98
votes
Accepted
Why not make one big CPU core?
The problem lies with the assumption that CPU manufacturers can just add more transistors to make a single CPU core more powerful without consequence.
To make a CPU do more, you have to plan what ...
- 56.5k
86
votes
Accepted
What limits CPU speed?
Practically, what limits CPU speed is both the heat generated and the gate delays, but usually, the heat becomes a far greater issue before the latter kicks in.
Recent processors are manufactured ...
- 1,862
85
votes
Accepted
Why is RAM not put on the CPU chip?
Intel's Haswell (or at least those products that incorporate the Iris Pro 5200 GPU) and IBM's POWER7 and POWER8 all include embedded DRAM, "eDRAM".
One important issue that has led eDRAM not to be ...
- 1,614
76
votes
Accepted
Why don't we make CPUs with 1000s of layers to make use of space in the third dimension?
The two killer reasons are yield, and heat.
Yield. Every time you do a process step, you get less than 100% perfection. Let's say you get 99% perfection per step. In a process with 20 steps, you would ...
- 140k
73
votes
Accepted
Why do CPUs need so much current?
CPUs are not 'simple' by any stretch of the imagination. Because they have a few billion transistors, each one of which will have some small leakage at idle and has to charge and discharge gate and ...
- 39.6k
66
votes
Accepted
Why is there no `nand` instruction in modern CPUs?
http://www.ibm.com/support/knowledgecenter/ssw_aix_61/com.ibm.aix.alangref/idalangref_nand_nd_instrs.htm : POWER has NAND.
But generally modern CPUs are built to match automated code generation by ...
- 44.9k
55
votes
How can an FPGA outperform a CPU?
CPU's are sequential processing devices. They break an algorithm up into a sequence of operations and execute them one at a time.
FPGA's are (or, can be configured as) parallel processing devices. ...
- 4,906
51
votes
Accepted
How can a CPU deliver more than one instruction per cycle?
First, as Keelan's comment and Turbo J's answer point out, the measurement was 113,093 Dhrystone MIPS not native MIPS.
The Ivy Bridge microarchitecture of the i7 3630QM can only commit 4 fused µops ...
- 1,637
51
votes
Accepted
Is transistor the only electronic component on a CPU?
The logical blocks and memories can be made out of only transistors. The important question is: are all of the circuits on CPUs logical blocks and memories, or is there anything else?
The answer ...
- 5,836
49
votes
Accepted
When Intel / AMD choose their Nanometer Processes, why were the specific numbers, 5, 7, 10, 14, 22, 32, 45, etc chosen?
There are a number of different reasons for this.
The numbers aren't chosen
Modern CPU manufacturing processes, at least for top-of-the line mainstream CPUs such as Intel Xeon and Core, AMD Epyc and ...
- 740
43
votes
Why do CPU's typically connect to only one bus?
The approach which you show is quite an old topology for motherboards - it predates PCIe which really puts it back somewhere in the '00s. The reason is primarily due to difficulties of integration.
...
- 56.5k
43
votes
Accepted
Why don't we see faster 7400 series chips?
As technology size decreases, wire resistance/capacitance cannot scale proportionally to the propagation delay of the now faster/smaller transistors. Because of that, the delay becomes largely wire ...
- 4,225
41
votes
Accepted
What is the lowest level of CPU programming above transistors?
In my CS program, my professor has claimed that NAND gates are the
most basic gate to engineer, and so every other gate and higher-level
circuits found in CPUs are made from NAND gates
“Yeah? Well, ...
- 40.2k
40
votes
What limits CPU speed?
The heat issue is well covered by fuzzyhair. To summarize the transmission delays, consider this: The time needed for an electrical signal to cross the motherboard is now more than one clock cycle of ...
- 2,073
40
votes
Why not make one big CPU core?
In addition to the other answers, there is another element: chip yields. A modern processor has several billion transistors in them, each and every one of those transistors have to work perfectly in ...
- 1,424
40
votes
Why does Intel's Haswell chip allow floating point multiplication to be twice as fast as addition?
This possibly answers the title of the question, if not the body:
Floating point addition requires aligning the two mantissa's before adding them (depending on the difference between the two ...
- 4,451
40
votes
For mainstream computing what are the practical advantages of 64-bit register size CPUs given the needs of today and the near future?
With 48bits you can address 256TiB of RAM, plenty of space to be useful
Its not about address space (*).
In fact most 64-bit desktop processors have a 48-bit address bus. There is little point ...
- 56.5k
37
votes
How can an FPGA outperform a CPU?
Markt has this mostly right, but I'm going to throw in my 2 cents here:
Imagine that I told you that I wanted to write a program which reversed the order of bits inside of a 32-bit integer. ...
- 3,239
37
votes
Accepted
How can cache be that fast?
This CPU has...
2 cores
A 32-KB instruction and 32-KB data first-level cache (L1) for each core
Since there are two cores, we can expect the benchmark to run two threads in parallel. Their ...
- 57.4k
37
votes
Why aren't CPUs cooled from below as well as above?
They aren't cooled from below because they have pins on the bottom, and FR4 below that.
Due to having a much lower thermal conductivity,
$$
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\text{Copper:} & 385\phantom{.25} &...
- 63.3k
37
votes
Accepted
How does the current processor technology with low clock rates (<10 GHz) deals with mmWave (>10 GHz) technology used in 5G?
So, how do processors deal with the frequencies in the range of 20-100 GHz?
They don't.
Even if we consider a demodulation of data to lower frequencies from carrier frequencies, there needs to be a ...
- 6,361
33
votes
Accepted
What stops an assembly program from crashing the operating system?
In the end, all programs are machine code, regardless of whether the source language was assembler or a high-level language.
The important thing is that there are hardware mechanisms that limit what ...
- 164k
32
votes
Accepted
How can an FPGA outperform a CPU?
All of the other popular answers presented here talk about literal differences between FPGAs and CPUs. They point out the parallel nature of the FPGA vs the sequential nature of a CPU, or give ...
- 1,543
32
votes
Why is there no `nand` instruction in modern CPUs?
The cost of such an ALU functions is
1) the logic that performs the function itself
2) the selector that selects this function result instead of the others out of all ALU functions
3) the cost of ...
- 47.7k
32
votes
Using CPU heat to generate electricity
The issue with thermoelectric generators is they are horrendously inefficient.
For a CPU you HAVE to get rid of the heat they produce or they melt down.
You could hook up a peltier module and ...
- 45.6k
31
votes
How can cache be that fast?
@peufeu's answer points out that these are system-wide aggregate bandwidths. L1 and L2 are private per-core caches in Intel Sandybridge-family, so the numbers are 2x what a single core can do. But ...
- 1,232
30
votes
Why is there no `nand` instruction in modern CPUs?
Turn it around - first see why Nand was popular in hardware logic design - it has several useful properties there. Then ask whether those properties still apply in a CPU instruction...
TL/DR - they ...
- 65.7k
30
votes
Accepted
FPGA CPUs, how to find the max speed?
The speed of a design is limited by several things. The biggest will most likely be the propagation delay through the combinatorial logic in your design, called the critical path. If you use a fast ...
- 39.6k
30
votes
Accepted
Can you make a CPU out of electronic components drawn by hand on paper?
If the gain of a single inverter is less than unity, then it will not be possible to combine any significant number of gates together to build a larger circuit. The signal levels will just peter out.
...
- 164k
Only top scored, non community-wiki answers of a minimum length are eligible