[10.10 64bit]-Why 8GB RAM Shows 7.8GB ?

[MR ZenWiz]

On Thu, Dec 23, 2010 at 2:11 PM, Rashkae <ubuntu at tigershaunt.com> wrote:
> On 10-12-22 05:06 PM, Ric Moore wrote:
>> On Wed, 2010-12-22 at 22:50 +0100, Thierry de Coulon wrote:
>>
>>> On Wednesday 22 December 2010 09:45:03 pm Jesse Palser wrote:
>>>
>>>> [10.10 64bit]-Why 8GB RAM Shows 7.8GB ?
>>>>
>>>> Hi,
>>>>
>>>> Recently made the switch to the 64bit version of Ubuntu 10.10.
>>>> I have 8GB DDR2 RAM installed on my computer
>>>> but System Monitor shows only 7.8GB ?
>>>> Where did 200MB RAM go?
>>>> Thanks!
>>>>
>>>> Ubuntu is best OS...
>>>>
>>>> Jesse
>>>>
>>>
>>> Most probably the usual "kilobit/kilobyte" stuff: one kilobit is 1000 bit, 1
>>> kilobyte is 1024; 1000/1024 is 0.9765 and 0.9765*8 is 7.8 so....
>>>
>> I think that explanation is spot on. Ric
>>
>
> No, that's always the wrong explanation with regards to Ram..... Hard
> Drives are where this comes from, since Hard drives (and for that
> matter, most other storage media) are marketed in base 10 Metric.  Ram,
> however, has always been marketed in Binary, (ie, MB and GB in Ram have
> always been in MiB and GiB.)
>
I suspect it has something to do with how user-level programs see
memory.  On my 4GB machine, SM shows 3.9GB but top shows 4051876k,
which is 4149121024, not quite a full 4GB == 4294967296 bytes.  The
difference is 145846272, roughly 142k, possibly the size of the kernel
or its reserved (not user accessible) memory.

Rakshae is absolutely right.