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Recently, I found out a YT channel of a man who build a 8-bit computer and explain how.

In his video on the registers, he uses a D flip-flop, and in his other video on the ram, I understood that he says he'll use the same system as the registers, and that's called 'Static RAM', and the 'Dynamic RAM' is faster.

But I think that the registers are faster than RAM, so if dynamic ram is faster than static ram, which uses the same kind of system than the registers to store, they are slower than dynamic ram...

Did I not understand the videos or something else?

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  • \$\begingroup\$ In general, static RAM is faster than dynamic RAM, but that doesn't mean that every static RAM is faster than every dymanic RAM. Registers are also RAM, nearly always static, and generally of a faster variant than static RAM used for cache or main memory. \$\endgroup\$ – Wouter van Ooijen Feb 17 '17 at 11:50
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    \$\begingroup\$ Anyone building a computer from basic parts must be motivated by something that helps them learn stuff; stuff that most EEs have learnt years ago. Because of this, and the somewhat dubious reason to post a YT video, I conclude that what they offer as advice or facts, has to be tarnished. \$\endgroup\$ – Andy aka Feb 17 '17 at 12:06
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    \$\begingroup\$ @Andyaka I think that's a bit harsh - while quite a lot of youtube stuff is junk, some of it is genuinely educational gems. The building from scratch is a hobby project like building a giant model railway; the journey is the destination. Also it's something you can show off to the audience. \$\endgroup\$ – pjc50 Feb 17 '17 at 12:07
  • \$\begingroup\$ It's not harsh or even a bit harsh but that is my opinion. The giant model railway, however, is much more interesting because of miniaturisation; I've never seen any hobbyist try to build a model railway that is a hundred times bigger than the real thing! \$\endgroup\$ – Andy aka Feb 17 '17 at 12:11
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There is DRAM which uses a capacitor to store a charge to represent the stored bit. A row of transistors is used to connect a row of capacitors to the read/write circuitry to put the data into a set of latches to read it and also feed it back into the row to refresh the capacitors' charge which was depleted into the latch's input.

The capacitors will self discharge over time so each row needs to be refreshed periodically. In most DRAM you can only read or write a single row at a time.

This type is used for the main RAM because it is cheaper in silicon per bit.


Then there is SRAM which uses flipflops to store the data which takes a half dozen transistors per bit. It has a constant output available so can be read at any time using a MUX, instead of having to wait until the proper row can be selected.

This type is used internally for nearly everything on the cpu (including caching the current row in DRAM) because it is much faster.

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I think that the registers are faster than RAM

depending on the context under which the term "register" is used. typically they are part of the RAM that the cpu has special access to. cpus typically (=not always) have faster access to those memory addresses.

other times, "register" is nothing but ram that is specifically wired to certain peripherals.

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  • \$\begingroup\$ "the RAM that the cpu has special access to" - What do you mean by that? Please clarify. \$\endgroup\$ – JimmyB Feb 17 '17 at 12:44
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the registers are faster than RAM

Today? Yes, very much so.

In the 80s era of 8-bit computers? No, it was often possible to access the RAM in one processor cycle because the processor was comparatively slow.

Off-chip RAM is nearly always DRAM. On-chip RAM is usually SRAM, the same technology as the registers. Confusingly, PIC architecture designers make no distinction between on-chip RAM and registers and just call everything a "register".

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  • \$\begingroup\$ Registers were much faster than RAM, but RAM was about as fast as an ALU that was optimized for space rather than speed. CPU performance was limited by the slowest part, which would often be the ALU. \$\endgroup\$ – supercat Aug 31 '17 at 20:49

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