TR is likewise 80 bits: 16 bits for the selector which behaves identically to a segment selector , and then another 64 for the base address of the TSS The one? From the SDM 15 :.
A subset of MSRs and associated bit fields, which do not change on future processor generations, are now considered architectural MSRs. On top of the empty ranges, there are also ranges that are explicitly marked as reserved, either generally or explicitly for later expansion of a particular MSR family.
Extract just table from Volume 4 of the SDM link :. Use pdftotext to convert it to plain text and manually trim the next table from the last page:. That pipeline left a bit of cruft towards the end thanks to quoted variants, so I count the actual number at architectural MSRs. The footnotes at the bottom of this post cover most of my notes, but I also wanted to dump some other resources that I found useful while discovering registers:.
The OSDev Wiki has collection of helpful pages on various x registers, including a great page on the behavior of the segment base MSRs. More registers means more expensive hardware. Zorf Zorf 5, 1 1 gold badge 25 25 silver badges 24 24 bronze badges.
I think it would be more accurate to say "x86 was popular enough that changing to anything else proved unprofitable". Remember, Intel tried to launch Itanium, which had int registers and was true bit, but failed due to lack of backwards compat.
In addition: There are other methods to increase CPU performance that is more cost efficient Even if more where introduced, you still need to update the instruction set and have compilers modified to use. Holds the program counter, the current instruction address. Modern CPUs have huge L1 size amounts of core-clocked memory, which while expensive, doesn't explain the perceptual register shortage. The register memory is utilised differently from L1 cache.
Unless of course registers have started have cache misses since I last checked in More architectural registers wouldn't be a problem for current x86 hardware other than insn encoding difficulties. Current designs already have over physical registers that architectural registers are renamed onto. The "really expensive" thing is the historical reason why the arch has so few architectural registers.
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SomeoneFromCA 11 months ago root parent prev next [—]. VLM 11 months ago parent prev next [—]. Essentially every device that does not use a x86 cpu did that. There's no point in waiting an entire development cycle to get a new smaller xalike when you could solder an ARM chip or similar to the board today. The vast majority of CPUs shipped are not x86 compatible.
Statista claims I know microchip the PIC people made press releases roughly annually as they shipped another billion flash microcontrollers. Google found the one from when they shipped their tenth billion PIC chip. I find it difficult to get x86 sales figures. Intel gross revenue is high because they have their fingers in everything. SomeoneFromCA 11 months ago parent prev next [—].
If you remove the obsolete stuff from x86, there will be no point to keep this old ISA altogether. One of the selling point of x86 is legacy support. You mean remove backwards compatibility and ruin the whole reason people use x86?
There exists both 16 bit protected mode available since the and 32 bit protected mode available since the There is also "32 bit realmode", which is not mentioned in the official documentation but simply a combination of existing states. Ditto for real mode paging and the like which finds more applications as emulator acid-tests than anything else. I thought the had bit protected mode, but it was badly implemented the only way to get back to real mode was a reboot , so they fixed it with the No, most people forget about it I had to be reminded by the above comment , but the did have a bit protected mode.
I am still upset after all this time, at what AMD recklessly did out of what might be the same misguided notion as the GP comment, they made instructions like LAHF invalid and removed much of segmentation, only to be forced to put much of it back later because people were actually using them. I suspect Intel was actually working on a more consistent extension to 64 bits too, but AMD beat them to it.
Yeah, but what about servers and data enters? For that reason, ARM servers exist. What obsolete stuff could you remove? If you want to actually meaningfully cut out a large amount of space on the processor, you'll have to cut into the actual instruction space and remove instructions that take up space in your execution units. Removing the bit and bit modes don't actually remove any instructions from the platform save the binary-coded decimal instructions --you're largely saving only a few bits of decoder table entries at best.
Furthermore, processors reset into bit mode on startup for compatibility reasons, so killing bit and bit mode would introduce major compatibility headaches. ISA extensions can be more easily removed since there's already a CPUID bit that tells operating systems and applications whether or not they are used.
The MPX extension for bounds checking is now regarded as a mistake, and Intel has already confirmed that they are removing it from future processor generations. The TSX extension for transactional memory is apparently on the hit list because of Spectre, and was removed from some processor generations.
The only significant processor execution unit space that is truly obsolete I can think is the x87 floating-point execution unit logic, with the concomitant MMX execution unit logic--SSE is just strictly better for everything here, except if you're trying to actually get the bit precision. But the existence of bit floating point in the bit ABI i. Didn't the switch to UEFI effectively reduce the scope of this problem to only apply to motherboard firmware? Operating systems no longer need bit code to boot.
There are a lot of x86 software out there. Even games switched to x64 binary relatively recently. I think if something is trully obsolete is already removed from hardware and emulated by the CPU with microcode. Yes, it's called Apple A1. Once you remove a single opcode, it's not really x86 any more, and you need emulation at OS level. But then, once you've done that, why not remove more instructions?
Why not remove all of them and start again on a much more power-efficient platform? Why not remove the memory model? One of the brilliant ideas in the A1 is a flag for whether the current process insists on the slower but more comprehensible x86 memory ordering.
You mean M1? That's pretty misleading. You can remove many instructions while keeping CPU x86 compatible. You can e. Very few apps require MMX as in can't work without it. Another option is to remove the instructions from hardware and emulate them in microcode.
A lot of software will ignore cpuid and assume features like MMX. This is a bug. That said, the MMX instructions in particular are so problematic to use and SSE ubiquitous and strictly better that I suspect you could introduce a processor that lacks MMX support and break almost nobody, certainly far fewer people than removing x I don't know if there is an implicit or explicit actual dependency on MMX anywhere. Perhaps, but compilers mostly assume its existence with the default flags.
We can't really demand compilers to create code that's compatible with all the ancient variations of a currently popular architecture. It's still good manners to include a function that exits with a clear error message about a required architecture feature that's missing. It wasn't fun. It doesn't matter. The only meaningful change would be to go with fixed length instructions and maybe get rid of the memory ordering guarantees.
If you do that you might as well switch to any other ISA that has these properties. Why are people downvoting this? Which is faster cache or register and why? In a computer, a register is the fastest memory. Registers are temporary memory units that store data and are located in the processor, instead of in RAM, so data can be accessed and stored faster. Cache memory is extremely fast memory that is built into a computer's central processing unit CPU.
How many types of registers are there? There are various types of Registers those are used for various purpose. What is the size of a register? The register can contain the address of a memory location where data is stored rather than the actual data itself. The number of registers that a CPU has and the size of each number of bits help determine the power and speed of a CPU.
For example a bit CPU is one in which each register is 32 bits wide. Is x86 better than x64? The same goes for using a x64 on a 32bit. It will function fine but it is not being used up too it's full potential. Is x86 dead? It's easy to see how in this industry, yes, x86 would be dead — if it were ever really alive!
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