Character device Vs Block device
 

Dear all,

I added 20gb space to linux machine from d:\ -->(host)

Raw partitions are unformatted disk partitions; -because( ntfs cannot recongnized by ext3)

I read Raw devices are character devices.
Terminals operate in character mode.

The first entry in the permission field indicates either b--> block, or c--> character

/dev/sdb - This is a raw partition

Then why Linux shows /dev/sdb as 'BLOCK DEVICE'
It must start with c (character device)

Thanks in advance.

Simple explantion wolud be better to get better idea.
From my previous post i got very big explantions.
For me it was NOT easy to understand.

A Character device is a terminal, VDU, keyboard, serial connection as data is transferred one character at a time. There are various handshake signals to inform the sender that the character has been received, etc. The processor generally handles all the transfer handshaking.

A Block device; hard disk (includes pendrives), tape drive, CD/DVDs reads and writes data as "blocks" of data rather than one character at a time, they also tend to do this without use of the processor which is only used to initiate the transfer by DMA (Direct Memory Access) The protocol for block transfer needs to know where the data starts and it's length which means there is a much lower processor overhead.

My :twocents:

Play Bonny!

:hattip:

That is simply wrong. Disks are block devices. They are addressed and accessed in blocks.

What problem are you actually having.

Originally Posted by Joy Stick

I read Raw devices are character devices.

Raw devices are character devices (i found via Google)

REF_LINKS:

Unformatted disk partitions are called 'RAW DEVICES'
All unpartitioned devices are Raw devices.

Then why Linux shows /dev/sdb as 'BLOCK DEVICE'

Thanks

No, that has nothing to do with it. It's unformatted because VMWare doesn't format the "disk" for you, that's up to the VM. The filesystem used on the host is irrelevant, the guest never sees the host's filesystem, that's the point of virtualization.

A disk that contains an unsupported filesystem will look VERY different from one that is not partitioned/formatted at all. You're looking at the output for an unformatted disk, not an unsupported filesystem.

You have an unpartitioned, unformatted disk (block device), not a "raw device". Some people might call it "raw" because it's untouched, similar to "raw" meat that hasn't been cooked, but it's not the same thing as the "raw device" being referenced in those links.

A raw device i.e. /dev/raw* is not the same thing as /dev/sdx or an unpartitioned or unallocated space on a hard drive. As you have discovered it is typically used to perform raw I/O on a block device and bypass caching like Oracle

https://en.wikipedia.org/wiki/Raw_device

regardless of a drive being formatted or unformatted has nothing to do with its device type.

The link that michaelk posted shows a very good example of what a raw device is. Its basiclly a device that is exposed to the user without much OS implementation.

A extremely simple explanation is below, as you asked for.

These first two are setup and managed by the Operating System.
Character device - device communicates via character exchange.
Block Device - Device communicates via blocks of data.

Raw device - Device is not managed by the OS to communicate. ( gives you raw access )