Slideshow:
Memory alignment imposed by
the computer (memory)
architecture
Consequence of the
memory alignment requirement
Consequence of the
memory alignment requirement
Example record padding
Example record padding
Unpadded record:
Example record padding
Padded record:
- Alignment requirement (from
computer architecture):
- An integer variable
(= data item)
must be stored at an
address that is
divisible by 4
Example:
- A float variable (= data item)
must be stored at an
address that is
divisible by 4
- An double variable (= data item) must be stored at an address that is divisible by 8
- An integer variable
(= data item)
must be stored at an
address that is
divisible by 4
- Consquence:
- A record will contain "padding" (= empty) bytes to satify the alignment requirement
Graphically illustrated:
- Suppose a
record contains
these field:
Name: 30 characters - must start at an address that is divisible by 4 Addr: 256 characters - must start at an address that is divisible by 4 Gender: 1 character - must start at an address that is divisible by 4 BirthDay 10 characters - must start at an address that is divisible by 4 - Example: satisfying the
alignment requirement is
every field must be
located on an address that is
divisible by 4
