69
votes
Can a CPU function with nothing more than a power supply and a ROM, using only the internal cache as RAM?
See this extremely detailed account of the PC boot sequence: http://www.drdobbs.com/parallel/booting-an-intel-architecture-system-par/232300699?pgno=2
Since no DRAM is available at this point, code ...
- 46.7k
60
votes
How is 255 Tbit/s processed in optical fiber communication?
It seems like you're referring specifically to http://www.nature.com/nphoton/journal/v8/n11/full/nphoton.2014.243.html . It can be read here: https://www.researchgate.net/publication/269099858_Ultra-...
- 40.8k
48
votes
Accepted
Can we not simply connect a battery to a RAM to prevent data loss during power cuts?
Short answer: You might be able to "connect a battery to a RAM to prevent data loss during power outage", but this depends on the type of RAM.
SRAM (Static Random Access Memory) is not DRAM, ...
- 16.1k
44
votes
Accepted
How is 255 Tbit/s processed in optical fiber communication?
Rather than worrying about a research paper that's pushing things to the limit first start by understanding the stuff sitting in front of you.
How does an SATA 3 hard drive in a home computer put 6 ...
- 6,902
36
votes
Accepted
Why use DDR instead of increasing clock speed?
With SDR, there are two clock edges per bit, but only at most one edge on the data line.
With high frequency communication, the analog bandwidth limits how close you can put edges together on any ...
- 171k
34
votes
Accepted
Why does RAM (any type) access time decrease so slowly?
It's because it's easier and cheaper to increase the bandwidth of the DRAM than to decrease the latency. To get the data from an open row of ram, a non trivial amount of work is necessary.
The ...
- 2,881
33
votes
Why execute code from RAM?
In addition to the speed & other features which others have already mentioned, executing code from RAM can be useful in bootloaders where you need to reprogram your micro's flash - you can't ...
- 14.5k
31
votes
Accepted
72-pin SIMM RAM: how do ground (Vss) and supply (Vcc) voltage pins work
The board is a multi-layer stackup, probably 4-layer.
This means that there are more layers inside the PCB on which other connections are routed.
You can tell this from the seemingly disappearing ...
- 64.8k
25
votes
Can we not simply connect a battery to a RAM to prevent data loss during power cuts?
Can we not simply connect a battery to a RAM to prevent data loss during power cuts? So can you tell me why is this not done?
Of course we do! It's called battery-backed SRAM, and it's widely used in ...
- 6,409
25
votes
Accepted
Enable vendor-disabled hardware on tablet?
Each of those modules is 4Gb (Gigabit). So you have 8Gb of RAM.
A byte is typically 8-bits, so that equates to 1GB of RAM, which is what your OS is reporting. There is no disabled memory that you can ...
- 64.8k
23
votes
Accepted
How can I access more than 15 addresses of data from my 8 bit incomplete computer?
the half of the byte in memory is the opcode and other half is the address
Well, that's one way of doing it, but there are lots of ways of doing it.
Instructions don't have to contain the address. ...
- 46.7k
20
votes
Is there a lower limit on operating frequency of CMOS SRAM?
No, there is no minimum frequency because it's static RAM. Any digital circuit that's described as "static" doesn't have a minimum frequency - it can operate with all signals held static for an ...
- 15.6k
19
votes
Accepted
Does a CPU completely freeze when using a DMA?
You are correct that the CPU cannot be accessing the memory during a DMA transfer. However there are two factors which in combination allow apparent parallel memory access by the CPU and the device ...
- 374
19
votes
72-pin SIMM RAM: how do ground (Vss) and supply (Vcc) voltage pins work
The PCB most probalby has 4 layers. The outer 2 which you can see are used to carry the signals and the inner 2 are power layers - 1 for ground and 1 for Vcc. This is the most common approach when ...
- 1,756
19
votes
Why execute code from RAM?
When you want to execute in RAM because it is faster, it's usually because that RAM is on-chip SRAM. This is a scarce resource, which you will probably want for data that requires read/write access.
...
- 13.9k
19
votes
Why execute code from RAM?
I didn't look at the datasheet for that micro. However, it is often the case in this situation that fetching from RAM is faster than fetching from the flash the program memory is implemented from.
...
- 312k
19
votes
Why use DDR instead of increasing clock speed?
The real problem is bandwidth. The highest frequency that a data line can generate (well, not counting slew rate) is when it's sending a 101010 data pattern, which occurs at half of the data rate. ...
- 40.8k
17
votes
Which is faster, Executing a program from ROM or RAM?
The datasheet should tell you how long each instruction takes, and what differences there are, if any, between executing from RAM or ROM.
For microcontroller that offer the option of executing from ...
- 312k
15
votes
How is 255 Tbit/s processed in optical fiber communication?
Ignoring the details of the specific transmission in question (which @alex.forencich has already discussed in considerable detail), it seems like it's probably useful to consider the more general case....
- 3,434
14
votes
Can a CPU function with nothing more than a power supply and a ROM, using only the internal cache as RAM?
Generally, the cache memory is not addressable. A program cannot store or retrieve data intentionally from it.
- 7,415
14
votes
Why execute code from RAM?
In addition to all good answers:
Why wouldn't I just always execute from RAM if the benefit is only
increased speed?
Because in an embedded system, usually you don't have the required amount of ...
- 23.7k
13
votes
Accepted
Microcontroller memory limitations
Several reasons. First, microcontrollers are generally not built with the same bleeding edge processes as the DRAM and Flash for your computer, so they do not take advantage of technological advance ...
- 40.8k
13
votes
Why execute code from RAM?
Other answers don't seem to have discussed power consumption much, which you specifically asked about.
The answer is that it depends somewhat on the microcontroller, but often execution from RAM can ...
- 1,871
12
votes
EEPROM with high endurance
Another solution could be to use a microcontroller with non-volatile FRAM. FRAM doesn't suffer from the same limitations on write cycles as EEPROM.
Some of the MSP430 products from TI are available ...
- 23.6k
12
votes
Accepted
Why is this clock signal connected to a capacitor to gnd?
C7 and R58 form a high pass filter, also known as a differentiator.
The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.
...
- 69.2k
12
votes
Why is this clock signal connected to a capacitor to gnd?
The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'...
- 171k
11
votes
Accepted
Is program code copied to SRAM from flash on microcontroller?
Most 8, 16 and 32 bit microcontrollers execute the program directly from flash. This is true of the STM32F103 range. Most microcontrollers are capable of executing the program from RAM, but only ...
- 5,295
Only top scored, non community-wiki answers of a minimum length are eligible