How are CPU features disabled?

[lexidobe]

So are features like hyperthreading, overclocking, etc. disabled physically, or in the CPU's firmware(if it has firmware)? Do CPUs have some sort of memory or chip on them to hold product information like the SKU and or factory settings? How does the motherboard know if, for example you have a Core i5 7600 vs. a 7600K? Are the 2 chips physically different? Does the CPU have some sort of read only memory or something to hold these factory settings? Sorry if I do not make sense, but I am very curious.

[scottyseng]

5 minutes ago, lexidobe said:

So are features like hyperthreading, overclocking, etc. disabled physically, or in the CPU's firmware(if it has firmware)? Do CPUs have some sort of memory or chip on them to hold product information like the SKU and or factory settings? How does the motherboard know if, for example you have a Core i5 7600 vs. a 7600K? Are the 2 chips physically different? Does the CPU have some sort of read only memory or something to hold these factory settings? Sorry if I do not make sense, but I am very curious.

Read the recent posts on this thread:

They do it via microcode / some features are physically disabled for the CPU if they don't meet standards.

[Kamina]

Via Microcode. 

[ARikozuM]

They can be disabled physically by cutting the interconnects, degraded in firmware (which is why one CPU was reversible to a higher end a few years back), or completely left out of firmware. They actually have a chip that holds all of the data, it's the reason why your BIOS can identify that you have an i5-4690K. There is no difference between the 6700K and 6700 aside from the stability of the K for overclocking and efficiency. CPUs utilize ROMs.

[lexidobe]

14 hours ago, Kamina said:

Via Microcode. 

Is microcode stored on the CPU?

[NumLock21]

Intel did that a while back, with the upgrade your cpu via scratch off card.

[ARikozuM]

Just now, lexidobe said:

Is microcode stored on the CPU?

Yes. It is located on the same ROM chip that holds the instruction sets and identifiers.

[Drak3]

Every desktop i5 and quad core i7 are physically idential. They just have different microcode based on how efficient and stable the individual products are.

Chips like Xeon and X99 i7 can, and often do, undergo a interconnect cutting to permanently disable cores, but the defunct cores physically remain.

[lexidobe]

14 hours ago, ARikozuM said:

They can be disabled physically by cutting the interconnects, degraded in firmware (which is why one CPU was reversible to a higher end a few years back), or completely left out of firmware. They actually have a chip that holds all of the data, it's the reason why your BIOS can identify that you have an i5-4690K. There is no difference between the 6700K and 6700 aside from the stability of the K for overclocking and efficiency. CPUs utilize ROMs.

So in theory could you flash a microcode for an overclockable CPU to a non overclockable and turn it into a K? If not, could you IN THEORY un solder the ROM chip and, if you could get your hands on one, solder a ROM chip from a K edition on and overclock it?

[lexidobe]

In theory, why could you not just flash a microcode for an unlocked CPU onto a locked one and overclock it?

[ARikozuM]

1 minute ago, lexidobe said:

In theory, why could you not just flash a microcode for an unlocked CPU onto a locked one and overclock it?

Read Only Memory. Unless you have a very capable friend, you're not likely to get it done. 

[lexidobe]

15 hours ago, ARikozuM said:

Yes. It is located on the same ROM chip that holds the instruction sets and identifiers.

Is it somewhere on the die?

[Drak3]

1 minute ago, lexidobe said:

In theory, why could you not just flash a microcode for an unlocked CPU onto a locked one and overclock it?

Because there is no publically available tool to flash a custom/different code.

[ARikozuM]

Just now, lexidobe said:

Is it somewhere on the die?

It's on the CPU itself. You have very little contact with the CPU on the software side.

[lexidobe]

14 hours ago, ARikozuM said:

Read Only Memory. Unless you have a very capable friend, you're not likely to get it done. 

Is it physically impossible to write to read only memory? It was obviously written to at one point.

[lexidobe]

14 hours ago, Drak3 said:

Because there is no publically available tool to flash a custom/different code.

Would it be possible to make one, or completely impossible?

[ARikozuM]

Just now, lexidobe said:

Is it physically impossible to write to read only memory? It was obviously written to at one point.

You know that write-protect tab on floppies or SD cards? Think of that, except there's no switch.

[lexidobe]

14 hours ago, ARikozuM said:

You know that write-protect tab on floppies or SD cards? Think of that, except there's no switch.

Oh, so writing to it was disabled after the code was flashed? How do microcode updates work then? 

[ARikozuM]

Just now, lexidobe said:

Oh, so writing to it was disabled after the code was flashed? How do microcode updates work then? 

BIOS and chipset. Your CPU isn't the only object with microcode. 

[Drak3]

1 minute ago, lexidobe said:

Would it be possible to make one, or completely impossible?

It's possible, but barely. Without Intel or AMD resources and insider knowledge, it would take years of development.

 

2 minutes ago, ARikozuM said:

You know that write-protect tab on floppies or SD cards? Think of that, except there's no switch.

ROM isn't really Read Only. The ROM on CPUs are extremely hard to write to, but it isn't impossible.

[lexidobe]

14 hours ago, ARikozuM said:

You know that write-protect tab on floppies or SD cards? Think of that, except there's no switch.

But could you not IN THEORY un solder the ROM chip and IF you could find a chip, which odds are almost none, could you not solder on a chip for an unlocked CPU and turn it into a K?

[ARikozuM]

Just now, Drak3 said:

ROM isn't really Read Only. The ROM on CPUs are extremely hard to write to, but it isn't impossible.

Obviously not since BIOS ROMs are written to all the time, but I'm making an example (as oversimplified as it is, mind you).

[ARikozuM]

Just now, lexidobe said:

But could you not IN THEORY un solder the ROM chip and IF you could find a chip, which odds are almost none, could you not solder on a chip for an unlocked CPU and turn it into a K?

Have you seen a photo of a delidded CPU? That's what you'd be up against.

Spoiler

 

[lexidobe]

14 hours ago, ARikozuM said:

Obviously not since BIOS ROMs are written to all the time, but I'm making an example (as oversimplified as it is, mind you).

I like your example, I get that. So to write to it, you would have to make a custom tool?

[lexidobe]

14 hours ago, ARikozuM said:

Have you seen a photo of a delidded CPU? That's what you'd be up against.

  Reveal hidden contents

 

Oh, I thought it was one of the little chips on the bottom.