newbie qn.

[fookchen]

hi ppl,

i'm learning x86 assembly language now, however i'm encountering some difficulties in understanding how the 8086 works... in the specs for the 8086, a physical memory of 1MB is mentioned, and for the 80486, 4GB is mentioned.. Does it really means that there is 4GB of memory in the 80486 chip itself? And the other qn is, for Pentium 4, there is no physical memory mentioned, maybe someone can enlighten me here, thx in adv!

Ed

[CPUShack]

That number is simply the amount of physical memory the CPU can adress (or talk to)
a 486 has 32 address lines, so 2^32 is 4GB of memory (there are diffewrent ways memory can be acessed but this is the most simple)

The 8086 has 20 address lines so about 1 Meg of memory is adressable.

The P4 supports more memory through different acess modes (including paging, word adressing, etc)

[gshv]

Those numbers (1 MB, 4 GB) is the maximum amount of memory the processor can address directly. This memory is external to the processor, it does not reside on the processor itself. The processors do have small amount of memory on a chip, but this memory is always used for internal purposes - like registers, cache, different kinds of buffers, etc.

As for the Pentium 4 maximum memory size - it's not on cpu-world.com because it was not in the datasheet, and I was too lazy to look somewhere else. If I'm not mistaken the maximum memory size is the same as for the 80486 - 4 GB as the address bus is the same - 32 bits. Those new 64-bit processors should be able to access more memory.

Gennadiy

[CPUShack]

yah a TON more 1500 Petabytes or so

[Guest]

Ahh, that really clears up my confusion! thanks everyone!