Confused on how they figured out bytes, book example:

AI Thread Summary
The discussion centers on the confusion regarding the calculation of cache sizes and bit fields in a computer architecture example. The Intrinsity caches are identified as 16 KB, with 256 blocks and 16 words per block, leading to the conclusion that 64 bytes equals 512 bits. Participants clarify that the 32-bit address is broken down into components, where 8 bits are for the byte and 6 bits are for the index, resulting in the tag field being 18 bits. The total bits calculation reflects the number of blocks multiplied by the sum of data, tag, and valid bits. Ultimately, the confusion stems from a typo in the book regarding the cache size, which is confirmed to be 16 * 1024 bytes rather than 16E3.
mr_coffee
Messages
1,613
Reaction score
1
The Intrinsity caches are 16 KB caches and have 256 blocks with 16 words per block.

Thus data is 64 bytes = 512 bytes.
The tag field is 18 bits (32 - (8 + 6)).
Total bits = 256 x (Data + Tag + Valid)
= 256 x (512 bits + 18 bits + 1 bit)
= 135,936 bitsI'm confused on how they got 64 bytes then said = 512 bytes.

Also where did they get (32 - (8+6))?
I think i know where they got 32, because its a 32 bit address.Thank you.

I took 16E3/265 = 62.5 not 64.

EDIT:

Okay I got alittle farther...

16E3/16 = 1000 which is ~ 2^10 words, and with a block size of 4 words (2^2), but still not sure how they got 64 and 512, nor the (8+6).
 
Last edited:
Physics news on Phys.org
64 bytes = 512 bits

Isn't that just what they meant?
 
16KB is not 16E3 but 16*1024.
16*1024/16 is not ~ but = 2^10.
 
Ahhh thanks guys!

that makes sense... it was a typo in the book.
okay so I understand the 512 bits.

for the:
The tag field is 18 bits (32 - (8 + 6)).
Total bits = 256 x (Data + Tag + Valid)

32 bits address, is the 8 because 8 bits in a byte? still not seeing the 6 though.

Also is the 256 x (data + tag + valid) because they said there is 256 blocks?
 

Similar threads

Replies
7
Views
1K
Replies
8
Views
2K
Replies
7
Views
3K
Replies
6
Views
3K
Replies
10
Views
2K
Replies
1
Views
7K
Back
Top