How Do I Calculate Memory Needed For A Display?

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I've just read this in The A+ Exams Guide by Christopher A. Crayton:

It says a 640x480 display at 8bits (256 colours) needs 512K of vidoe memory.

But 640 * 480 * 8 = 2,457,600

Do I then divide it by 8 (bits in a byte) and then divide that by 1024 (bytes in a KB)? = 300?

 

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Actually how am I supposed to work that out in an exam? I've only got 10 fingers.

I'll just learn the tables instead.

 

24 bit colour depth equals 3 bytes (24 divide by 3)
16 bit would equal 2 bytes and so on.

multiply the screen resolution you want to use by the bit depth..

for example...640 x 480 x 3
= 921600 (bytes)

then divide by 1048576
= 0.87890625 MB per screen

Suffice to say you would need 1MB of video memory in this case

You won't be expected to calculate this in the exam,especially since you won't be allowed a calculator,but you will be expected to know the answer!So yup...time to learn those tables....

 

You have it very close.

In this particular case 307K is the right answer.

640*480 is the key for this - That equates to 307k pixels.

8 bits is a byte - and for 256 colours that byte uses a 'lookup' into the colour table for display.

So a 512K card would do nicely.

Harry.

 

Cheers Guys