Why is the transfer unit of block devices block not page?
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Operating System Concepts says
A character-stream device transfers bytes one by one, whereas a block device transfers a block of bytes as a unit.
But I heard that the unit of transfer between main memory and disk is page.
Between what and what do the "transfers" in the quote happen?
Why is its transfer unit not page but block or byte?
Thanks.
memory block-device character-device
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up vote
-2
down vote
favorite
Operating System Concepts says
A character-stream device transfers bytes one by one, whereas a block device transfers a block of bytes as a unit.
But I heard that the unit of transfer between main memory and disk is page.
Between what and what do the "transfers" in the quote happen?
Why is its transfer unit not page but block or byte?
Thanks.
memory block-device character-device
Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12
add a comment |Â
up vote
-2
down vote
favorite
up vote
-2
down vote
favorite
Operating System Concepts says
A character-stream device transfers bytes one by one, whereas a block device transfers a block of bytes as a unit.
But I heard that the unit of transfer between main memory and disk is page.
Between what and what do the "transfers" in the quote happen?
Why is its transfer unit not page but block or byte?
Thanks.
memory block-device character-device
Operating System Concepts says
A character-stream device transfers bytes one by one, whereas a block device transfers a block of bytes as a unit.
But I heard that the unit of transfer between main memory and disk is page.
Between what and what do the "transfers" in the quote happen?
Why is its transfer unit not page but block or byte?
Thanks.
memory block-device character-device
memory block-device character-device
asked Oct 4 at 0:57
Tim
23.9k67232418
23.9k67232418
Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12
add a comment |Â
Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12
Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12
Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12
add a comment |Â
1 Answer
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The transfers typically occur between the storage device and main memory. When you hear about pages when referring to disk, they're probably talking about virtual memory which is in terms of pages since that's the unit of storage the MMU deals with. But block devices relate to all sorts of devices that may or may not be disks so you have this separate concept of a blocks and block size. Disk block size and memory page size used to (generally) be the same, 4096 bytes, which of course was very convenient. But there's nothing that says they must be the same. For example, you might have a multi-terabyte disk used to store images where it makes sense to increase the block size to 32k or more... having no impact on memory page size. Generally, as long as one is a power of two multiple of the other it can be made to work without too much trouble.
New contributor
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
accepted
The transfers typically occur between the storage device and main memory. When you hear about pages when referring to disk, they're probably talking about virtual memory which is in terms of pages since that's the unit of storage the MMU deals with. But block devices relate to all sorts of devices that may or may not be disks so you have this separate concept of a blocks and block size. Disk block size and memory page size used to (generally) be the same, 4096 bytes, which of course was very convenient. But there's nothing that says they must be the same. For example, you might have a multi-terabyte disk used to store images where it makes sense to increase the block size to 32k or more... having no impact on memory page size. Generally, as long as one is a power of two multiple of the other it can be made to work without too much trouble.
New contributor
add a comment |Â
up vote
1
down vote
accepted
The transfers typically occur between the storage device and main memory. When you hear about pages when referring to disk, they're probably talking about virtual memory which is in terms of pages since that's the unit of storage the MMU deals with. But block devices relate to all sorts of devices that may or may not be disks so you have this separate concept of a blocks and block size. Disk block size and memory page size used to (generally) be the same, 4096 bytes, which of course was very convenient. But there's nothing that says they must be the same. For example, you might have a multi-terabyte disk used to store images where it makes sense to increase the block size to 32k or more... having no impact on memory page size. Generally, as long as one is a power of two multiple of the other it can be made to work without too much trouble.
New contributor
add a comment |Â
up vote
1
down vote
accepted
up vote
1
down vote
accepted
The transfers typically occur between the storage device and main memory. When you hear about pages when referring to disk, they're probably talking about virtual memory which is in terms of pages since that's the unit of storage the MMU deals with. But block devices relate to all sorts of devices that may or may not be disks so you have this separate concept of a blocks and block size. Disk block size and memory page size used to (generally) be the same, 4096 bytes, which of course was very convenient. But there's nothing that says they must be the same. For example, you might have a multi-terabyte disk used to store images where it makes sense to increase the block size to 32k or more... having no impact on memory page size. Generally, as long as one is a power of two multiple of the other it can be made to work without too much trouble.
New contributor
The transfers typically occur between the storage device and main memory. When you hear about pages when referring to disk, they're probably talking about virtual memory which is in terms of pages since that's the unit of storage the MMU deals with. But block devices relate to all sorts of devices that may or may not be disks so you have this separate concept of a blocks and block size. Disk block size and memory page size used to (generally) be the same, 4096 bytes, which of course was very convenient. But there's nothing that says they must be the same. For example, you might have a multi-terabyte disk used to store images where it makes sense to increase the block size to 32k or more... having no impact on memory page size. Generally, as long as one is a power of two multiple of the other it can be made to work without too much trouble.
New contributor
edited Oct 4 at 4:57
New contributor
answered Oct 4 at 4:37
blihp
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New contributor
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Thanks. Why is its transfer unit not page but block or byte?
â Tim
Oct 4 at 1:12