitions

type exit and proceed with instal as normal.
if you want to create your partions (or juast one single one)and do a quick format, you can at the next screen.
But if not mistaken, 7 will do a quick format on its own at this stage as the HD is just 1 huge unallocated space now.

Now if you wish to create a partition and format in the cmd promp, after you do the clean cmd, the cmds are as follows:
select disk (whatever #)
clean
create partition primary
active
formatfs=ntfs quick
exit

this will clean the drive and do a quick format as 1 large partition. but, as already stated, you can do the format and partition creating in the setup outside of cmd prompt if its easier for you.

The more advanced options whs already listed.